feat(rust): port divsufsort

Move the dictionary builder's suffix-array construction from lib/dictBuilder/divsufsort.c to rust/src/divsufsort.rs, the first dictBuilder module to migrate. It rides on the dict-builder cargo feature dimension introduced by the previous commit. divsufsort() is a self-contained algorithm (two-stage sort of type-B* substrings via sssort, rank refinement via trsort, then induced sorting of the full array), so its context-free signature allows a direct symbol takeover: the Rust #[no_mangle] export provides the existing `divsufsort` symbol and the C file becomes a declaration-only shim that just keeps the header's prototypes in the build. Only divsufsort() moved; divbwt() has no callers anywhere in zstd, so it is now declaration-only, keeping the Rust export surface minimal. The unused openMP parameter is retained for signature compatibility (zstd never defines LIBBSC_OPENMP). The port is a mechanical translation of the exact configuration zstd compiles: ALPHABET_SIZE=256, SS_INSERTIONSORT_THRESHOLD=8, SS_BLOCKSIZE=1024, SS_MISORT_STACKSIZE=16, SS_SMERGE_STACKSIZE=32, TR_STACKSIZE=64. Every C `int*` cursor into the SA buffer becomes an `isize` index into a single `&mut [i32]` slice, preserving the pointer arithmetic (including transient one-before-the-range cursors and the bitwise-complement rank marking) while staying bounds-checked; all value arithmetic keeps C int semantics. The C -1/-2 error results are preserved, with Vec::try_reserve_exact standing in for the bucket-array malloc failure path. Behavior is bit-identical by construction and by measurement (see test plan); runtime on an 11 MB training buffer is within ~5% of the C build end-to-end. Users see no behavioral change: dictionaries trained through ZDICT_trainFromBuffer_legacy() are byte-identical to the C build. The only external difference is that the never-called `divbwt` symbol is no longer defined in the library. Test plan: - cd rust && cargo fmt --check && cargo clippy --all-targets -- -D warnings && cargo test --all-targets && cargo build --release (125 tests pass; new unit tests cover empty/one/two-byte inputs, all-equal bytes, an exact hand-computed "abracadabra" SA, and fixed-seed LCG buffers at 256-, 4-, and 2-symbol alphabets verified against a naive reference sort plus permutation/sorted invariants) - Feature matrix: cargo build --release --no-default-features --features compression,decompression (and decompression-only, compression-only, compression,dict-builder); `divsufsort` is exported only when dict-builder is enabled - make -C tests fuzzer && ./tests/fuzzer -i1 --no-big-tests (includes ZDICT training tests): pass - make -C tests test-rust-lib-smoke: pass - make -C tests test-invalidDictionaries: pass - make -C programs zstd zstd-dictBuilder zstd-small zstd-compress zstd-decompress: build; compress/decompress round-trip verified - Byte-identity vs pristine C build (commit 959e4852): a harness calling ZDICT_trainFromBuffer_legacy() (the only zstd path reaching divsufsort) and divsufsort() directly, linked against both libzstd.a builds, produces byte-identical dictionaries (80,288 B and full 112,640 B capacity) and byte-identical suffix arrays on a 1 MB source set and an 11 MB binary/repetitive set; a differential driver over 148 random and structured buffers (sizes 3..6000, alphabets 1..256, Fibonacci word, sawtooth, 6 KB near-constant) shows zero mismatches. The CLI --train path could not be exercised because the Rust CLI frontend rejects --train in both the pristine and ported builds (a pre-existing migration gap unrelated to this change).
build(rust): add dict-builder cargo feature dimension
2026-07-11 14:23:39 +02:00 · 2026-07-11 14:23:39 +02:00 · 2026-07-11 09:39:26 +02:00
11 changed files with 2858 additions and 1907 deletions
@@ -142,6 +142,7 @@ endif()
 set(_zstd_rust_features)
 set(_zstd_rust_compression 0)
 set(_zstd_rust_decompression 0)
+set(_zstd_rust_dictbuilder 0)
 if(ZSTD_BUILD_COMPRESSION)
    list(APPEND _zstd_rust_features compression)
    set(_zstd_rust_compression 1)
@@ -150,6 +151,10 @@ if(ZSTD_BUILD_DECOMPRESSION)
    list(APPEND _zstd_rust_features decompression)
    set(_zstd_rust_decompression 1)
 endif()
+if(ZSTD_BUILD_DICTBUILDER)
+    list(APPEND _zstd_rust_features dict-builder)
+    set(_zstd_rust_dictbuilder 1)
+endif()

 set(_zstd_rust_huf_mode default)
 if(_zstd_huf_force_x1)
@@ -190,7 +195,7 @@ if(_zstd_rust_features)
 endif()

 set(_zstd_rust_build_config
-    "c${_zstd_rust_compression}-d${_zstd_rust_decompression}-${_zstd_rust_huf_mode}")
+    "c${_zstd_rust_compression}-d${_zstd_rust_decompression}-b${_zstd_rust_dictbuilder}-${_zstd_rust_huf_mode}")
 set(ZSTD_RUST_MANIFEST "${ZSTD_SOURCE_DIR}/rust/Cargo.toml")
 set(ZSTD_RUST_TARGET_DIR
    "${CMAKE_CURRENT_BINARY_DIR}/rust-target/${_zstd_rust_build_config}")
@@ -73,7 +73,9 @@ if rust_huf_force_x1 and rust_huf_force_x2
  error('HUF_FORCE_DECOMPRESS_X1 and HUF_FORCE_DECOMPRESS_X2 are mutually exclusive')
 endif

-rust_features = ['compression', 'decompression']
+# Meson always compiles the dictBuilder sources above, so the Rust archive
+# must always carry the matching dict-builder module set.
+rust_features = ['compression', 'decompression', 'dict-builder']
 rust_huf_mode = 'default'
 rust_huf_c_args = []
 if rust_huf_force_x1
@@ -96,7 +98,7 @@ if rust_target == ''
  endif
 endif

-rust_build_config = 'c1-d1-' + rust_huf_mode
+rust_build_config = 'c1-d1-b1-' + rust_huf_mode
 rust_target_dir = join_paths(meson.current_build_dir(), 'rust-target', rust_build_config)
 is_msvc = cc_id == compiler_msvc or cc_id == 'clang-cl'
 rust_staticlib_name = is_msvc ? 'zstd_rs.lib' : 'libzstd_rs.a'
@@ -84,16 +84,20 @@ endif
 ifneq ($(ZSTD_LIB_DECOMPRESSION),0)
 RUST_CARGO_FEATURES += decompression
 endif
+ifneq ($(ZSTD_LIB_DICTBUILDER),0)
+RUST_CARGO_FEATURES += dict-builder
+endif

+RUST_MODULE_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-b$(ZSTD_LIB_DICTBUILDER)
 RUST_HUF_FEATURE :=
-RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-default
+RUST_BUILD_CONFIG := $(RUST_MODULE_CONFIG)-default
 ifneq ($(RUST_HUF_FORCE_X1),0)
 RUST_HUF_FEATURE := huf-force-decompress-x1
-RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-huf-force-decompress-x1
+RUST_BUILD_CONFIG := $(RUST_MODULE_CONFIG)-huf-force-decompress-x1
 endif
 ifneq ($(RUST_HUF_FORCE_X2),0)
 RUST_HUF_FEATURE := huf-force-decompress-x2
-RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-huf-force-decompress-x2
+RUST_BUILD_CONFIG := $(RUST_MODULE_CONFIG)-huf-force-decompress-x2
 endif
 ifneq ($(RUST_HUF_FEATURE),)
 ifneq ($(ZSTD_LIB_DECOMPRESSION),0)
@@ -24,1890 +24,9 @@
 * OTHER DEALINGS IN THE SOFTWARE.
 */

-/*- Compiler specifics -*/
-#ifdef __clang__
-#pragma clang diagnostic ignored "-Wshorten-64-to-32"
-#endif
-
-#if defined(_MSC_VER)
-#  pragma warning(disable : 4244)
-#  pragma warning(disable : 4127)    /* C4127 : Condition expression is constant */
-#endif
-
-
-/*- Dependencies -*/
-#include <assert.h>
-#include <stdio.h>
-#include <stdlib.h>
-
+/* divsufsort() is implemented in rust/src/divsufsort.rs, which provides the
+ * symbol directly.  This translation unit keeps the header's prototypes in
+ * the build so the dictionary builder continues to compile against the
+ * original interface.  divbwt() has no callers in zstd and is declaration-
+ * only; it moves to Rust if a user ever appears. */
 #include "divsufsort.h"
-
-/*- Constants -*/
-#if defined(INLINE)
-# undef INLINE
-#endif
-#if !defined(INLINE)
-# define INLINE __inline
-#endif
-#if defined(ALPHABET_SIZE) && (ALPHABET_SIZE < 1)
-# undef ALPHABET_SIZE
-#endif
-#if !defined(ALPHABET_SIZE)
-# define ALPHABET_SIZE (256)
-#endif
-#define BUCKET_A_SIZE (ALPHABET_SIZE)
-#define BUCKET_B_SIZE (ALPHABET_SIZE * ALPHABET_SIZE)
-#if defined(SS_INSERTIONSORT_THRESHOLD)
-# if SS_INSERTIONSORT_THRESHOLD < 1
-#  undef SS_INSERTIONSORT_THRESHOLD
-#  define SS_INSERTIONSORT_THRESHOLD (1)
-# endif
-#else
-# define SS_INSERTIONSORT_THRESHOLD (8)
-#endif
-#if defined(SS_BLOCKSIZE)
-# if SS_BLOCKSIZE < 0
-#  undef SS_BLOCKSIZE
-#  define SS_BLOCKSIZE (0)
-# elif 32768 <= SS_BLOCKSIZE
-#  undef SS_BLOCKSIZE
-#  define SS_BLOCKSIZE (32767)
-# endif
-#else
-# define SS_BLOCKSIZE (1024)
-#endif
-/* minstacksize = log(SS_BLOCKSIZE) / log(3) * 2 */
-#if SS_BLOCKSIZE == 0
-# define SS_MISORT_STACKSIZE (96)
-#elif SS_BLOCKSIZE <= 4096
-# define SS_MISORT_STACKSIZE (16)
-#else
-# define SS_MISORT_STACKSIZE (24)
-#endif
-#define SS_SMERGE_STACKSIZE (32)
-#define TR_INSERTIONSORT_THRESHOLD (8)
-#define TR_STACKSIZE (64)
-
-
-/*- Macros -*/
-#ifndef SWAP
-# define SWAP(_a, _b) do { t = (_a); (_a) = (_b); (_b) = t; } while(0)
-#endif /* SWAP */
-#ifndef MIN
-# define MIN(_a, _b) (((_a) < (_b)) ? (_a) : (_b))
-#endif /* MIN */
-#ifndef MAX
-# define MAX(_a, _b) (((_a) > (_b)) ? (_a) : (_b))
-#endif /* MAX */
-#define STACK_PUSH(_a, _b, _c, _d)\
-  do {\
-    assert(ssize < STACK_SIZE);\
-    stack[ssize].a = (_a), stack[ssize].b = (_b),\
-    stack[ssize].c = (_c), stack[ssize++].d = (_d);\
-  } while(0)
-#define STACK_PUSH5(_a, _b, _c, _d, _e)\
-  do {\
-    assert(ssize < STACK_SIZE);\
-    stack[ssize].a = (_a), stack[ssize].b = (_b),\
-    stack[ssize].c = (_c), stack[ssize].d = (_d), stack[ssize++].e = (_e);\
-  } while(0)
-#define STACK_POP(_a, _b, _c, _d)\
-  do {\
-    assert(0 <= ssize);\
-    if(ssize == 0) { return; }\
-    (_a) = stack[--ssize].a, (_b) = stack[ssize].b,\
-    (_c) = stack[ssize].c, (_d) = stack[ssize].d;\
-  } while(0)
-#define STACK_POP5(_a, _b, _c, _d, _e)\
-  do {\
-    assert(0 <= ssize);\
-    if(ssize == 0) { return; }\
-    (_a) = stack[--ssize].a, (_b) = stack[ssize].b,\
-    (_c) = stack[ssize].c, (_d) = stack[ssize].d, (_e) = stack[ssize].e;\
-  } while(0)
-#define BUCKET_A(_c0) bucket_A[(_c0)]
-#if ALPHABET_SIZE == 256
-#define BUCKET_B(_c0, _c1) (bucket_B[((_c1) << 8) | (_c0)])
-#define BUCKET_BSTAR(_c0, _c1) (bucket_B[((_c0) << 8) | (_c1)])
-#else
-#define BUCKET_B(_c0, _c1) (bucket_B[(_c1) * ALPHABET_SIZE + (_c0)])
-#define BUCKET_BSTAR(_c0, _c1) (bucket_B[(_c0) * ALPHABET_SIZE + (_c1)])
-#endif
-
-
-/*- Private Functions -*/
-
-static const int lg_table[256]= {
- -1,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
-  5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
-  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
-  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
-  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
-  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
-  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
-  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
-};
-
-#if (SS_BLOCKSIZE == 0) || (SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE)
-
-static INLINE
-int
-ss_ilg(int n) {
-#if SS_BLOCKSIZE == 0
-  return (n & 0xffff0000) ?
-          ((n & 0xff000000) ?
-            24 + lg_table[(n >> 24) & 0xff] :
-            16 + lg_table[(n >> 16) & 0xff]) :
-          ((n & 0x0000ff00) ?
-             8 + lg_table[(n >>  8) & 0xff] :
-             0 + lg_table[(n >>  0) & 0xff]);
-#elif SS_BLOCKSIZE < 256
-  return lg_table[n];
-#else
-  return (n & 0xff00) ?
-          8 + lg_table[(n >> 8) & 0xff] :
-          0 + lg_table[(n >> 0) & 0xff];
-#endif
-}
-
-#endif /* (SS_BLOCKSIZE == 0) || (SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE) */
-
-#if SS_BLOCKSIZE != 0
-
-static const int sqq_table[256] = {
-  0,  16,  22,  27,  32,  35,  39,  42,  45,  48,  50,  53,  55,  57,  59,  61,
- 64,  65,  67,  69,  71,  73,  75,  76,  78,  80,  81,  83,  84,  86,  87,  89,
- 90,  91,  93,  94,  96,  97,  98,  99, 101, 102, 103, 104, 106, 107, 108, 109,
-110, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126,
-128, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142,
-143, 144, 144, 145, 146, 147, 148, 149, 150, 150, 151, 152, 153, 154, 155, 155,
-156, 157, 158, 159, 160, 160, 161, 162, 163, 163, 164, 165, 166, 167, 167, 168,
-169, 170, 170, 171, 172, 173, 173, 174, 175, 176, 176, 177, 178, 178, 179, 180,
-181, 181, 182, 183, 183, 184, 185, 185, 186, 187, 187, 188, 189, 189, 190, 191,
-192, 192, 193, 193, 194, 195, 195, 196, 197, 197, 198, 199, 199, 200, 201, 201,
-202, 203, 203, 204, 204, 205, 206, 206, 207, 208, 208, 209, 209, 210, 211, 211,
-212, 212, 213, 214, 214, 215, 215, 216, 217, 217, 218, 218, 219, 219, 220, 221,
-221, 222, 222, 223, 224, 224, 225, 225, 226, 226, 227, 227, 228, 229, 229, 230,
-230, 231, 231, 232, 232, 233, 234, 234, 235, 235, 236, 236, 237, 237, 238, 238,
-239, 240, 240, 241, 241, 242, 242, 243, 243, 244, 244, 245, 245, 246, 246, 247,
-247, 248, 248, 249, 249, 250, 250, 251, 251, 252, 252, 253, 253, 254, 254, 255
-};
-
-static INLINE
-int
-ss_isqrt(int x) {
-  int y, e;
-
-  if(x >= (SS_BLOCKSIZE * SS_BLOCKSIZE)) { return SS_BLOCKSIZE; }
-  e = (x & 0xffff0000) ?
-        ((x & 0xff000000) ?
-          24 + lg_table[(x >> 24) & 0xff] :
-          16 + lg_table[(x >> 16) & 0xff]) :
-        ((x & 0x0000ff00) ?
-           8 + lg_table[(x >>  8) & 0xff] :
-           0 + lg_table[(x >>  0) & 0xff]);
-
-  if(e >= 16) {
-    y = sqq_table[x >> ((e - 6) - (e & 1))] << ((e >> 1) - 7);
-    if(e >= 24) { y = (y + 1 + x / y) >> 1; }
-    y = (y + 1 + x / y) >> 1;
-  } else if(e >= 8) {
-    y = (sqq_table[x >> ((e - 6) - (e & 1))] >> (7 - (e >> 1))) + 1;
-  } else {
-    return sqq_table[x] >> 4;
-  }
-
-  return (x < (y * y)) ? y - 1 : y;
-}
-
-#endif /* SS_BLOCKSIZE != 0 */
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Compares two suffixes. */
-static INLINE
-int
-ss_compare(const unsigned char *T,
-           const int *p1, const int *p2,
-           int depth) {
-  const unsigned char *U1, *U2, *U1n, *U2n;
-
-  for(U1 = T + depth + *p1,
-      U2 = T + depth + *p2,
-      U1n = T + *(p1 + 1) + 2,
-      U2n = T + *(p2 + 1) + 2;
-      (U1 < U1n) && (U2 < U2n) && (*U1 == *U2);
-      ++U1, ++U2) {
-  }
-
-  return U1 < U1n ?
-        (U2 < U2n ? *U1 - *U2 : 1) :
-        (U2 < U2n ? -1 : 0);
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-#if (SS_BLOCKSIZE != 1) && (SS_INSERTIONSORT_THRESHOLD != 1)
-
-/* Insertionsort for small size groups */
-static
-void
-ss_insertionsort(const unsigned char *T, const int *PA,
-                 int *first, int *last, int depth) {
-  int *i, *j;
-  int t;
-  int r;
-
-  for(i = last - 2; first <= i; --i) {
-    for(t = *i, j = i + 1; 0 < (r = ss_compare(T, PA + t, PA + *j, depth));) {
-      do { *(j - 1) = *j; } while((++j < last) && (*j < 0));
-      if(last <= j) { break; }
-    }
-    if(r == 0) { *j = ~*j; }
-    *(j - 1) = t;
-  }
-}
-
-#endif /* (SS_BLOCKSIZE != 1) && (SS_INSERTIONSORT_THRESHOLD != 1) */
-
-
-/*---------------------------------------------------------------------------*/
-
-#if (SS_BLOCKSIZE == 0) || (SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE)
-
-static INLINE
-void
-ss_fixdown(const unsigned char *Td, const int *PA,
-           int *SA, int i, int size) {
-  int j, k;
-  int v;
-  int c, d, e;
-
-  for(v = SA[i], c = Td[PA[v]]; (j = 2 * i + 1) < size; SA[i] = SA[k], i = k) {
-    d = Td[PA[SA[k = j++]]];
-    if(d < (e = Td[PA[SA[j]]])) { k = j; d = e; }
-    if(d <= c) { break; }
-  }
-  SA[i] = v;
-}
-
-/* Simple top-down heapsort. */
-static
-void
-ss_heapsort(const unsigned char *Td, const int *PA, int *SA, int size) {
-  int i, m;
-  int t;
-
-  m = size;
-  if((size % 2) == 0) {
-    m--;
-    if(Td[PA[SA[m / 2]]] < Td[PA[SA[m]]]) { SWAP(SA[m], SA[m / 2]); }
-  }
-
-  for(i = m / 2 - 1; 0 <= i; --i) { ss_fixdown(Td, PA, SA, i, m); }
-  if((size % 2) == 0) { SWAP(SA[0], SA[m]); ss_fixdown(Td, PA, SA, 0, m); }
-  for(i = m - 1; 0 < i; --i) {
-    t = SA[0], SA[0] = SA[i];
-    ss_fixdown(Td, PA, SA, 0, i);
-    SA[i] = t;
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Returns the median of three elements. */
-static INLINE
-int *
-ss_median3(const unsigned char *Td, const int *PA,
-           int *v1, int *v2, int *v3) {
-  int *t;
-  if(Td[PA[*v1]] > Td[PA[*v2]]) { SWAP(v1, v2); }
-  if(Td[PA[*v2]] > Td[PA[*v3]]) {
-    if(Td[PA[*v1]] > Td[PA[*v3]]) { return v1; }
-    else { return v3; }
-  }
-  return v2;
-}
-
-/* Returns the median of five elements. */
-static INLINE
-int *
-ss_median5(const unsigned char *Td, const int *PA,
-           int *v1, int *v2, int *v3, int *v4, int *v5) {
-  int *t;
-  if(Td[PA[*v2]] > Td[PA[*v3]]) { SWAP(v2, v3); }
-  if(Td[PA[*v4]] > Td[PA[*v5]]) { SWAP(v4, v5); }
-  if(Td[PA[*v2]] > Td[PA[*v4]]) { SWAP(v2, v4); SWAP(v3, v5); }
-  if(Td[PA[*v1]] > Td[PA[*v3]]) { SWAP(v1, v3); }
-  if(Td[PA[*v1]] > Td[PA[*v4]]) { SWAP(v1, v4); SWAP(v3, v5); }
-  if(Td[PA[*v3]] > Td[PA[*v4]]) { return v4; }
-  return v3;
-}
-
-/* Returns the pivot element. */
-static INLINE
-int *
-ss_pivot(const unsigned char *Td, const int *PA, int *first, int *last) {
-  int *middle;
-  int t;
-
-  t = last - first;
-  middle = first + t / 2;
-
-  if(t <= 512) {
-    if(t <= 32) {
-      return ss_median3(Td, PA, first, middle, last - 1);
-    } else {
-      t >>= 2;
-      return ss_median5(Td, PA, first, first + t, middle, last - 1 - t, last - 1);
-    }
-  }
-  t >>= 3;
-  first  = ss_median3(Td, PA, first, first + t, first + (t << 1));
-  middle = ss_median3(Td, PA, middle - t, middle, middle + t);
-  last   = ss_median3(Td, PA, last - 1 - (t << 1), last - 1 - t, last - 1);
-  return ss_median3(Td, PA, first, middle, last);
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Binary partition for substrings. */
-static INLINE
-int *
-ss_partition(const int *PA,
-                    int *first, int *last, int depth) {
-  int *a, *b;
-  int t;
-  for(a = first - 1, b = last;;) {
-    for(; (++a < b) && ((PA[*a] + depth) >= (PA[*a + 1] + 1));) { *a = ~*a; }
-    for(; (a < --b) && ((PA[*b] + depth) <  (PA[*b + 1] + 1));) { }
-    if(b <= a) { break; }
-    t = ~*b;
-    *b = *a;
-    *a = t;
-  }
-  if(first < a) { *first = ~*first; }
-  return a;
-}
-
-/* Multikey introsort for medium size groups. */
-static
-void
-ss_mintrosort(const unsigned char *T, const int *PA,
-              int *first, int *last,
-              int depth) {
-#define STACK_SIZE SS_MISORT_STACKSIZE
-  struct { int *a, *b, c; int d; } stack[STACK_SIZE];
-  const unsigned char *Td;
-  int *a, *b, *c, *d, *e, *f;
-  int s, t;
-  int ssize;
-  int limit;
-  int v, x = 0;
-
-  for(ssize = 0, limit = ss_ilg(last - first);;) {
-
-    if((last - first) <= SS_INSERTIONSORT_THRESHOLD) {
-#if 1 < SS_INSERTIONSORT_THRESHOLD
-      if(1 < (last - first)) { ss_insertionsort(T, PA, first, last, depth); }
-#endif
-      STACK_POP(first, last, depth, limit);
-      continue;
-    }
-
-    Td = T + depth;
-    if(limit-- == 0) { ss_heapsort(Td, PA, first, last - first); }
-    if(limit < 0) {
-      for(a = first + 1, v = Td[PA[*first]]; a < last; ++a) {
-        if((x = Td[PA[*a]]) != v) {
-          if(1 < (a - first)) { break; }
-          v = x;
-          first = a;
-        }
-      }
-      if(Td[PA[*first] - 1] < v) {
-        first = ss_partition(PA, first, a, depth);
-      }
-      if((a - first) <= (last - a)) {
-        if(1 < (a - first)) {
-          STACK_PUSH(a, last, depth, -1);
-          last = a, depth += 1, limit = ss_ilg(a - first);
-        } else {
-          first = a, limit = -1;
-        }
-      } else {
-        if(1 < (last - a)) {
-          STACK_PUSH(first, a, depth + 1, ss_ilg(a - first));
-          first = a, limit = -1;
-        } else {
-          last = a, depth += 1, limit = ss_ilg(a - first);
-        }
-      }
-      continue;
-    }
-
-    /* choose pivot */
-    a = ss_pivot(Td, PA, first, last);
-    v = Td[PA[*a]];
-    SWAP(*first, *a);
-
-    /* partition */
-    for(b = first; (++b < last) && ((x = Td[PA[*b]]) == v);) { }
-    if(((a = b) < last) && (x < v)) {
-      for(; (++b < last) && ((x = Td[PA[*b]]) <= v);) {
-        if(x == v) { SWAP(*b, *a); ++a; }
-      }
-    }
-    for(c = last; (b < --c) && ((x = Td[PA[*c]]) == v);) { }
-    if((b < (d = c)) && (x > v)) {
-      for(; (b < --c) && ((x = Td[PA[*c]]) >= v);) {
-        if(x == v) { SWAP(*c, *d); --d; }
-      }
-    }
-    for(; b < c;) {
-      SWAP(*b, *c);
-      for(; (++b < c) && ((x = Td[PA[*b]]) <= v);) {
-        if(x == v) { SWAP(*b, *a); ++a; }
-      }
-      for(; (b < --c) && ((x = Td[PA[*c]]) >= v);) {
-        if(x == v) { SWAP(*c, *d); --d; }
-      }
-    }
-
-    if(a <= d) {
-      c = b - 1;
-
-      if((s = a - first) > (t = b - a)) { s = t; }
-      for(e = first, f = b - s; 0 < s; --s, ++e, ++f) { SWAP(*e, *f); }
-      if((s = d - c) > (t = last - d - 1)) { s = t; }
-      for(e = b, f = last - s; 0 < s; --s, ++e, ++f) { SWAP(*e, *f); }
-
-      a = first + (b - a), c = last - (d - c);
-      b = (v <= Td[PA[*a] - 1]) ? a : ss_partition(PA, a, c, depth);
-
-      if((a - first) <= (last - c)) {
-        if((last - c) <= (c - b)) {
-          STACK_PUSH(b, c, depth + 1, ss_ilg(c - b));
-          STACK_PUSH(c, last, depth, limit);
-          last = a;
-        } else if((a - first) <= (c - b)) {
-          STACK_PUSH(c, last, depth, limit);
-          STACK_PUSH(b, c, depth + 1, ss_ilg(c - b));
-          last = a;
-        } else {
-          STACK_PUSH(c, last, depth, limit);
-          STACK_PUSH(first, a, depth, limit);
-          first = b, last = c, depth += 1, limit = ss_ilg(c - b);
-        }
-      } else {
-        if((a - first) <= (c - b)) {
-          STACK_PUSH(b, c, depth + 1, ss_ilg(c - b));
-          STACK_PUSH(first, a, depth, limit);
-          first = c;
-        } else if((last - c) <= (c - b)) {
-          STACK_PUSH(first, a, depth, limit);
-          STACK_PUSH(b, c, depth + 1, ss_ilg(c - b));
-          first = c;
-        } else {
-          STACK_PUSH(first, a, depth, limit);
-          STACK_PUSH(c, last, depth, limit);
-          first = b, last = c, depth += 1, limit = ss_ilg(c - b);
-        }
-      }
-    } else {
-      limit += 1;
-      if(Td[PA[*first] - 1] < v) {
-        first = ss_partition(PA, first, last, depth);
-        limit = ss_ilg(last - first);
-      }
-      depth += 1;
-    }
-  }
-#undef STACK_SIZE
-}
-
-#endif /* (SS_BLOCKSIZE == 0) || (SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE) */
-
-
-/*---------------------------------------------------------------------------*/
-
-#if SS_BLOCKSIZE != 0
-
-static INLINE
-void
-ss_blockswap(int *a, int *b, int n) {
-  int t;
-  for(; 0 < n; --n, ++a, ++b) {
-    t = *a, *a = *b, *b = t;
-  }
-}
-
-static INLINE
-void
-ss_rotate(int *first, int *middle, int *last) {
-  int *a, *b, t;
-  int l, r;
-  l = middle - first, r = last - middle;
-  for(; (0 < l) && (0 < r);) {
-    if(l == r) { ss_blockswap(first, middle, l); break; }
-    if(l < r) {
-      a = last - 1, b = middle - 1;
-      t = *a;
-      do {
-        *a-- = *b, *b-- = *a;
-        if(b < first) {
-          *a = t;
-          last = a;
-          if((r -= l + 1) <= l) { break; }
-          a -= 1, b = middle - 1;
-          t = *a;
-        }
-      } while(1);
-    } else {
-      a = first, b = middle;
-      t = *a;
-      do {
-        *a++ = *b, *b++ = *a;
-        if(last <= b) {
-          *a = t;
-          first = a + 1;
-          if((l -= r + 1) <= r) { break; }
-          a += 1, b = middle;
-          t = *a;
-        }
-      } while(1);
-    }
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-static
-void
-ss_inplacemerge(const unsigned char *T, const int *PA,
-                int *first, int *middle, int *last,
-                int depth) {
-  const int *p;
-  int *a, *b;
-  int len, half;
-  int q, r;
-  int x;
-
-  for(;;) {
-    if(*(last - 1) < 0) { x = 1; p = PA + ~*(last - 1); }
-    else                { x = 0; p = PA +  *(last - 1); }
-    for(a = first, len = middle - first, half = len >> 1, r = -1;
-        0 < len;
-        len = half, half >>= 1) {
-      b = a + half;
-      q = ss_compare(T, PA + ((0 <= *b) ? *b : ~*b), p, depth);
-      if(q < 0) {
-        a = b + 1;
-        half -= (len & 1) ^ 1;
-      } else {
-        r = q;
-      }
-    }
-    if(a < middle) {
-      if(r == 0) { *a = ~*a; }
-      ss_rotate(a, middle, last);
-      last -= middle - a;
-      middle = a;
-      if(first == middle) { break; }
-    }
-    --last;
-    if(x != 0) { while(*--last < 0) { } }
-    if(middle == last) { break; }
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Merge-forward with internal buffer. */
-static
-void
-ss_mergeforward(const unsigned char *T, const int *PA,
-                int *first, int *middle, int *last,
-                int *buf, int depth) {
-  int *a, *b, *c, *bufend;
-  int t;
-  int r;
-
-  bufend = buf + (middle - first) - 1;
-  ss_blockswap(buf, first, middle - first);
-
-  for(t = *(a = first), b = buf, c = middle;;) {
-    r = ss_compare(T, PA + *b, PA + *c, depth);
-    if(r < 0) {
-      do {
-        *a++ = *b;
-        if(bufend <= b) { *bufend = t; return; }
-        *b++ = *a;
-      } while(*b < 0);
-    } else if(r > 0) {
-      do {
-        *a++ = *c, *c++ = *a;
-        if(last <= c) {
-          while(b < bufend) { *a++ = *b, *b++ = *a; }
-          *a = *b, *b = t;
-          return;
-        }
-      } while(*c < 0);
-    } else {
-      *c = ~*c;
-      do {
-        *a++ = *b;
-        if(bufend <= b) { *bufend = t; return; }
-        *b++ = *a;
-      } while(*b < 0);
-
-      do {
-        *a++ = *c, *c++ = *a;
-        if(last <= c) {
-          while(b < bufend) { *a++ = *b, *b++ = *a; }
-          *a = *b, *b = t;
-          return;
-        }
-      } while(*c < 0);
-    }
-  }
-}
-
-/* Merge-backward with internal buffer. */
-static
-void
-ss_mergebackward(const unsigned char *T, const int *PA,
-                 int *first, int *middle, int *last,
-                 int *buf, int depth) {
-  const int *p1, *p2;
-  int *a, *b, *c, *bufend;
-  int t;
-  int r;
-  int x;
-
-  bufend = buf + (last - middle) - 1;
-  ss_blockswap(buf, middle, last - middle);
-
-  x = 0;
-  if(*bufend < 0)       { p1 = PA + ~*bufend; x |= 1; }
-  else                  { p1 = PA +  *bufend; }
-  if(*(middle - 1) < 0) { p2 = PA + ~*(middle - 1); x |= 2; }
-  else                  { p2 = PA +  *(middle - 1); }
-  for(t = *(a = last - 1), b = bufend, c = middle - 1;;) {
-    r = ss_compare(T, p1, p2, depth);
-    if(0 < r) {
-      if(x & 1) { do { *a-- = *b, *b-- = *a; } while(*b < 0); x ^= 1; }
-      *a-- = *b;
-      if(b <= buf) { *buf = t; break; }
-      *b-- = *a;
-      if(*b < 0) { p1 = PA + ~*b; x |= 1; }
-      else       { p1 = PA +  *b; }
-    } else if(r < 0) {
-      if(x & 2) { do { *a-- = *c, *c-- = *a; } while(*c < 0); x ^= 2; }
-      *a-- = *c, *c-- = *a;
-      if(c < first) {
-        while(buf < b) { *a-- = *b, *b-- = *a; }
-        *a = *b, *b = t;
-        break;
-      }
-      if(*c < 0) { p2 = PA + ~*c; x |= 2; }
-      else       { p2 = PA +  *c; }
-    } else {
-      if(x & 1) { do { *a-- = *b, *b-- = *a; } while(*b < 0); x ^= 1; }
-      *a-- = ~*b;
-      if(b <= buf) { *buf = t; break; }
-      *b-- = *a;
-      if(x & 2) { do { *a-- = *c, *c-- = *a; } while(*c < 0); x ^= 2; }
-      *a-- = *c, *c-- = *a;
-      if(c < first) {
-        while(buf < b) { *a-- = *b, *b-- = *a; }
-        *a = *b, *b = t;
-        break;
-      }
-      if(*b < 0) { p1 = PA + ~*b; x |= 1; }
-      else       { p1 = PA +  *b; }
-      if(*c < 0) { p2 = PA + ~*c; x |= 2; }
-      else       { p2 = PA +  *c; }
-    }
-  }
-}
-
-/* D&C based merge. */
-static
-void
-ss_swapmerge(const unsigned char *T, const int *PA,
-             int *first, int *middle, int *last,
-             int *buf, int bufsize, int depth) {
-#define STACK_SIZE SS_SMERGE_STACKSIZE
-#define GETIDX(a) ((0 <= (a)) ? (a) : (~(a)))
-#define MERGE_CHECK(a, b, c)\
-  do {\
-    if(((c) & 1) ||\
-       (((c) & 2) && (ss_compare(T, PA + GETIDX(*((a) - 1)), PA + *(a), depth) == 0))) {\
-      *(a) = ~*(a);\
-    }\
-    if(((c) & 4) && ((ss_compare(T, PA + GETIDX(*((b) - 1)), PA + *(b), depth) == 0))) {\
-      *(b) = ~*(b);\
-    }\
-  } while(0)
-  struct { int *a, *b, *c; int d; } stack[STACK_SIZE];
-  int *l, *r, *lm, *rm;
-  int m, len, half;
-  int ssize;
-  int check, next;
-
-  for(check = 0, ssize = 0;;) {
-    if((last - middle) <= bufsize) {
-      if((first < middle) && (middle < last)) {
-        ss_mergebackward(T, PA, first, middle, last, buf, depth);
-      }
-      MERGE_CHECK(first, last, check);
-      STACK_POP(first, middle, last, check);
-      continue;
-    }
-
-    if((middle - first) <= bufsize) {
-      if(first < middle) {
-        ss_mergeforward(T, PA, first, middle, last, buf, depth);
-      }
-      MERGE_CHECK(first, last, check);
-      STACK_POP(first, middle, last, check);
-      continue;
-    }
-
-    for(m = 0, len = MIN(middle - first, last - middle), half = len >> 1;
-        0 < len;
-        len = half, half >>= 1) {
-      if(ss_compare(T, PA + GETIDX(*(middle + m + half)),
-                       PA + GETIDX(*(middle - m - half - 1)), depth) < 0) {
-        m += half + 1;
-        half -= (len & 1) ^ 1;
-      }
-    }
-
-    if(0 < m) {
-      lm = middle - m, rm = middle + m;
-      ss_blockswap(lm, middle, m);
-      l = r = middle, next = 0;
-      if(rm < last) {
-        if(*rm < 0) {
-          *rm = ~*rm;
-          if(first < lm) { for(; *--l < 0;) { } next |= 4; }
-          next |= 1;
-        } else if(first < lm) {
-          for(; *r < 0; ++r) { }
-          next |= 2;
-        }
-      }
-
-      if((l - first) <= (last - r)) {
-        STACK_PUSH(r, rm, last, (next & 3) | (check & 4));
-        middle = lm, last = l, check = (check & 3) | (next & 4);
-      } else {
-        if((next & 2) && (r == middle)) { next ^= 6; }
-        STACK_PUSH(first, lm, l, (check & 3) | (next & 4));
-        first = r, middle = rm, check = (next & 3) | (check & 4);
-      }
-    } else {
-      if(ss_compare(T, PA + GETIDX(*(middle - 1)), PA + *middle, depth) == 0) {
-        *middle = ~*middle;
-      }
-      MERGE_CHECK(first, last, check);
-      STACK_POP(first, middle, last, check);
-    }
-  }
-#undef STACK_SIZE
-}
-
-#endif /* SS_BLOCKSIZE != 0 */
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Substring sort */
-static
-void
-sssort(const unsigned char *T, const int *PA,
-       int *first, int *last,
-       int *buf, int bufsize,
-       int depth, int n, int lastsuffix) {
-  int *a;
-#if SS_BLOCKSIZE != 0
-  int *b, *middle, *curbuf;
-  int j, k, curbufsize, limit;
-#endif
-  int i;
-
-  if(lastsuffix != 0) { ++first; }
-
-#if SS_BLOCKSIZE == 0
-  ss_mintrosort(T, PA, first, last, depth);
-#else
-  if((bufsize < SS_BLOCKSIZE) &&
-      (bufsize < (last - first)) &&
-      (bufsize < (limit = ss_isqrt(last - first)))) {
-    if(SS_BLOCKSIZE < limit) { limit = SS_BLOCKSIZE; }
-    buf = middle = last - limit, bufsize = limit;
-  } else {
-    middle = last, limit = 0;
-  }
-  for(a = first, i = 0; SS_BLOCKSIZE < (middle - a); a += SS_BLOCKSIZE, ++i) {
-#if SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE
-    ss_mintrosort(T, PA, a, a + SS_BLOCKSIZE, depth);
-#elif 1 < SS_BLOCKSIZE
-    ss_insertionsort(T, PA, a, a + SS_BLOCKSIZE, depth);
-#endif
-    curbufsize = last - (a + SS_BLOCKSIZE);
-    curbuf = a + SS_BLOCKSIZE;
-    if(curbufsize <= bufsize) { curbufsize = bufsize, curbuf = buf; }
-    for(b = a, k = SS_BLOCKSIZE, j = i; j & 1; b -= k, k <<= 1, j >>= 1) {
-      ss_swapmerge(T, PA, b - k, b, b + k, curbuf, curbufsize, depth);
-    }
-  }
-#if SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE
-  ss_mintrosort(T, PA, a, middle, depth);
-#elif 1 < SS_BLOCKSIZE
-  ss_insertionsort(T, PA, a, middle, depth);
-#endif
-  for(k = SS_BLOCKSIZE; i != 0; k <<= 1, i >>= 1) {
-    if(i & 1) {
-      ss_swapmerge(T, PA, a - k, a, middle, buf, bufsize, depth);
-      a -= k;
-    }
-  }
-  if(limit != 0) {
-#if SS_INSERTIONSORT_THRESHOLD < SS_BLOCKSIZE
-    ss_mintrosort(T, PA, middle, last, depth);
-#elif 1 < SS_BLOCKSIZE
-    ss_insertionsort(T, PA, middle, last, depth);
-#endif
-    ss_inplacemerge(T, PA, first, middle, last, depth);
-  }
-#endif
-
-  if(lastsuffix != 0) {
-    /* Insert last type B* suffix. */
-    int PAi[2]; PAi[0] = PA[*(first - 1)], PAi[1] = n - 2;
-    for(a = first, i = *(first - 1);
-        (a < last) && ((*a < 0) || (0 < ss_compare(T, &(PAi[0]), PA + *a, depth)));
-        ++a) {
-      *(a - 1) = *a;
-    }
-    *(a - 1) = i;
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-static INLINE
-int
-tr_ilg(int n) {
-  return (n & 0xffff0000) ?
-          ((n & 0xff000000) ?
-            24 + lg_table[(n >> 24) & 0xff] :
-            16 + lg_table[(n >> 16) & 0xff]) :
-          ((n & 0x0000ff00) ?
-             8 + lg_table[(n >>  8) & 0xff] :
-             0 + lg_table[(n >>  0) & 0xff]);
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Simple insertionsort for small size groups. */
-static
-void
-tr_insertionsort(const int *ISAd, int *first, int *last) {
-  int *a, *b;
-  int t, r;
-
-  for(a = first + 1; a < last; ++a) {
-    for(t = *a, b = a - 1; 0 > (r = ISAd[t] - ISAd[*b]);) {
-      do { *(b + 1) = *b; } while((first <= --b) && (*b < 0));
-      if(b < first) { break; }
-    }
-    if(r == 0) { *b = ~*b; }
-    *(b + 1) = t;
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-static INLINE
-void
-tr_fixdown(const int *ISAd, int *SA, int i, int size) {
-  int j, k;
-  int v;
-  int c, d, e;
-
-  for(v = SA[i], c = ISAd[v]; (j = 2 * i + 1) < size; SA[i] = SA[k], i = k) {
-    d = ISAd[SA[k = j++]];
-    if(d < (e = ISAd[SA[j]])) { k = j; d = e; }
-    if(d <= c) { break; }
-  }
-  SA[i] = v;
-}
-
-/* Simple top-down heapsort. */
-static
-void
-tr_heapsort(const int *ISAd, int *SA, int size) {
-  int i, m;
-  int t;
-
-  m = size;
-  if((size % 2) == 0) {
-    m--;
-    if(ISAd[SA[m / 2]] < ISAd[SA[m]]) { SWAP(SA[m], SA[m / 2]); }
-  }
-
-  for(i = m / 2 - 1; 0 <= i; --i) { tr_fixdown(ISAd, SA, i, m); }
-  if((size % 2) == 0) { SWAP(SA[0], SA[m]); tr_fixdown(ISAd, SA, 0, m); }
-  for(i = m - 1; 0 < i; --i) {
-    t = SA[0], SA[0] = SA[i];
-    tr_fixdown(ISAd, SA, 0, i);
-    SA[i] = t;
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Returns the median of three elements. */
-static INLINE
-int *
-tr_median3(const int *ISAd, int *v1, int *v2, int *v3) {
-  int *t;
-  if(ISAd[*v1] > ISAd[*v2]) { SWAP(v1, v2); }
-  if(ISAd[*v2] > ISAd[*v3]) {
-    if(ISAd[*v1] > ISAd[*v3]) { return v1; }
-    else { return v3; }
-  }
-  return v2;
-}
-
-/* Returns the median of five elements. */
-static INLINE
-int *
-tr_median5(const int *ISAd,
-           int *v1, int *v2, int *v3, int *v4, int *v5) {
-  int *t;
-  if(ISAd[*v2] > ISAd[*v3]) { SWAP(v2, v3); }
-  if(ISAd[*v4] > ISAd[*v5]) { SWAP(v4, v5); }
-  if(ISAd[*v2] > ISAd[*v4]) { SWAP(v2, v4); SWAP(v3, v5); }
-  if(ISAd[*v1] > ISAd[*v3]) { SWAP(v1, v3); }
-  if(ISAd[*v1] > ISAd[*v4]) { SWAP(v1, v4); SWAP(v3, v5); }
-  if(ISAd[*v3] > ISAd[*v4]) { return v4; }
-  return v3;
-}
-
-/* Returns the pivot element. */
-static INLINE
-int *
-tr_pivot(const int *ISAd, int *first, int *last) {
-  int *middle;
-  int t;
-
-  t = last - first;
-  middle = first + t / 2;
-
-  if(t <= 512) {
-    if(t <= 32) {
-      return tr_median3(ISAd, first, middle, last - 1);
-    } else {
-      t >>= 2;
-      return tr_median5(ISAd, first, first + t, middle, last - 1 - t, last - 1);
-    }
-  }
-  t >>= 3;
-  first  = tr_median3(ISAd, first, first + t, first + (t << 1));
-  middle = tr_median3(ISAd, middle - t, middle, middle + t);
-  last   = tr_median3(ISAd, last - 1 - (t << 1), last - 1 - t, last - 1);
-  return tr_median3(ISAd, first, middle, last);
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-typedef struct _trbudget_t trbudget_t;
-struct _trbudget_t {
-  int chance;
-  int remain;
-  int incval;
-  int count;
-};
-
-static INLINE
-void
-trbudget_init(trbudget_t *budget, int chance, int incval) {
-  budget->chance = chance;
-  budget->remain = budget->incval = incval;
-}
-
-static INLINE
-int
-trbudget_check(trbudget_t *budget, int size) {
-  if(size <= budget->remain) { budget->remain -= size; return 1; }
-  if(budget->chance == 0) { budget->count += size; return 0; }
-  budget->remain += budget->incval - size;
-  budget->chance -= 1;
-  return 1;
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-static INLINE
-void
-tr_partition(const int *ISAd,
-             int *first, int *middle, int *last,
-             int **pa, int **pb, int v) {
-  int *a, *b, *c, *d, *e, *f;
-  int t, s;
-  int x = 0;
-
-  for(b = middle - 1; (++b < last) && ((x = ISAd[*b]) == v);) { }
-  if(((a = b) < last) && (x < v)) {
-    for(; (++b < last) && ((x = ISAd[*b]) <= v);) {
-      if(x == v) { SWAP(*b, *a); ++a; }
-    }
-  }
-  for(c = last; (b < --c) && ((x = ISAd[*c]) == v);) { }
-  if((b < (d = c)) && (x > v)) {
-    for(; (b < --c) && ((x = ISAd[*c]) >= v);) {
-      if(x == v) { SWAP(*c, *d); --d; }
-    }
-  }
-  for(; b < c;) {
-    SWAP(*b, *c);
-    for(; (++b < c) && ((x = ISAd[*b]) <= v);) {
-      if(x == v) { SWAP(*b, *a); ++a; }
-    }
-    for(; (b < --c) && ((x = ISAd[*c]) >= v);) {
-      if(x == v) { SWAP(*c, *d); --d; }
-    }
-  }
-
-  if(a <= d) {
-    c = b - 1;
-    if((s = a - first) > (t = b - a)) { s = t; }
-    for(e = first, f = b - s; 0 < s; --s, ++e, ++f) { SWAP(*e, *f); }
-    if((s = d - c) > (t = last - d - 1)) { s = t; }
-    for(e = b, f = last - s; 0 < s; --s, ++e, ++f) { SWAP(*e, *f); }
-    first += (b - a), last -= (d - c);
-  }
-  *pa = first, *pb = last;
-}
-
-static
-void
-tr_copy(int *ISA, const int *SA,
-        int *first, int *a, int *b, int *last,
-        int depth) {
-  /* sort suffixes of middle partition
-     by using sorted order of suffixes of left and right partition. */
-  int *c, *d, *e;
-  int s, v;
-
-  v = b - SA - 1;
-  for(c = first, d = a - 1; c <= d; ++c) {
-    if((0 <= (s = *c - depth)) && (ISA[s] == v)) {
-      *++d = s;
-      ISA[s] = d - SA;
-    }
-  }
-  for(c = last - 1, e = d + 1, d = b; e < d; --c) {
-    if((0 <= (s = *c - depth)) && (ISA[s] == v)) {
-      *--d = s;
-      ISA[s] = d - SA;
-    }
-  }
-}
-
-static
-void
-tr_partialcopy(int *ISA, const int *SA,
-               int *first, int *a, int *b, int *last,
-               int depth) {
-  int *c, *d, *e;
-  int s, v;
-  int rank, lastrank, newrank = -1;
-
-  v = b - SA - 1;
-  lastrank = -1;
-  for(c = first, d = a - 1; c <= d; ++c) {
-    if((0 <= (s = *c - depth)) && (ISA[s] == v)) {
-      *++d = s;
-      rank = ISA[s + depth];
-      if(lastrank != rank) { lastrank = rank; newrank = d - SA; }
-      ISA[s] = newrank;
-    }
-  }
-
-  lastrank = -1;
-  for(e = d; first <= e; --e) {
-    rank = ISA[*e];
-    if(lastrank != rank) { lastrank = rank; newrank = e - SA; }
-    if(newrank != rank) { ISA[*e] = newrank; }
-  }
-
-  lastrank = -1;
-  for(c = last - 1, e = d + 1, d = b; e < d; --c) {
-    if((0 <= (s = *c - depth)) && (ISA[s] == v)) {
-      *--d = s;
-      rank = ISA[s + depth];
-      if(lastrank != rank) { lastrank = rank; newrank = d - SA; }
-      ISA[s] = newrank;
-    }
-  }
-}
-
-static
-void
-tr_introsort(int *ISA, const int *ISAd,
-             int *SA, int *first, int *last,
-             trbudget_t *budget) {
-#define STACK_SIZE TR_STACKSIZE
-  struct { const int *a; int *b, *c; int d, e; }stack[STACK_SIZE];
-  int *a, *b, *c;
-  int t;
-  int v, x = 0;
-  int incr = ISAd - ISA;
-  int limit, next;
-  int ssize, trlink = -1;
-
-  for(ssize = 0, limit = tr_ilg(last - first);;) {
-
-    if(limit < 0) {
-      if(limit == -1) {
-        /* tandem repeat partition */
-        tr_partition(ISAd - incr, first, first, last, &a, &b, last - SA - 1);
-
-        /* update ranks */
-        if(a < last) {
-          for(c = first, v = a - SA - 1; c < a; ++c) { ISA[*c] = v; }
-        }
-        if(b < last) {
-          for(c = a, v = b - SA - 1; c < b; ++c) { ISA[*c] = v; }
-        }
-
-        /* push */
-        if(1 < (b - a)) {
-          STACK_PUSH5(NULL, a, b, 0, 0);
-          STACK_PUSH5(ISAd - incr, first, last, -2, trlink);
-          trlink = ssize - 2;
-        }
-        if((a - first) <= (last - b)) {
-          if(1 < (a - first)) {
-            STACK_PUSH5(ISAd, b, last, tr_ilg(last - b), trlink);
-            last = a, limit = tr_ilg(a - first);
-          } else if(1 < (last - b)) {
-            first = b, limit = tr_ilg(last - b);
-          } else {
-            STACK_POP5(ISAd, first, last, limit, trlink);
-          }
-        } else {
-          if(1 < (last - b)) {
-            STACK_PUSH5(ISAd, first, a, tr_ilg(a - first), trlink);
-            first = b, limit = tr_ilg(last - b);
-          } else if(1 < (a - first)) {
-            last = a, limit = tr_ilg(a - first);
-          } else {
-            STACK_POP5(ISAd, first, last, limit, trlink);
-          }
-        }
-      } else if(limit == -2) {
-        /* tandem repeat copy */
-        a = stack[--ssize].b, b = stack[ssize].c;
-        if(stack[ssize].d == 0) {
-          tr_copy(ISA, SA, first, a, b, last, ISAd - ISA);
-        } else {
-          if(0 <= trlink) { stack[trlink].d = -1; }
-          tr_partialcopy(ISA, SA, first, a, b, last, ISAd - ISA);
-        }
-        STACK_POP5(ISAd, first, last, limit, trlink);
-      } else {
-        /* sorted partition */
-        if(0 <= *first) {
-          a = first;
-          do { ISA[*a] = a - SA; } while((++a < last) && (0 <= *a));
-          first = a;
-        }
-        if(first < last) {
-          a = first; do { *a = ~*a; } while(*++a < 0);
-          next = (ISA[*a] != ISAd[*a]) ? tr_ilg(a - first + 1) : -1;
-          if(++a < last) { for(b = first, v = a - SA - 1; b < a; ++b) { ISA[*b] = v; } }
-
-          /* push */
-          if(trbudget_check(budget, a - first)) {
-            if((a - first) <= (last - a)) {
-              STACK_PUSH5(ISAd, a, last, -3, trlink);
-              ISAd += incr, last = a, limit = next;
-            } else {
-              if(1 < (last - a)) {
-                STACK_PUSH5(ISAd + incr, first, a, next, trlink);
-                first = a, limit = -3;
-              } else {
-                ISAd += incr, last = a, limit = next;
-              }
-            }
-          } else {
-            if(0 <= trlink) { stack[trlink].d = -1; }
-            if(1 < (last - a)) {
-              first = a, limit = -3;
-            } else {
-              STACK_POP5(ISAd, first, last, limit, trlink);
-            }
-          }
-        } else {
-          STACK_POP5(ISAd, first, last, limit, trlink);
-        }
-      }
-      continue;
-    }
-
-    if((last - first) <= TR_INSERTIONSORT_THRESHOLD) {
-      tr_insertionsort(ISAd, first, last);
-      limit = -3;
-      continue;
-    }
-
-    if(limit-- == 0) {
-      tr_heapsort(ISAd, first, last - first);
-      for(a = last - 1; first < a; a = b) {
-        for(x = ISAd[*a], b = a - 1; (first <= b) && (ISAd[*b] == x); --b) { *b = ~*b; }
-      }
-      limit = -3;
-      continue;
-    }
-
-    /* choose pivot */
-    a = tr_pivot(ISAd, first, last);
-    SWAP(*first, *a);
-    v = ISAd[*first];
-
-    /* partition */
-    tr_partition(ISAd, first, first + 1, last, &a, &b, v);
-    if((last - first) != (b - a)) {
-      next = (ISA[*a] != v) ? tr_ilg(b - a) : -1;
-
-      /* update ranks */
-      for(c = first, v = a - SA - 1; c < a; ++c) { ISA[*c] = v; }
-      if(b < last) { for(c = a, v = b - SA - 1; c < b; ++c) { ISA[*c] = v; } }
-
-      /* push */
-      if((1 < (b - a)) && (trbudget_check(budget, b - a))) {
-        if((a - first) <= (last - b)) {
-          if((last - b) <= (b - a)) {
-            if(1 < (a - first)) {
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              STACK_PUSH5(ISAd, b, last, limit, trlink);
-              last = a;
-            } else if(1 < (last - b)) {
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              first = b;
-            } else {
-              ISAd += incr, first = a, last = b, limit = next;
-            }
-          } else if((a - first) <= (b - a)) {
-            if(1 < (a - first)) {
-              STACK_PUSH5(ISAd, b, last, limit, trlink);
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              last = a;
-            } else {
-              STACK_PUSH5(ISAd, b, last, limit, trlink);
-              ISAd += incr, first = a, last = b, limit = next;
-            }
-          } else {
-            STACK_PUSH5(ISAd, b, last, limit, trlink);
-            STACK_PUSH5(ISAd, first, a, limit, trlink);
-            ISAd += incr, first = a, last = b, limit = next;
-          }
-        } else {
-          if((a - first) <= (b - a)) {
-            if(1 < (last - b)) {
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              STACK_PUSH5(ISAd, first, a, limit, trlink);
-              first = b;
-            } else if(1 < (a - first)) {
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              last = a;
-            } else {
-              ISAd += incr, first = a, last = b, limit = next;
-            }
-          } else if((last - b) <= (b - a)) {
-            if(1 < (last - b)) {
-              STACK_PUSH5(ISAd, first, a, limit, trlink);
-              STACK_PUSH5(ISAd + incr, a, b, next, trlink);
-              first = b;
-            } else {
-              STACK_PUSH5(ISAd, first, a, limit, trlink);
-              ISAd += incr, first = a, last = b, limit = next;
-            }
-          } else {
-            STACK_PUSH5(ISAd, first, a, limit, trlink);
-            STACK_PUSH5(ISAd, b, last, limit, trlink);
-            ISAd += incr, first = a, last = b, limit = next;
-          }
-        }
-      } else {
-        if((1 < (b - a)) && (0 <= trlink)) { stack[trlink].d = -1; }
-        if((a - first) <= (last - b)) {
-          if(1 < (a - first)) {
-            STACK_PUSH5(ISAd, b, last, limit, trlink);
-            last = a;
-          } else if(1 < (last - b)) {
-            first = b;
-          } else {
-            STACK_POP5(ISAd, first, last, limit, trlink);
-          }
-        } else {
-          if(1 < (last - b)) {
-            STACK_PUSH5(ISAd, first, a, limit, trlink);
-            first = b;
-          } else if(1 < (a - first)) {
-            last = a;
-          } else {
-            STACK_POP5(ISAd, first, last, limit, trlink);
-          }
-        }
-      }
-    } else {
-      if(trbudget_check(budget, last - first)) {
-        limit = tr_ilg(last - first), ISAd += incr;
-      } else {
-        if(0 <= trlink) { stack[trlink].d = -1; }
-        STACK_POP5(ISAd, first, last, limit, trlink);
-      }
-    }
-  }
-#undef STACK_SIZE
-}
-
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Tandem repeat sort */
-static
-void
-trsort(int *ISA, int *SA, int n, int depth) {
-  int *ISAd;
-  int *first, *last;
-  trbudget_t budget;
-  int t, skip, unsorted;
-
-  trbudget_init(&budget, tr_ilg(n) * 2 / 3, n);
-/*  trbudget_init(&budget, tr_ilg(n) * 3 / 4, n); */
-  for(ISAd = ISA + depth; -n < *SA; ISAd += ISAd - ISA) {
-    first = SA;
-    skip = 0;
-    unsorted = 0;
-    do {
-      if((t = *first) < 0) { first -= t; skip += t; }
-      else {
-        if(skip != 0) { *(first + skip) = skip; skip = 0; }
-        last = SA + ISA[t] + 1;
-        if(1 < (last - first)) {
-          budget.count = 0;
-          tr_introsort(ISA, ISAd, SA, first, last, &budget);
-          if(budget.count != 0) { unsorted += budget.count; }
-          else { skip = first - last; }
-        } else if((last - first) == 1) {
-          skip = -1;
-        }
-        first = last;
-      }
-    } while(first < (SA + n));
-    if(skip != 0) { *(first + skip) = skip; }
-    if(unsorted == 0) { break; }
-  }
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/* Sorts suffixes of type B*. */
-static
-int
-sort_typeBstar(const unsigned char *T, int *SA,
-               int *bucket_A, int *bucket_B,
-               int n, int openMP) {
-  int *PAb, *ISAb, *buf;
-#ifdef LIBBSC_OPENMP
-  int *curbuf;
-  int l;
-#endif
-  int i, j, k, t, m, bufsize;
-  int c0, c1;
-#ifdef LIBBSC_OPENMP
-  int d0, d1;
-#endif
-  (void)openMP;
-
-  /* Initialize bucket arrays. */
-  for(i = 0; i < BUCKET_A_SIZE; ++i) { bucket_A[i] = 0; }
-  for(i = 0; i < BUCKET_B_SIZE; ++i) { bucket_B[i] = 0; }
-
-  /* Count the number of occurrences of the first one or two characters of each
-     type A, B and B* suffix. Moreover, store the beginning position of all
-     type B* suffixes into the array SA. */
-  for(i = n - 1, m = n, c0 = T[n - 1]; 0 <= i;) {
-    /* type A suffix. */
-    do { ++BUCKET_A(c1 = c0); } while((0 <= --i) && ((c0 = T[i]) >= c1));
-    if(0 <= i) {
-      /* type B* suffix. */
-      ++BUCKET_BSTAR(c0, c1);
-      SA[--m] = i;
-      /* type B suffix. */
-      for(--i, c1 = c0; (0 <= i) && ((c0 = T[i]) <= c1); --i, c1 = c0) {
-        ++BUCKET_B(c0, c1);
-      }
-    }
-  }
-  m = n - m;
-/*
-note:
-  A type B* suffix is lexicographically smaller than a type B suffix that
-  begins with the same first two characters.
-*/
-
-  /* Calculate the index of start/end point of each bucket. */
-  for(c0 = 0, i = 0, j = 0; c0 < ALPHABET_SIZE; ++c0) {
-    t = i + BUCKET_A(c0);
-    BUCKET_A(c0) = i + j; /* start point */
-    i = t + BUCKET_B(c0, c0);
-    for(c1 = c0 + 1; c1 < ALPHABET_SIZE; ++c1) {
-      j += BUCKET_BSTAR(c0, c1);
-      BUCKET_BSTAR(c0, c1) = j; /* end point */
-      i += BUCKET_B(c0, c1);
-    }
-  }
-
-  if(0 < m) {
-    /* Sort the type B* suffixes by their first two characters. */
-    PAb = SA + n - m; ISAb = SA + m;
-    for(i = m - 2; 0 <= i; --i) {
-      t = PAb[i], c0 = T[t], c1 = T[t + 1];
-      SA[--BUCKET_BSTAR(c0, c1)] = i;
-    }
-    t = PAb[m - 1], c0 = T[t], c1 = T[t + 1];
-    SA[--BUCKET_BSTAR(c0, c1)] = m - 1;
-
-    /* Sort the type B* substrings using sssort. */
-#ifdef LIBBSC_OPENMP
-    if (openMP)
-    {
-        buf = SA + m;
-        c0 = ALPHABET_SIZE - 2, c1 = ALPHABET_SIZE - 1, j = m;
-#pragma omp parallel default(shared) private(bufsize, curbuf, k, l, d0, d1)
-        {
-          bufsize = (n - (2 * m)) / omp_get_num_threads();
-          curbuf = buf + omp_get_thread_num() * bufsize;
-          k = 0;
-          for(;;) {
-            #pragma omp critical(sssort_lock)
-            {
-              if(0 < (l = j)) {
-                d0 = c0, d1 = c1;
-                do {
-                  k = BUCKET_BSTAR(d0, d1);
-                  if(--d1 <= d0) {
-                    d1 = ALPHABET_SIZE - 1;
-                    if(--d0 < 0) { break; }
-                  }
-                } while(((l - k) <= 1) && (0 < (l = k)));
-                c0 = d0, c1 = d1, j = k;
-              }
-            }
-            if(l == 0) { break; }
-            sssort(T, PAb, SA + k, SA + l,
-                   curbuf, bufsize, 2, n, *(SA + k) == (m - 1));
-          }
-        }
-    }
-    else
-    {
-        buf = SA + m, bufsize = n - (2 * m);
-        for(c0 = ALPHABET_SIZE - 2, j = m; 0 < j; --c0) {
-          for(c1 = ALPHABET_SIZE - 1; c0 < c1; j = i, --c1) {
-            i = BUCKET_BSTAR(c0, c1);
-            if(1 < (j - i)) {
-              sssort(T, PAb, SA + i, SA + j,
-                     buf, bufsize, 2, n, *(SA + i) == (m - 1));
-            }
-          }
-        }
-    }
-#else
-    buf = SA + m, bufsize = n - (2 * m);
-    for(c0 = ALPHABET_SIZE - 2, j = m; 0 < j; --c0) {
-      for(c1 = ALPHABET_SIZE - 1; c0 < c1; j = i, --c1) {
-        i = BUCKET_BSTAR(c0, c1);
-        if(1 < (j - i)) {
-          sssort(T, PAb, SA + i, SA + j,
-                 buf, bufsize, 2, n, *(SA + i) == (m - 1));
-        }
-      }
-    }
-#endif
-
-    /* Compute ranks of type B* substrings. */
-    for(i = m - 1; 0 <= i; --i) {
-      if(0 <= SA[i]) {
-        j = i;
-        do { ISAb[SA[i]] = i; } while((0 <= --i) && (0 <= SA[i]));
-        SA[i + 1] = i - j;
-        if(i <= 0) { break; }
-      }
-      j = i;
-      do { ISAb[SA[i] = ~SA[i]] = j; } while(SA[--i] < 0);
-      ISAb[SA[i]] = j;
-    }
-
-    /* Construct the inverse suffix array of type B* suffixes using trsort. */
-    trsort(ISAb, SA, m, 1);
-
-    /* Set the sorted order of type B* suffixes. */
-    for(i = n - 1, j = m, c0 = T[n - 1]; 0 <= i;) {
-      for(--i, c1 = c0; (0 <= i) && ((c0 = T[i]) >= c1); --i, c1 = c0) { }
-      if(0 <= i) {
-        t = i;
-        for(--i, c1 = c0; (0 <= i) && ((c0 = T[i]) <= c1); --i, c1 = c0) { }
-        SA[ISAb[--j]] = ((t == 0) || (1 < (t - i))) ? t : ~t;
-      }
-    }
-
-    /* Calculate the index of start/end point of each bucket. */
-    BUCKET_B(ALPHABET_SIZE - 1, ALPHABET_SIZE - 1) = n; /* end point */
-    for(c0 = ALPHABET_SIZE - 2, k = m - 1; 0 <= c0; --c0) {
-      i = BUCKET_A(c0 + 1) - 1;
-      for(c1 = ALPHABET_SIZE - 1; c0 < c1; --c1) {
-        t = i - BUCKET_B(c0, c1);
-        BUCKET_B(c0, c1) = i; /* end point */
-
-        /* Move all type B* suffixes to the correct position. */
-        for(i = t, j = BUCKET_BSTAR(c0, c1);
-            j <= k;
-            --i, --k) { SA[i] = SA[k]; }
-      }
-      BUCKET_BSTAR(c0, c0 + 1) = i - BUCKET_B(c0, c0) + 1; /* start point */
-      BUCKET_B(c0, c0) = i; /* end point */
-    }
-  }
-
-  return m;
-}
-
-/* Constructs the suffix array by using the sorted order of type B* suffixes. */
-static
-void
-construct_SA(const unsigned char *T, int *SA,
-             int *bucket_A, int *bucket_B,
-             int n, int m) {
-  int *i, *j, *k;
-  int s;
-  int c0, c1, c2;
-
-  if(0 < m) {
-    /* Construct the sorted order of type B suffixes by using
-       the sorted order of type B* suffixes. */
-    for(c1 = ALPHABET_SIZE - 2; 0 <= c1; --c1) {
-      /* Scan the suffix array from right to left. */
-      for(i = SA + BUCKET_BSTAR(c1, c1 + 1),
-          j = SA + BUCKET_A(c1 + 1) - 1, k = NULL, c2 = -1;
-          i <= j;
-          --j) {
-        if(0 < (s = *j)) {
-          assert(T[s] == c1);
-          assert(((s + 1) < n) && (T[s] <= T[s + 1]));
-          assert(T[s - 1] <= T[s]);
-          *j = ~s;
-          c0 = T[--s];
-          if((0 < s) && (T[s - 1] > c0)) { s = ~s; }
-          if(c0 != c2) {
-            if(0 <= c2) { BUCKET_B(c2, c1) = k - SA; }
-            k = SA + BUCKET_B(c2 = c0, c1);
-          }
-          assert(k < j); assert(k != NULL);
-          *k-- = s;
-        } else {
-          assert(((s == 0) && (T[s] == c1)) || (s < 0));
-          *j = ~s;
-        }
-      }
-    }
-  }
-
-  /* Construct the suffix array by using
-     the sorted order of type B suffixes. */
-  k = SA + BUCKET_A(c2 = T[n - 1]);
-  *k++ = (T[n - 2] < c2) ? ~(n - 1) : (n - 1);
-  /* Scan the suffix array from left to right. */
-  for(i = SA, j = SA + n; i < j; ++i) {
-    if(0 < (s = *i)) {
-      assert(T[s - 1] >= T[s]);
-      c0 = T[--s];
-      if((s == 0) || (T[s - 1] < c0)) { s = ~s; }
-      if(c0 != c2) {
-        BUCKET_A(c2) = k - SA;
-        k = SA + BUCKET_A(c2 = c0);
-      }
-      assert(i < k);
-      *k++ = s;
-    } else {
-      assert(s < 0);
-      *i = ~s;
-    }
-  }
-}
-
-/* Constructs the burrows-wheeler transformed string directly
-   by using the sorted order of type B* suffixes. */
-static
-int
-construct_BWT(const unsigned char *T, int *SA,
-              int *bucket_A, int *bucket_B,
-              int n, int m) {
-  int *i, *j, *k, *orig;
-  int s;
-  int c0, c1, c2;
-
-  if(0 < m) {
-    /* Construct the sorted order of type B suffixes by using
-       the sorted order of type B* suffixes. */
-    for(c1 = ALPHABET_SIZE - 2; 0 <= c1; --c1) {
-      /* Scan the suffix array from right to left. */
-      for(i = SA + BUCKET_BSTAR(c1, c1 + 1),
-          j = SA + BUCKET_A(c1 + 1) - 1, k = NULL, c2 = -1;
-          i <= j;
-          --j) {
-        if(0 < (s = *j)) {
-          assert(T[s] == c1);
-          assert(((s + 1) < n) && (T[s] <= T[s + 1]));
-          assert(T[s - 1] <= T[s]);
-          c0 = T[--s];
-          *j = ~((int)c0);
-          if((0 < s) && (T[s - 1] > c0)) { s = ~s; }
-          if(c0 != c2) {
-            if(0 <= c2) { BUCKET_B(c2, c1) = k - SA; }
-            k = SA + BUCKET_B(c2 = c0, c1);
-          }
-          assert(k < j); assert(k != NULL);
-          *k-- = s;
-        } else if(s != 0) {
-          *j = ~s;
-#ifndef NDEBUG
-        } else {
-          assert(T[s] == c1);
-#endif
-        }
-      }
-    }
-  }
-
-  /* Construct the BWTed string by using
-     the sorted order of type B suffixes. */
-  k = SA + BUCKET_A(c2 = T[n - 1]);
-  *k++ = (T[n - 2] < c2) ? ~((int)T[n - 2]) : (n - 1);
-  /* Scan the suffix array from left to right. */
-  for(i = SA, j = SA + n, orig = SA; i < j; ++i) {
-    if(0 < (s = *i)) {
-      assert(T[s - 1] >= T[s]);
-      c0 = T[--s];
-      *i = c0;
-      if((0 < s) && (T[s - 1] < c0)) { s = ~((int)T[s - 1]); }
-      if(c0 != c2) {
-        BUCKET_A(c2) = k - SA;
-        k = SA + BUCKET_A(c2 = c0);
-      }
-      assert(i < k);
-      *k++ = s;
-    } else if(s != 0) {
-      *i = ~s;
-    } else {
-      orig = i;
-    }
-  }
-
-  return orig - SA;
-}
-
-/* Constructs the burrows-wheeler transformed string directly
-   by using the sorted order of type B* suffixes. */
-static
-int
-construct_BWT_indexes(const unsigned char *T, int *SA,
-                      int *bucket_A, int *bucket_B,
-                      int n, int m,
-                      unsigned char * num_indexes, int * indexes) {
-  int *i, *j, *k, *orig;
-  int s;
-  int c0, c1, c2;
-
-  int mod = n / 8;
-  {
-      mod |= mod >> 1;  mod |= mod >> 2;
-      mod |= mod >> 4;  mod |= mod >> 8;
-      mod |= mod >> 16; mod >>= 1;
-
-      *num_indexes = (unsigned char)((n - 1) / (mod + 1));
-  }
-
-  if(0 < m) {
-    /* Construct the sorted order of type B suffixes by using
-       the sorted order of type B* suffixes. */
-    for(c1 = ALPHABET_SIZE - 2; 0 <= c1; --c1) {
-      /* Scan the suffix array from right to left. */
-      for(i = SA + BUCKET_BSTAR(c1, c1 + 1),
-          j = SA + BUCKET_A(c1 + 1) - 1, k = NULL, c2 = -1;
-          i <= j;
-          --j) {
-        if(0 < (s = *j)) {
-          assert(T[s] == c1);
-          assert(((s + 1) < n) && (T[s] <= T[s + 1]));
-          assert(T[s - 1] <= T[s]);
-
-          if ((s & mod) == 0) indexes[s / (mod + 1) - 1] = j - SA;
-
-          c0 = T[--s];
-          *j = ~((int)c0);
-          if((0 < s) && (T[s - 1] > c0)) { s = ~s; }
-          if(c0 != c2) {
-            if(0 <= c2) { BUCKET_B(c2, c1) = k - SA; }
-            k = SA + BUCKET_B(c2 = c0, c1);
-          }
-          assert(k < j); assert(k != NULL);
-          *k-- = s;
-        } else if(s != 0) {
-          *j = ~s;
-#ifndef NDEBUG
-        } else {
-          assert(T[s] == c1);
-#endif
-        }
-      }
-    }
-  }
-
-  /* Construct the BWTed string by using
-     the sorted order of type B suffixes. */
-  k = SA + BUCKET_A(c2 = T[n - 1]);
-  if (T[n - 2] < c2) {
-    if (((n - 1) & mod) == 0) indexes[(n - 1) / (mod + 1) - 1] = k - SA;
-    *k++ = ~((int)T[n - 2]);
-  }
-  else {
-    *k++ = n - 1;
-  }
-
-  /* Scan the suffix array from left to right. */
-  for(i = SA, j = SA + n, orig = SA; i < j; ++i) {
-    if(0 < (s = *i)) {
-      assert(T[s - 1] >= T[s]);
-
-      if ((s & mod) == 0) indexes[s / (mod + 1) - 1] = i - SA;
-
-      c0 = T[--s];
-      *i = c0;
-      if(c0 != c2) {
-        BUCKET_A(c2) = k - SA;
-        k = SA + BUCKET_A(c2 = c0);
-      }
-      assert(i < k);
-      if((0 < s) && (T[s - 1] < c0)) {
-          if ((s & mod) == 0) indexes[s / (mod + 1) - 1] = k - SA;
-          *k++ = ~((int)T[s - 1]);
-      } else
-        *k++ = s;
-    } else if(s != 0) {
-      *i = ~s;
-    } else {
-      orig = i;
-    }
-  }
-
-  return orig - SA;
-}
-
-
-/*---------------------------------------------------------------------------*/
-
-/*- Function -*/
-
-int
-divsufsort(const unsigned char *T, int *SA, int n, int openMP) {
-  int *bucket_A, *bucket_B;
-  int m;
-  int err = 0;
-
-  /* Check arguments. */
-  if((T == NULL) || (SA == NULL) || (n < 0)) { return -1; }
-  else if(n == 0) { return 0; }
-  else if(n == 1) { SA[0] = 0; return 0; }
-  else if(n == 2) { m = (T[0] < T[1]); SA[m ^ 1] = 0, SA[m] = 1; return 0; }
-
-  bucket_A = (int *)malloc(BUCKET_A_SIZE * sizeof(int));
-  bucket_B = (int *)malloc(BUCKET_B_SIZE * sizeof(int));
-
-  /* Suffixsort. */
-  if((bucket_A != NULL) && (bucket_B != NULL)) {
-    m = sort_typeBstar(T, SA, bucket_A, bucket_B, n, openMP);
-    construct_SA(T, SA, bucket_A, bucket_B, n, m);
-  } else {
-    err = -2;
-  }
-
-  free(bucket_B);
-  free(bucket_A);
-
-  return err;
-}
-
-int
-divbwt(const unsigned char *T, unsigned char *U, int *A, int n, unsigned char * num_indexes, int * indexes, int openMP) {
-  int *B;
-  int *bucket_A, *bucket_B;
-  int m, pidx, i;
-
-  /* Check arguments. */
-  if((T == NULL) || (U == NULL) || (n < 0)) { return -1; }
-  else if(n <= 1) { if(n == 1) { U[0] = T[0]; } return n; }
-
-  if((B = A) == NULL) { B = (int *)malloc((size_t)(n + 1) * sizeof(int)); }
-  bucket_A = (int *)malloc(BUCKET_A_SIZE * sizeof(int));
-  bucket_B = (int *)malloc(BUCKET_B_SIZE * sizeof(int));
-
-  /* Burrows-Wheeler Transform. */
-  if((B != NULL) && (bucket_A != NULL) && (bucket_B != NULL)) {
-    m = sort_typeBstar(T, B, bucket_A, bucket_B, n, openMP);
-
-    if (num_indexes == NULL || indexes == NULL) {
-        pidx = construct_BWT(T, B, bucket_A, bucket_B, n, m);
-    } else {
-        pidx = construct_BWT_indexes(T, B, bucket_A, bucket_B, n, m, num_indexes, indexes);
-    }
-
-    /* Copy to output string. */
-    U[0] = T[n - 1];
-    for(i = 0; i < pidx; ++i) { U[i + 1] = (unsigned char)B[i]; }
-    for(i += 1; i < n; ++i) { U[i] = (unsigned char)B[i]; }
-    pidx += 1;
-  } else {
-    pidx = -2;
-  }
-
-  free(bucket_B);
-  free(bucket_A);
-  if(A == NULL) { free(B); }
-
-  return pidx;
-}
@@ -71,7 +71,7 @@ RUST_TARGET_32 ?= i686-unknown-linux-gnu
 RUST_STATICLIB_32 := $(RUST_TARGET_DIR)/$(RUST_TARGET_32)/release/libzstd_rs.a
 RUST_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
                    --target-dir $(RUST_TARGET_DIR) --no-default-features
-RUST_CARGO_FLAGS += --features compression,decompression
+RUST_CARGO_FLAGS += --features compression,decompression,dict-builder
 ifneq ($(RUST_HUF_FEATURE),)
 RUST_CARGO_FLAGS += --features $(RUST_HUF_FEATURE)
 endif
@@ -96,7 +96,7 @@ $(RUST_CLI_STATICLIB): $(RUST_CLI_SOURCES)
 $(RUST_CLI_STATICLIB_32): $(RUST_CLI_SOURCES)
 	$(CARGO) build $(RUST_CLI_CARGO_FLAGS) --target $(RUST_TARGET_32)

-RUST_DECOMPRESS_BUILD_CONFIG := lib-c0-d1-$(RUST_BUILD_CONFIG)
+RUST_DECOMPRESS_BUILD_CONFIG := lib-c0-d1-b0-$(RUST_BUILD_CONFIG)
 RUST_DECOMPRESS_TARGET_DIR := $(RUST_DIR)/target/$(RUST_DECOMPRESS_BUILD_CONFIG)
 RUST_DECOMPRESS_STATICLIB := $(RUST_DECOMPRESS_TARGET_DIR)/release/libzstd_rs.a
 RUST_DECOMPRESS_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
@@ -119,7 +119,7 @@ RUST_DECOMPRESS_CLI_CARGO_FLAGS := --manifest-path $(RUST_CLI_MANIFEST) --releas
 $(RUST_DECOMPRESS_CLI_STATICLIB): $(RUST_CLI_SOURCES)
 	$(CARGO) build $(RUST_DECOMPRESS_CLI_CARGO_FLAGS)

-RUST_COMPRESS_BUILD_CONFIG := lib-c1-d0-$(RUST_BUILD_CONFIG)
+RUST_COMPRESS_BUILD_CONFIG := lib-c1-d0-b0-$(RUST_BUILD_CONFIG)
 RUST_COMPRESS_TARGET_DIR := $(RUST_DIR)/target/$(RUST_COMPRESS_BUILD_CONFIG)
 RUST_COMPRESS_STATICLIB := $(RUST_COMPRESS_TARGET_DIR)/release/libzstd_rs.a
 RUST_COMPRESS_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
@@ -129,6 +129,17 @@ RUST_COMPRESS_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
 $(RUST_COMPRESS_STATICLIB): $(RUST_SOURCES)
 	$(CARGO) build $(RUST_COMPRESS_CARGO_FLAGS)

+RUST_DICTBUILDER_BUILD_CONFIG := lib-c1-d0-b1-$(RUST_BUILD_CONFIG)
+RUST_DICTBUILDER_TARGET_DIR := $(RUST_DIR)/target/$(RUST_DICTBUILDER_BUILD_CONFIG)
+RUST_DICTBUILDER_STATICLIB := $(RUST_DICTBUILDER_TARGET_DIR)/release/libzstd_rs.a
+RUST_DICTBUILDER_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
+                                 --target-dir $(RUST_DICTBUILDER_TARGET_DIR) \
+                                 --no-default-features \
+                                 --features compression,dict-builder
+
+$(RUST_DICTBUILDER_STATICLIB): $(RUST_SOURCES)
+	$(CARGO) build $(RUST_DICTBUILDER_CARGO_FLAGS)
+
 RUST_COMPRESS_CLI_BUILD_CONFIG := cli-c1-d0-$(RUST_BUILD_CONFIG)
 RUST_COMPRESS_CLI_TARGET_DIR := $(RUST_DIR)/target/$(RUST_COMPRESS_CLI_BUILD_CONFIG)
 RUST_COMPRESS_CLI_STATICLIB := $(RUST_COMPRESS_CLI_TARGET_DIR)/release/libzstd_cli_rs.a
@@ -412,7 +423,7 @@ zstd-compress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) zstdcli.c util.c ti

 ## zstd-dictBuilder: executable supporting dictionary creation and compression (only)
 CLEAN += zstd-dictBuilder
-zstd-dictBuilder: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) $(ZDICT_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c dibio.c $(RUST_COMPRESS_STATICLIB) $(RUST_COMPRESS_CLI_STATICLIB)
+zstd-dictBuilder: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) $(ZDICT_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c dibio.c $(RUST_DICTBUILDER_STATICLIB) $(RUST_COMPRESS_CLI_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODECOMPRESS -DZSTD_NOTRACE $^ -o $@$(EXT)

 RUST_DIRECT_LINK_TARGETS := zstd32 zstd-nolegacy zstd-small zstd-frugal \
@@ -7,9 +7,10 @@ edition = "2021"
 crate-type = ["staticlib"]

 [features]
-default = ["compression", "decompression"]
+default = ["compression", "decompression", "dict-builder"]
 compression = []
 decompression = []
+dict-builder = []
 huf-force-decompress-x1 = []
 huf-force-decompress-x2 = []

@@ -48,6 +48,10 @@ zstd ABI:
    the dynamic-programming optimal parser itself remains in C for now.
  - `zstd_ldm` implements long-distance-match parameter selection, table
    maintenance, sequence generation, and sequence consumption.
+- Dictionary building
+  - `divsufsort` constructs the suffix array that drives the legacy `ZDICT`
+    trainer (`ZDICT_trainFromBuffer_legacy`).  The sample analysis and
+    dictionary assembly in `zdict.c`, `cover.c`, and `fastcover.c` remain C.
 - Runtime support
  - `threading` provides platform pthread wrappers required by zstd headers.
  - `pool` implements the bounded worker pool used by multithreaded compression.
@@ -66,10 +70,11 @@ zstd ABI:
    `fileio` backend still owns file opening, safe replacement, sparse writes,
    metadata, and streaming I/O.

-The optimal block matcher, high-level frame compression, dictionary-building,
-legacy decoding callbacks, and the CLI file-I/O backend are still C. They must
-move before the rewrite is complete. Keeping that boundary explicit prevents a
-passing hybrid build from being mistaken for the final all-Rust result.
+The optimal block matcher, high-level frame compression, dictionary-building
+except suffix-array construction, legacy decoding callbacks, and the CLI
+file-I/O backend are still C. They must move before the rewrite is complete.
+Keeping that boundary explicit prevents a passing hybrid build from being
+mistaken for the final all-Rust result.

 ## Compatibility boundary

@@ -80,8 +85,9 @@ makefile source list as a small shim so header configuration and platform
 preprocessor behavior stay available during the transition.

 The library, test, and program makefiles select an archive directory for the
-active C configuration: enabled compression/decompression modules, default or
-forced HUF X1/X2, and the matching Rust target for 32-bit C binaries. The
+active C configuration: enabled compression/decompression/dictionary-builder
+modules, default or forced HUF X1/X2, and the matching Rust target for 32-bit
+C binaries. The
 native static archive flattens Rust object members rather than nesting a Rust
 archive, while the native shared library retains all migrated Rust exports.
 When the HUF mode changes, the test and program paths also rebuild cached C
@@ -0,0 +1,2756 @@
+#![allow(clippy::missing_safety_doc)]
+#![allow(clippy::too_many_arguments)]
+
+//! Suffix-array construction for the dictionary builder.
+//!
+//! Port of `lib/dictBuilder/divsufsort.c` (libdivsufsort-lite, Copyright (c)
+//! 2003-2008 Yuta Mori, MIT license) in the exact configuration zstd compiles
+//! it with: `ALPHABET_SIZE = 256`, `SS_INSERTIONSORT_THRESHOLD = 8`,
+//! `SS_BLOCKSIZE = 1024`, and no OpenMP.  Only `divsufsort()` is exported;
+//! `divbwt()` has no callers anywhere in zstd and was not ported.
+//!
+//! The C implementation walks raw `int*` cursors through the caller's SA
+//! buffer, including transient one-before-the-range positions.  Every such
+//! cursor is translated to an `isize` index into one `&mut [i32]` slice
+//! covering the whole buffer, so all arithmetic — including the
+//! bitwise-complement rank marking and the C `int` value semantics — matches
+//! the original exactly while staying bounds-checked.
+
+use std::os::raw::c_int;
+use std::slice;
+
+const BUCKET_A_SIZE: usize = 256; /* ALPHABET_SIZE */
+const BUCKET_B_SIZE: usize = 256 * 256; /* ALPHABET_SIZE * ALPHABET_SIZE */
+const ALPHABET_SIZE: i32 = 256;
+const SS_INSERTIONSORT_THRESHOLD: isize = 8;
+const SS_BLOCKSIZE: isize = 1024;
+/* minstacksize = log(SS_BLOCKSIZE) / log(3) * 2 */
+const SS_MISORT_STACKSIZE: usize = 16;
+const SS_SMERGE_STACKSIZE: usize = 32;
+const TR_INSERTIONSORT_THRESHOLD: isize = 8;
+const TR_STACKSIZE: usize = 64;
+
+#[rustfmt::skip]
+static LG_TABLE: [i32; 256] = [
+ -1,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
+  5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
+  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+];
+
+#[rustfmt::skip]
+static SQQ_TABLE: [i32; 256] = [
+  0,  16,  22,  27,  32,  35,  39,  42,  45,  48,  50,  53,  55,  57,  59,  61,
+ 64,  65,  67,  69,  71,  73,  75,  76,  78,  80,  81,  83,  84,  86,  87,  89,
+ 90,  91,  93,  94,  96,  97,  98,  99, 101, 102, 103, 104, 106, 107, 108, 109,
+110, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126,
+128, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142,
+143, 144, 144, 145, 146, 147, 148, 149, 150, 150, 151, 152, 153, 154, 155, 155,
+156, 157, 158, 159, 160, 160, 161, 162, 163, 163, 164, 165, 166, 167, 167, 168,
+169, 170, 170, 171, 172, 173, 173, 174, 175, 176, 176, 177, 178, 178, 179, 180,
+181, 181, 182, 183, 183, 184, 185, 185, 186, 187, 187, 188, 189, 189, 190, 191,
+192, 192, 193, 193, 194, 195, 195, 196, 197, 197, 198, 199, 199, 200, 201, 201,
+202, 203, 203, 204, 204, 205, 206, 206, 207, 208, 208, 209, 209, 210, 211, 211,
+212, 212, 213, 214, 214, 215, 215, 216, 217, 217, 218, 218, 219, 219, 220, 221,
+221, 222, 222, 223, 224, 224, 225, 225, 226, 226, 227, 227, 228, 229, 229, 230,
+230, 231, 231, 232, 232, 233, 234, 234, 235, 235, 236, 236, 237, 237, 238, 238,
+239, 240, 240, 241, 241, 242, 242, 243, 243, 244, 244, 245, 245, 246, 246, 247,
+247, 248, 248, 249, 249, 250, 250, 251, 251, 252, 252, 253, 253, 254, 254, 255,
+];
+
+/* `ss_ilg` in its `256 <= SS_BLOCKSIZE` configuration. */
+#[inline]
+fn ss_ilg(n: isize) -> i32 {
+    let n = n as i32;
+    if n & 0xff00 != 0 {
+        8 + LG_TABLE[((n >> 8) & 0xff) as usize]
+    } else {
+        LG_TABLE[(n & 0xff) as usize]
+    }
+}
+
+#[inline]
+fn ss_isqrt(x: isize) -> isize {
+    if x >= SS_BLOCKSIZE * SS_BLOCKSIZE {
+        return SS_BLOCKSIZE;
+    }
+    let x = x as i32;
+    let e = if (x as u32) & 0xffff_0000 != 0 {
+        if (x as u32) & 0xff00_0000 != 0 {
+            24 + LG_TABLE[((x >> 24) & 0xff) as usize]
+        } else {
+            16 + LG_TABLE[((x >> 16) & 0xff) as usize]
+        }
+    } else if x & 0xff00 != 0 {
+        8 + LG_TABLE[((x >> 8) & 0xff) as usize]
+    } else {
+        LG_TABLE[(x & 0xff) as usize]
+    };
+
+    let mut y;
+    if e >= 16 {
+        y = SQQ_TABLE[(x >> ((e - 6) - (e & 1))) as usize] << ((e >> 1) - 7);
+        if e >= 24 {
+            y = (y + 1 + x / y) >> 1;
+        }
+        y = (y + 1 + x / y) >> 1;
+    } else if e >= 8 {
+        y = (SQQ_TABLE[(x >> ((e - 6) - (e & 1))) as usize] >> (7 - (e >> 1))) + 1;
+    } else {
+        return (SQQ_TABLE[x as usize] >> 4) as isize;
+    }
+
+    (if x < y * y { y - 1 } else { y }) as isize
+}
+
+/* --------------------------------------------------------------------- */
+
+/// Compares two suffixes.  `(p10, p11)` and `(p20, p21)` are the `p[0]`/`p[1]`
+/// pairs the C routine reads through its `const int*` arguments; passing the
+/// values directly also serves `sssort()`'s local two-element `PAi` array.
+#[inline]
+fn ss_compare(t: &[u8], p10: i32, p11: i32, p20: i32, p21: i32, depth: i32) -> i32 {
+    let mut u1 = (depth + p10) as isize;
+    let mut u2 = (depth + p20) as isize;
+    let u1n = (p11 + 2) as isize;
+    let u2n = (p21 + 2) as isize;
+
+    while u1 < u1n && u2 < u2n && t[u1 as usize] == t[u2 as usize] {
+        u1 += 1;
+        u2 += 1;
+    }
+
+    if u1 < u1n {
+        if u2 < u2n {
+            t[u1 as usize] as i32 - t[u2 as usize] as i32
+        } else {
+            1
+        }
+    } else if u2 < u2n {
+        -1
+    } else {
+        0
+    }
+}
+
+/// `ss_compare(T, p1, p2, depth)` for pointers `p1`/`p2` into the SA buffer.
+#[inline]
+fn ss_compare_pa(t: &[u8], sa: &[i32], p1: isize, p2: isize, depth: i32) -> i32 {
+    ss_compare(
+        t,
+        sa[p1 as usize],
+        sa[(p1 + 1) as usize],
+        sa[p2 as usize],
+        sa[(p2 + 1) as usize],
+        depth,
+    )
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Insertionsort for small size groups */
+fn ss_insertionsort(t: &[u8], sa: &mut [i32], pa: isize, first: isize, last: isize, depth: i32) {
+    let mut i = last - 2;
+    while first <= i {
+        let t0 = sa[i as usize];
+        let mut j = i + 1;
+        let mut r;
+        loop {
+            r = ss_compare_pa(t, sa, pa + t0 as isize, pa + sa[j as usize] as isize, depth);
+            if r <= 0 {
+                break;
+            }
+            loop {
+                sa[(j - 1) as usize] = sa[j as usize];
+                j += 1;
+                if !(j < last && sa[j as usize] < 0) {
+                    break;
+                }
+            }
+            if last <= j {
+                break;
+            }
+        }
+        if r == 0 {
+            sa[j as usize] = !sa[j as usize];
+        }
+        sa[(j - 1) as usize] = t0;
+        i -= 1;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/// `Td[PA[SA[p]]]` — the depth-`td` sorting key of the suffix stored at `p`.
+#[inline(always)]
+fn ss_key(t: &[u8], sa: &[i32], td: isize, pa: isize, p: isize) -> i32 {
+    t[(td + sa[(pa + sa[p as usize] as isize) as usize] as isize) as usize] as i32
+}
+
+/// `Td[v]` for an already-loaded SA element `v` (`Td[PA[v]]` in C).
+#[inline(always)]
+fn ss_key_of(t: &[u8], sa: &[i32], td: isize, pa: isize, v: i32) -> i32 {
+    t[(td + sa[(pa + v as isize) as usize] as isize) as usize] as i32
+}
+
+/// `Td[PA[SA[p]] - 1]` — the character preceding the depth-`td` key.
+#[inline(always)]
+fn ss_key_pred(t: &[u8], sa: &[i32], td: isize, pa: isize, p: isize) -> i32 {
+    t[(td + sa[(pa + sa[p as usize] as isize) as usize] as isize - 1) as usize] as i32
+}
+
+fn ss_fixdown(t: &[u8], td: isize, sa: &mut [i32], pa: isize, base: isize, i: isize, size: isize) {
+    let mut i = i;
+    let v = sa[(base + i) as usize];
+    let c = ss_key_of(t, sa, td, pa, v);
+    loop {
+        let mut j = 2 * i + 1;
+        if j >= size {
+            break;
+        }
+        let mut k = j;
+        j += 1;
+        let mut d = ss_key(t, sa, td, pa, base + k);
+        let e = ss_key(t, sa, td, pa, base + j);
+        if d < e {
+            k = j;
+            d = e;
+        }
+        if d <= c {
+            break;
+        }
+        sa[(base + i) as usize] = sa[(base + k) as usize];
+        i = k;
+    }
+    sa[(base + i) as usize] = v;
+}
+
+/* Simple top-down heapsort. */
+fn ss_heapsort(t: &[u8], td: isize, sa: &mut [i32], pa: isize, base: isize, size: isize) {
+    let mut m = size;
+    if size % 2 == 0 {
+        m -= 1;
+        if ss_key(t, sa, td, pa, base + m / 2) < ss_key(t, sa, td, pa, base + m) {
+            sa.swap((base + m) as usize, (base + m / 2) as usize);
+        }
+    }
+
+    let mut i = m / 2 - 1;
+    while 0 <= i {
+        ss_fixdown(t, td, sa, pa, base, i, m);
+        i -= 1;
+    }
+    if size % 2 == 0 {
+        sa.swap(base as usize, (base + m) as usize);
+        ss_fixdown(t, td, sa, pa, base, 0, m);
+    }
+    let mut i = m - 1;
+    while 0 < i {
+        let t0 = sa[base as usize];
+        sa[base as usize] = sa[(base + i) as usize];
+        ss_fixdown(t, td, sa, pa, base, 0, i);
+        sa[(base + i) as usize] = t0;
+        i -= 1;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Returns the median of three elements. */
+#[inline]
+fn ss_median3(
+    t: &[u8],
+    sa: &[i32],
+    td: isize,
+    pa: isize,
+    v1: isize,
+    v2: isize,
+    v3: isize,
+) -> isize {
+    let mut v1 = v1;
+    let mut v2 = v2;
+    if ss_key(t, sa, td, pa, v1) > ss_key(t, sa, td, pa, v2) {
+        std::mem::swap(&mut v1, &mut v2);
+    }
+    if ss_key(t, sa, td, pa, v2) > ss_key(t, sa, td, pa, v3) {
+        if ss_key(t, sa, td, pa, v1) > ss_key(t, sa, td, pa, v3) {
+            return v1;
+        }
+        return v3;
+    }
+    v2
+}
+
+/* Returns the median of five elements. */
+#[inline]
+fn ss_median5(
+    t: &[u8],
+    sa: &[i32],
+    td: isize,
+    pa: isize,
+    v1: isize,
+    v2: isize,
+    v3: isize,
+    v4: isize,
+    v5: isize,
+) -> isize {
+    let mut v1 = v1;
+    let mut v2 = v2;
+    let mut v3 = v3;
+    let mut v4 = v4;
+    let mut v5 = v5;
+    if ss_key(t, sa, td, pa, v2) > ss_key(t, sa, td, pa, v3) {
+        std::mem::swap(&mut v2, &mut v3);
+    }
+    if ss_key(t, sa, td, pa, v4) > ss_key(t, sa, td, pa, v5) {
+        std::mem::swap(&mut v4, &mut v5);
+    }
+    if ss_key(t, sa, td, pa, v2) > ss_key(t, sa, td, pa, v4) {
+        std::mem::swap(&mut v2, &mut v4);
+        std::mem::swap(&mut v3, &mut v5);
+    }
+    if ss_key(t, sa, td, pa, v1) > ss_key(t, sa, td, pa, v3) {
+        std::mem::swap(&mut v1, &mut v3);
+    }
+    if ss_key(t, sa, td, pa, v1) > ss_key(t, sa, td, pa, v4) {
+        std::mem::swap(&mut v1, &mut v4);
+        std::mem::swap(&mut v3, &mut v5);
+    }
+    if ss_key(t, sa, td, pa, v3) > ss_key(t, sa, td, pa, v4) {
+        return v4;
+    }
+    v3
+}
+
+/* Returns the pivot element. */
+#[inline]
+fn ss_pivot(t: &[u8], sa: &[i32], td: isize, pa: isize, first: isize, last: isize) -> isize {
+    let mut t0 = last - first;
+    let middle = first + t0 / 2;
+
+    if t0 <= 512 {
+        if t0 <= 32 {
+            return ss_median3(t, sa, td, pa, first, middle, last - 1);
+        }
+        t0 >>= 2;
+        return ss_median5(
+            t,
+            sa,
+            td,
+            pa,
+            first,
+            first + t0,
+            middle,
+            last - 1 - t0,
+            last - 1,
+        );
+    }
+    t0 >>= 3;
+    let first = ss_median3(t, sa, td, pa, first, first + t0, first + (t0 << 1));
+    let middle = ss_median3(t, sa, td, pa, middle - t0, middle, middle + t0);
+    let last = ss_median3(t, sa, td, pa, last - 1 - (t0 << 1), last - 1 - t0, last - 1);
+    ss_median3(t, sa, td, pa, first, middle, last)
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Binary partition for substrings. */
+/* The `>= x + 1` comparison deliberately mirrors the C expression shape. */
+#[allow(clippy::int_plus_one)]
+fn ss_partition(sa: &mut [i32], pa: isize, first: isize, last: isize, depth: i32) -> isize {
+    let mut a = first - 1;
+    let mut b = last;
+    loop {
+        loop {
+            a += 1;
+            if !(a < b) {
+                break;
+            }
+            if !(sa[(pa + sa[a as usize] as isize) as usize] + depth
+                >= sa[(pa + sa[a as usize] as isize + 1) as usize] + 1)
+            {
+                break;
+            }
+            sa[a as usize] = !sa[a as usize];
+        }
+        loop {
+            b -= 1;
+            if !(a < b) {
+                break;
+            }
+            if !(sa[(pa + sa[b as usize] as isize) as usize] + depth
+                < sa[(pa + sa[b as usize] as isize + 1) as usize] + 1)
+            {
+                break;
+            }
+        }
+        if b <= a {
+            break;
+        }
+        let t0 = !sa[b as usize];
+        sa[b as usize] = sa[a as usize];
+        sa[a as usize] = t0;
+    }
+    if first < a {
+        sa[first as usize] = !sa[first as usize];
+    }
+    a
+}
+
+/* Multikey introsort for medium size groups. */
+fn ss_mintrosort(t: &[u8], sa: &mut [i32], pa: isize, first: isize, last: isize, depth: i32) {
+    let mut stack = [(0isize, 0isize, 0i32, 0i32); SS_MISORT_STACKSIZE];
+    let mut ssize = 0usize;
+    let mut first = first;
+    let mut last = last;
+    let mut depth = depth;
+    let mut limit = ss_ilg(last - first);
+    let mut x: i32 = 0;
+
+    loop {
+        if last - first <= SS_INSERTIONSORT_THRESHOLD {
+            if 1 < last - first {
+                ss_insertionsort(t, sa, pa, first, last, depth);
+            }
+            /* STACK_POP */
+            if ssize == 0 {
+                return;
+            }
+            ssize -= 1;
+            (first, last, depth, limit) = stack[ssize];
+            continue;
+        }
+
+        let td = depth as isize;
+        if limit == 0 {
+            ss_heapsort(t, td, sa, pa, first, last - first);
+        }
+        limit -= 1;
+        if limit < 0 {
+            let mut a = first + 1;
+            let mut v = ss_key(t, sa, td, pa, first);
+            while a < last {
+                x = ss_key(t, sa, td, pa, a);
+                if x != v {
+                    if 1 < a - first {
+                        break;
+                    }
+                    v = x;
+                    first = a;
+                }
+                a += 1;
+            }
+            if ss_key_pred(t, sa, td, pa, first) < v {
+                first = ss_partition(sa, pa, first, a, depth);
+            }
+            if a - first <= last - a {
+                if 1 < a - first {
+                    stack[ssize] = (a, last, depth, -1);
+                    ssize += 1;
+                    last = a;
+                    depth += 1;
+                    limit = ss_ilg(a - first);
+                } else {
+                    first = a;
+                    limit = -1;
+                }
+            } else if 1 < last - a {
+                stack[ssize] = (first, a, depth + 1, ss_ilg(a - first));
+                ssize += 1;
+                first = a;
+                limit = -1;
+            } else {
+                last = a;
+                depth += 1;
+                limit = ss_ilg(a - first);
+            }
+            continue;
+        }
+
+        /* choose pivot */
+        let mut a = ss_pivot(t, sa, td, pa, first, last);
+        let v = ss_key(t, sa, td, pa, a);
+        sa.swap(first as usize, a as usize);
+
+        /* partition */
+        let mut b = first;
+        loop {
+            b += 1;
+            if !(b < last) {
+                break;
+            }
+            x = ss_key(t, sa, td, pa, b);
+            if x != v {
+                break;
+            }
+        }
+        a = b;
+        if a < last && x < v {
+            loop {
+                b += 1;
+                if !(b < last) {
+                    break;
+                }
+                x = ss_key(t, sa, td, pa, b);
+                if !(x <= v) {
+                    break;
+                }
+                if x == v {
+                    sa.swap(b as usize, a as usize);
+                    a += 1;
+                }
+            }
+        }
+        let mut c = last;
+        loop {
+            c -= 1;
+            if !(b < c) {
+                break;
+            }
+            x = ss_key(t, sa, td, pa, c);
+            if x != v {
+                break;
+            }
+        }
+        let mut d = c;
+        if b < d && x > v {
+            loop {
+                c -= 1;
+                if !(b < c) {
+                    break;
+                }
+                x = ss_key(t, sa, td, pa, c);
+                if !(x >= v) {
+                    break;
+                }
+                if x == v {
+                    sa.swap(c as usize, d as usize);
+                    d -= 1;
+                }
+            }
+        }
+        while b < c {
+            sa.swap(b as usize, c as usize);
+            loop {
+                b += 1;
+                if !(b < c) {
+                    break;
+                }
+                x = ss_key(t, sa, td, pa, b);
+                if !(x <= v) {
+                    break;
+                }
+                if x == v {
+                    sa.swap(b as usize, a as usize);
+                    a += 1;
+                }
+            }
+            loop {
+                c -= 1;
+                if !(b < c) {
+                    break;
+                }
+                x = ss_key(t, sa, td, pa, c);
+                if !(x >= v) {
+                    break;
+                }
+                if x == v {
+                    sa.swap(c as usize, d as usize);
+                    d -= 1;
+                }
+            }
+        }
+
+        if a <= d {
+            c = b - 1;
+
+            let mut s = a - first;
+            let t0 = b - a;
+            if s > t0 {
+                s = t0;
+            }
+            let mut e = first;
+            let mut f = b - s;
+            while 0 < s {
+                sa.swap(e as usize, f as usize);
+                s -= 1;
+                e += 1;
+                f += 1;
+            }
+            let mut s = d - c;
+            let t0 = last - d - 1;
+            if s > t0 {
+                s = t0;
+            }
+            let mut e = b;
+            let mut f = last - s;
+            while 0 < s {
+                sa.swap(e as usize, f as usize);
+                s -= 1;
+                e += 1;
+                f += 1;
+            }
+
+            a = first + (b - a);
+            c = last - (d - c);
+            b = if v <= ss_key_pred(t, sa, td, pa, a) {
+                a
+            } else {
+                ss_partition(sa, pa, a, c, depth)
+            };
+
+            if a - first <= last - c {
+                if last - c <= c - b {
+                    stack[ssize] = (b, c, depth + 1, ss_ilg(c - b));
+                    ssize += 1;
+                    stack[ssize] = (c, last, depth, limit);
+                    ssize += 1;
+                    last = a;
+                } else if a - first <= c - b {
+                    stack[ssize] = (c, last, depth, limit);
+                    ssize += 1;
+                    stack[ssize] = (b, c, depth + 1, ss_ilg(c - b));
+                    ssize += 1;
+                    last = a;
+                } else {
+                    stack[ssize] = (c, last, depth, limit);
+                    ssize += 1;
+                    stack[ssize] = (first, a, depth, limit);
+                    ssize += 1;
+                    first = b;
+                    last = c;
+                    depth += 1;
+                    limit = ss_ilg(c - b);
+                }
+            } else if a - first <= c - b {
+                stack[ssize] = (b, c, depth + 1, ss_ilg(c - b));
+                ssize += 1;
+                stack[ssize] = (first, a, depth, limit);
+                ssize += 1;
+                first = c;
+            } else if last - c <= c - b {
+                stack[ssize] = (first, a, depth, limit);
+                ssize += 1;
+                stack[ssize] = (b, c, depth + 1, ss_ilg(c - b));
+                ssize += 1;
+                first = c;
+            } else {
+                stack[ssize] = (first, a, depth, limit);
+                ssize += 1;
+                stack[ssize] = (c, last, depth, limit);
+                ssize += 1;
+                first = b;
+                last = c;
+                depth += 1;
+                limit = ss_ilg(c - b);
+            }
+        } else {
+            limit += 1;
+            if ss_key_pred(t, sa, td, pa, first) < v {
+                first = ss_partition(sa, pa, first, last, depth);
+                limit = ss_ilg(last - first);
+            }
+            depth += 1;
+        }
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+#[inline]
+fn ss_blockswap(sa: &mut [i32], a: isize, b: isize, n: isize) {
+    let mut a = a;
+    let mut b = b;
+    let mut n = n;
+    while 0 < n {
+        sa.swap(a as usize, b as usize);
+        n -= 1;
+        a += 1;
+        b += 1;
+    }
+}
+
+#[inline]
+fn ss_rotate(sa: &mut [i32], first: isize, middle: isize, last: isize) {
+    let mut first = first;
+    let mut last = last;
+    let mut l = middle - first;
+    let mut r = last - middle;
+    while 0 < l && 0 < r {
+        if l == r {
+            ss_blockswap(sa, first, middle, l);
+            break;
+        }
+        if l < r {
+            let mut a = last - 1;
+            let mut b = middle - 1;
+            let mut t0 = sa[a as usize];
+            loop {
+                sa[a as usize] = sa[b as usize];
+                a -= 1;
+                sa[b as usize] = sa[a as usize];
+                b -= 1;
+                if b < first {
+                    sa[a as usize] = t0;
+                    last = a;
+                    r -= l + 1;
+                    if r <= l {
+                        break;
+                    }
+                    a -= 1;
+                    b = middle - 1;
+                    t0 = sa[a as usize];
+                }
+            }
+        } else {
+            let mut a = first;
+            let mut b = middle;
+            let mut t0 = sa[a as usize];
+            loop {
+                sa[a as usize] = sa[b as usize];
+                a += 1;
+                sa[b as usize] = sa[a as usize];
+                b += 1;
+                if last <= b {
+                    sa[a as usize] = t0;
+                    first = a + 1;
+                    l -= r + 1;
+                    if l <= r {
+                        break;
+                    }
+                    a += 1;
+                    b = middle;
+                    t0 = sa[a as usize];
+                }
+            }
+        }
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+fn ss_inplacemerge(
+    t: &[u8],
+    sa: &mut [i32],
+    pa: isize,
+    first: isize,
+    middle: isize,
+    last: isize,
+    depth: i32,
+) {
+    let mut middle = middle;
+    let mut last = last;
+    loop {
+        let x: i32;
+        let p: isize;
+        if sa[(last - 1) as usize] < 0 {
+            x = 1;
+            p = pa + (!sa[(last - 1) as usize]) as isize;
+        } else {
+            x = 0;
+            p = pa + sa[(last - 1) as usize] as isize;
+        }
+        let mut a = first;
+        let mut len = middle - first;
+        let mut half = len >> 1;
+        let mut r: i32 = -1;
+        while 0 < len {
+            let b = a + half;
+            let bv = sa[b as usize];
+            let q = ss_compare_pa(
+                t,
+                sa,
+                pa + (if 0 <= bv { bv } else { !bv }) as isize,
+                p,
+                depth,
+            );
+            if q < 0 {
+                a = b + 1;
+                half -= (len & 1) ^ 1;
+            } else {
+                r = q;
+            }
+            len = half;
+            half >>= 1;
+        }
+        if a < middle {
+            if r == 0 {
+                sa[a as usize] = !sa[a as usize];
+            }
+            ss_rotate(sa, a, middle, last);
+            last -= middle - a;
+            middle = a;
+            if first == middle {
+                break;
+            }
+        }
+        last -= 1;
+        if x != 0 {
+            loop {
+                last -= 1;
+                if !(sa[last as usize] < 0) {
+                    break;
+                }
+            }
+        }
+        if middle == last {
+            break;
+        }
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Merge-forward with internal buffer. */
+fn ss_mergeforward(
+    t: &[u8],
+    sa: &mut [i32],
+    pa: isize,
+    first: isize,
+    middle: isize,
+    last: isize,
+    buf: isize,
+    depth: i32,
+) {
+    let bufend = buf + (middle - first) - 1;
+    ss_blockswap(sa, buf, first, middle - first);
+
+    let mut a = first;
+    let t0 = sa[a as usize];
+    let mut b = buf;
+    let mut c = middle;
+    loop {
+        let r = ss_compare_pa(
+            t,
+            sa,
+            pa + sa[b as usize] as isize,
+            pa + sa[c as usize] as isize,
+            depth,
+        );
+        if r < 0 {
+            loop {
+                sa[a as usize] = sa[b as usize];
+                a += 1;
+                if bufend <= b {
+                    sa[bufend as usize] = t0;
+                    return;
+                }
+                sa[b as usize] = sa[a as usize];
+                b += 1;
+                if !(sa[b as usize] < 0) {
+                    break;
+                }
+            }
+        } else if r > 0 {
+            loop {
+                sa[a as usize] = sa[c as usize];
+                a += 1;
+                sa[c as usize] = sa[a as usize];
+                c += 1;
+                if last <= c {
+                    while b < bufend {
+                        sa[a as usize] = sa[b as usize];
+                        a += 1;
+                        sa[b as usize] = sa[a as usize];
+                        b += 1;
+                    }
+                    sa[a as usize] = sa[b as usize];
+                    sa[b as usize] = t0;
+                    return;
+                }
+                if !(sa[c as usize] < 0) {
+                    break;
+                }
+            }
+        } else {
+            sa[c as usize] = !sa[c as usize];
+            loop {
+                sa[a as usize] = sa[b as usize];
+                a += 1;
+                if bufend <= b {
+                    sa[bufend as usize] = t0;
+                    return;
+                }
+                sa[b as usize] = sa[a as usize];
+                b += 1;
+                if !(sa[b as usize] < 0) {
+                    break;
+                }
+            }
+            loop {
+                sa[a as usize] = sa[c as usize];
+                a += 1;
+                sa[c as usize] = sa[a as usize];
+                c += 1;
+                if last <= c {
+                    while b < bufend {
+                        sa[a as usize] = sa[b as usize];
+                        a += 1;
+                        sa[b as usize] = sa[a as usize];
+                        b += 1;
+                    }
+                    sa[a as usize] = sa[b as usize];
+                    sa[b as usize] = t0;
+                    return;
+                }
+                if !(sa[c as usize] < 0) {
+                    break;
+                }
+            }
+        }
+    }
+}
+
+/* Merge-backward with internal buffer. */
+fn ss_mergebackward(
+    t: &[u8],
+    sa: &mut [i32],
+    pa: isize,
+    first: isize,
+    middle: isize,
+    last: isize,
+    buf: isize,
+    depth: i32,
+) {
+    let bufend = buf + (last - middle) - 1;
+    ss_blockswap(sa, buf, middle, last - middle);
+
+    let mut x = 0i32;
+    let mut p1: isize;
+    let mut p2: isize;
+    if sa[bufend as usize] < 0 {
+        p1 = pa + (!sa[bufend as usize]) as isize;
+        x |= 1;
+    } else {
+        p1 = pa + sa[bufend as usize] as isize;
+    }
+    if sa[(middle - 1) as usize] < 0 {
+        p2 = pa + (!sa[(middle - 1) as usize]) as isize;
+        x |= 2;
+    } else {
+        p2 = pa + sa[(middle - 1) as usize] as isize;
+    }
+    let mut a = last - 1;
+    let t0 = sa[a as usize];
+    let mut b = bufend;
+    let mut c = middle - 1;
+    loop {
+        let r = ss_compare_pa(t, sa, p1, p2, depth);
+        if 0 < r {
+            if x & 1 != 0 {
+                loop {
+                    sa[a as usize] = sa[b as usize];
+                    a -= 1;
+                    sa[b as usize] = sa[a as usize];
+                    b -= 1;
+                    if !(sa[b as usize] < 0) {
+                        break;
+                    }
+                }
+                x ^= 1;
+            }
+            sa[a as usize] = sa[b as usize];
+            a -= 1;
+            if b <= buf {
+                sa[buf as usize] = t0;
+                break;
+            }
+            sa[b as usize] = sa[a as usize];
+            b -= 1;
+            if sa[b as usize] < 0 {
+                p1 = pa + (!sa[b as usize]) as isize;
+                x |= 1;
+            } else {
+                p1 = pa + sa[b as usize] as isize;
+            }
+        } else if r < 0 {
+            if x & 2 != 0 {
+                loop {
+                    sa[a as usize] = sa[c as usize];
+                    a -= 1;
+                    sa[c as usize] = sa[a as usize];
+                    c -= 1;
+                    if !(sa[c as usize] < 0) {
+                        break;
+                    }
+                }
+                x ^= 2;
+            }
+            sa[a as usize] = sa[c as usize];
+            a -= 1;
+            sa[c as usize] = sa[a as usize];
+            c -= 1;
+            if c < first {
+                while buf < b {
+                    sa[a as usize] = sa[b as usize];
+                    a -= 1;
+                    sa[b as usize] = sa[a as usize];
+                    b -= 1;
+                }
+                sa[a as usize] = sa[b as usize];
+                sa[b as usize] = t0;
+                break;
+            }
+            if sa[c as usize] < 0 {
+                p2 = pa + (!sa[c as usize]) as isize;
+                x |= 2;
+            } else {
+                p2 = pa + sa[c as usize] as isize;
+            }
+        } else {
+            if x & 1 != 0 {
+                loop {
+                    sa[a as usize] = sa[b as usize];
+                    a -= 1;
+                    sa[b as usize] = sa[a as usize];
+                    b -= 1;
+                    if !(sa[b as usize] < 0) {
+                        break;
+                    }
+                }
+                x ^= 1;
+            }
+            sa[a as usize] = !sa[b as usize];
+            a -= 1;
+            if b <= buf {
+                sa[buf as usize] = t0;
+                break;
+            }
+            sa[b as usize] = sa[a as usize];
+            b -= 1;
+            if x & 2 != 0 {
+                loop {
+                    sa[a as usize] = sa[c as usize];
+                    a -= 1;
+                    sa[c as usize] = sa[a as usize];
+                    c -= 1;
+                    if !(sa[c as usize] < 0) {
+                        break;
+                    }
+                }
+                x ^= 2;
+            }
+            sa[a as usize] = sa[c as usize];
+            a -= 1;
+            sa[c as usize] = sa[a as usize];
+            c -= 1;
+            if c < first {
+                while buf < b {
+                    sa[a as usize] = sa[b as usize];
+                    a -= 1;
+                    sa[b as usize] = sa[a as usize];
+                    b -= 1;
+                }
+                sa[a as usize] = sa[b as usize];
+                sa[b as usize] = t0;
+                break;
+            }
+            if sa[b as usize] < 0 {
+                p1 = pa + (!sa[b as usize]) as isize;
+                x |= 1;
+            } else {
+                p1 = pa + sa[b as usize] as isize;
+            }
+            if sa[c as usize] < 0 {
+                p2 = pa + (!sa[c as usize]) as isize;
+                x |= 2;
+            } else {
+                p2 = pa + sa[c as usize] as isize;
+            }
+        }
+    }
+}
+
+/// `GETIDX` — undoes the "already merged" complement marking.
+#[inline(always)]
+fn getidx(a: i32) -> i32 {
+    if 0 <= a {
+        a
+    } else {
+        !a
+    }
+}
+
+/// `MERGE_CHECK` — restores or sets the complement marks after a merge.
+#[inline]
+fn ss_merge_check(t: &[u8], sa: &mut [i32], pa: isize, a: isize, b: isize, c: i32, depth: i32) {
+    if (c & 1) != 0
+        || ((c & 2) != 0
+            && ss_compare_pa(
+                t,
+                sa,
+                pa + getidx(sa[(a - 1) as usize]) as isize,
+                pa + sa[a as usize] as isize,
+                depth,
+            ) == 0)
+    {
+        sa[a as usize] = !sa[a as usize];
+    }
+    if (c & 4) != 0
+        && ss_compare_pa(
+            t,
+            sa,
+            pa + getidx(sa[(b - 1) as usize]) as isize,
+            pa + sa[b as usize] as isize,
+            depth,
+        ) == 0
+    {
+        sa[b as usize] = !sa[b as usize];
+    }
+}
+
+/* D&C based merge. */
+fn ss_swapmerge(
+    t: &[u8],
+    sa: &mut [i32],
+    pa: isize,
+    first: isize,
+    middle: isize,
+    last: isize,
+    buf: isize,
+    bufsize: isize,
+    depth: i32,
+) {
+    let mut stack = [(0isize, 0isize, 0isize, 0i32); SS_SMERGE_STACKSIZE];
+    let mut ssize = 0usize;
+    let mut first = first;
+    let mut middle = middle;
+    let mut last = last;
+    let mut check = 0i32;
+
+    loop {
+        if last - middle <= bufsize {
+            if first < middle && middle < last {
+                ss_mergebackward(t, sa, pa, first, middle, last, buf, depth);
+            }
+            ss_merge_check(t, sa, pa, first, last, check, depth);
+            if ssize == 0 {
+                return;
+            }
+            ssize -= 1;
+            (first, middle, last, check) = stack[ssize];
+            continue;
+        }
+
+        if middle - first <= bufsize {
+            if first < middle {
+                ss_mergeforward(t, sa, pa, first, middle, last, buf, depth);
+            }
+            ss_merge_check(t, sa, pa, first, last, check, depth);
+            if ssize == 0 {
+                return;
+            }
+            ssize -= 1;
+            (first, middle, last, check) = stack[ssize];
+            continue;
+        }
+
+        let mut m: isize = 0;
+        let mut len = std::cmp::min(middle - first, last - middle);
+        let mut half = len >> 1;
+        while 0 < len {
+            if ss_compare_pa(
+                t,
+                sa,
+                pa + getidx(sa[(middle + m + half) as usize]) as isize,
+                pa + getidx(sa[(middle - m - half - 1) as usize]) as isize,
+                depth,
+            ) < 0
+            {
+                m += half + 1;
+                half -= (len & 1) ^ 1;
+            }
+            len = half;
+            half >>= 1;
+        }
+
+        if 0 < m {
+            let lm = middle - m;
+            let rm = middle + m;
+            ss_blockswap(sa, lm, middle, m);
+            let mut l = middle;
+            let mut r = middle;
+            let mut next = 0i32;
+            if rm < last {
+                if sa[rm as usize] < 0 {
+                    sa[rm as usize] = !sa[rm as usize];
+                    if first < lm {
+                        loop {
+                            l -= 1;
+                            if !(sa[l as usize] < 0) {
+                                break;
+                            }
+                        }
+                        next |= 4;
+                    }
+                    next |= 1;
+                } else if first < lm {
+                    while sa[r as usize] < 0 {
+                        r += 1;
+                    }
+                    next |= 2;
+                }
+            }
+
+            if l - first <= last - r {
+                stack[ssize] = (r, rm, last, (next & 3) | (check & 4));
+                ssize += 1;
+                middle = lm;
+                last = l;
+                check = (check & 3) | (next & 4);
+            } else {
+                if (next & 2) != 0 && r == middle {
+                    next ^= 6;
+                }
+                stack[ssize] = (first, lm, l, (check & 3) | (next & 4));
+                ssize += 1;
+                first = r;
+                middle = rm;
+                check = (next & 3) | (check & 4);
+            }
+        } else {
+            if ss_compare_pa(
+                t,
+                sa,
+                pa + getidx(sa[(middle - 1) as usize]) as isize,
+                pa + sa[middle as usize] as isize,
+                depth,
+            ) == 0
+            {
+                sa[middle as usize] = !sa[middle as usize];
+            }
+            ss_merge_check(t, sa, pa, first, last, check, depth);
+            if ssize == 0 {
+                return;
+            }
+            ssize -= 1;
+            (first, middle, last, check) = stack[ssize];
+        }
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Substring sort */
+fn sssort(
+    t: &[u8],
+    sa: &mut [i32],
+    pa: isize,
+    first: isize,
+    last: isize,
+    buf: isize,
+    bufsize: isize,
+    depth: i32,
+    n: isize,
+    lastsuffix: bool,
+) {
+    let mut first = first;
+    let mut buf = buf;
+    let mut bufsize = bufsize;
+
+    if lastsuffix {
+        first += 1;
+    }
+
+    let mut limit: isize = 0;
+    let mut middle = last;
+    if bufsize < SS_BLOCKSIZE && bufsize < last - first {
+        limit = ss_isqrt(last - first);
+        if bufsize < limit {
+            if SS_BLOCKSIZE < limit {
+                limit = SS_BLOCKSIZE;
+            }
+            middle = last - limit;
+            buf = middle;
+            bufsize = limit;
+        } else {
+            limit = 0;
+        }
+    }
+    let mut a = first;
+    let mut i: isize = 0;
+    while SS_BLOCKSIZE < middle - a {
+        ss_mintrosort(t, sa, pa, a, a + SS_BLOCKSIZE, depth);
+        let mut curbufsize = last - (a + SS_BLOCKSIZE);
+        let mut curbuf = a + SS_BLOCKSIZE;
+        if curbufsize <= bufsize {
+            curbufsize = bufsize;
+            curbuf = buf;
+        }
+        let mut b = a;
+        let mut k = SS_BLOCKSIZE;
+        let mut j = i;
+        while j & 1 != 0 {
+            ss_swapmerge(t, sa, pa, b - k, b, b + k, curbuf, curbufsize, depth);
+            b -= k;
+            k <<= 1;
+            j >>= 1;
+        }
+        a += SS_BLOCKSIZE;
+        i += 1;
+    }
+    ss_mintrosort(t, sa, pa, a, middle, depth);
+    let mut k = SS_BLOCKSIZE;
+    while i != 0 {
+        if i & 1 != 0 {
+            ss_swapmerge(t, sa, pa, a - k, a, middle, buf, bufsize, depth);
+            a -= k;
+        }
+        k <<= 1;
+        i >>= 1;
+    }
+    if limit != 0 {
+        ss_mintrosort(t, sa, pa, middle, last, depth);
+        ss_inplacemerge(t, sa, pa, first, middle, last, depth);
+    }
+
+    if lastsuffix {
+        /* Insert last type B* suffix. */
+        let pai0 = sa[(pa + sa[(first - 1) as usize] as isize) as usize];
+        let pai1 = (n - 2) as i32;
+        let i0 = sa[(first - 1) as usize];
+        let mut a = first;
+        while a < last {
+            let av = sa[a as usize];
+            if !(av < 0
+                || 0 < ss_compare(
+                    t,
+                    pai0,
+                    pai1,
+                    sa[(pa + av as isize) as usize],
+                    sa[(pa + av as isize + 1) as usize],
+                    depth,
+                ))
+            {
+                break;
+            }
+            sa[(a - 1) as usize] = av;
+            a += 1;
+        }
+        sa[(a - 1) as usize] = i0;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+#[inline]
+fn tr_ilg(n: isize) -> i32 {
+    let n = n as i32;
+    if (n as u32) & 0xffff_0000 != 0 {
+        if (n as u32) & 0xff00_0000 != 0 {
+            24 + LG_TABLE[((n >> 24) & 0xff) as usize]
+        } else {
+            16 + LG_TABLE[((n >> 16) & 0xff) as usize]
+        }
+    } else if n & 0xff00 != 0 {
+        8 + LG_TABLE[((n >> 8) & 0xff) as usize]
+    } else {
+        LG_TABLE[(n & 0xff) as usize]
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/// `ISAd[SA[p]]` — the depth-offset rank of the suffix stored at `p`.
+#[inline(always)]
+fn tr_key(sa: &[i32], isad: isize, p: isize) -> i32 {
+    sa[(isad + sa[p as usize] as isize) as usize]
+}
+
+/* Simple insertionsort for small size groups. */
+fn tr_insertionsort(sa: &mut [i32], isad: isize, first: isize, last: isize) {
+    let mut a = first + 1;
+    while a < last {
+        let t0 = sa[a as usize];
+        let mut b = a - 1;
+        let mut r;
+        loop {
+            r = sa[(isad + t0 as isize) as usize] - tr_key(sa, isad, b);
+            if !(0 > r) {
+                break;
+            }
+            loop {
+                sa[(b + 1) as usize] = sa[b as usize];
+                b -= 1;
+                if !(first <= b && sa[b as usize] < 0) {
+                    break;
+                }
+            }
+            if b < first {
+                break;
+            }
+        }
+        if r == 0 {
+            sa[b as usize] = !sa[b as usize];
+        }
+        sa[(b + 1) as usize] = t0;
+        a += 1;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+fn tr_fixdown(sa: &mut [i32], isad: isize, base: isize, i: isize, size: isize) {
+    let mut i = i;
+    let v = sa[(base + i) as usize];
+    let c = sa[(isad + v as isize) as usize];
+    loop {
+        let mut j = 2 * i + 1;
+        if j >= size {
+            break;
+        }
+        let mut k = j;
+        j += 1;
+        let mut d = tr_key(sa, isad, base + k);
+        let e = tr_key(sa, isad, base + j);
+        if d < e {
+            k = j;
+            d = e;
+        }
+        if d <= c {
+            break;
+        }
+        sa[(base + i) as usize] = sa[(base + k) as usize];
+        i = k;
+    }
+    sa[(base + i) as usize] = v;
+}
+
+/* Simple top-down heapsort. */
+fn tr_heapsort(sa: &mut [i32], isad: isize, base: isize, size: isize) {
+    let mut m = size;
+    if size % 2 == 0 {
+        m -= 1;
+        if tr_key(sa, isad, base + m / 2) < tr_key(sa, isad, base + m) {
+            sa.swap((base + m) as usize, (base + m / 2) as usize);
+        }
+    }
+
+    let mut i = m / 2 - 1;
+    while 0 <= i {
+        tr_fixdown(sa, isad, base, i, m);
+        i -= 1;
+    }
+    if size % 2 == 0 {
+        sa.swap(base as usize, (base + m) as usize);
+        tr_fixdown(sa, isad, base, 0, m);
+    }
+    let mut i = m - 1;
+    while 0 < i {
+        let t0 = sa[base as usize];
+        sa[base as usize] = sa[(base + i) as usize];
+        tr_fixdown(sa, isad, base, 0, i);
+        sa[(base + i) as usize] = t0;
+        i -= 1;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Returns the median of three elements. */
+#[inline]
+fn tr_median3(sa: &[i32], isad: isize, v1: isize, v2: isize, v3: isize) -> isize {
+    let mut v1 = v1;
+    let mut v2 = v2;
+    if tr_key(sa, isad, v1) > tr_key(sa, isad, v2) {
+        std::mem::swap(&mut v1, &mut v2);
+    }
+    if tr_key(sa, isad, v2) > tr_key(sa, isad, v3) {
+        if tr_key(sa, isad, v1) > tr_key(sa, isad, v3) {
+            return v1;
+        }
+        return v3;
+    }
+    v2
+}
+
+/* Returns the median of five elements. */
+#[inline]
+fn tr_median5(
+    sa: &[i32],
+    isad: isize,
+    v1: isize,
+    v2: isize,
+    v3: isize,
+    v4: isize,
+    v5: isize,
+) -> isize {
+    let mut v1 = v1;
+    let mut v2 = v2;
+    let mut v3 = v3;
+    let mut v4 = v4;
+    let mut v5 = v5;
+    if tr_key(sa, isad, v2) > tr_key(sa, isad, v3) {
+        std::mem::swap(&mut v2, &mut v3);
+    }
+    if tr_key(sa, isad, v4) > tr_key(sa, isad, v5) {
+        std::mem::swap(&mut v4, &mut v5);
+    }
+    if tr_key(sa, isad, v2) > tr_key(sa, isad, v4) {
+        std::mem::swap(&mut v2, &mut v4);
+        std::mem::swap(&mut v3, &mut v5);
+    }
+    if tr_key(sa, isad, v1) > tr_key(sa, isad, v3) {
+        std::mem::swap(&mut v1, &mut v3);
+    }
+    if tr_key(sa, isad, v1) > tr_key(sa, isad, v4) {
+        std::mem::swap(&mut v1, &mut v4);
+        std::mem::swap(&mut v3, &mut v5);
+    }
+    if tr_key(sa, isad, v3) > tr_key(sa, isad, v4) {
+        return v4;
+    }
+    v3
+}
+
+/* Returns the pivot element. */
+#[inline]
+fn tr_pivot(sa: &[i32], isad: isize, first: isize, last: isize) -> isize {
+    let mut t0 = last - first;
+    let middle = first + t0 / 2;
+
+    if t0 <= 512 {
+        if t0 <= 32 {
+            return tr_median3(sa, isad, first, middle, last - 1);
+        }
+        t0 >>= 2;
+        return tr_median5(sa, isad, first, first + t0, middle, last - 1 - t0, last - 1);
+    }
+    t0 >>= 3;
+    let first = tr_median3(sa, isad, first, first + t0, first + (t0 << 1));
+    let middle = tr_median3(sa, isad, middle - t0, middle, middle + t0);
+    let last = tr_median3(sa, isad, last - 1 - (t0 << 1), last - 1 - t0, last - 1);
+    tr_median3(sa, isad, first, middle, last)
+}
+
+/* --------------------------------------------------------------------- */
+
+struct TrBudget {
+    chance: i32,
+    remain: i32,
+    incval: i32,
+    count: i32,
+}
+
+impl TrBudget {
+    fn new(chance: i32, incval: i32) -> Self {
+        TrBudget {
+            chance,
+            remain: incval,
+            incval,
+            count: 0,
+        }
+    }
+
+    fn check(&mut self, size: isize) -> bool {
+        let size = size as i32;
+        if size <= self.remain {
+            self.remain -= size;
+            return true;
+        }
+        if self.chance == 0 {
+            self.count += size;
+            return false;
+        }
+        self.remain += self.incval - size;
+        self.chance -= 1;
+        true
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+fn tr_partition(
+    sa: &mut [i32],
+    isad: isize,
+    first: isize,
+    middle: isize,
+    last: isize,
+    v: i32,
+) -> (isize, isize) {
+    let mut first = first;
+    let mut last = last;
+    let mut x: i32 = 0;
+
+    let mut b = middle - 1;
+    loop {
+        b += 1;
+        if !(b < last) {
+            break;
+        }
+        x = tr_key(sa, isad, b);
+        if x != v {
+            break;
+        }
+    }
+    let mut a = b;
+    if a < last && x < v {
+        loop {
+            b += 1;
+            if !(b < last) {
+                break;
+            }
+            x = tr_key(sa, isad, b);
+            if !(x <= v) {
+                break;
+            }
+            if x == v {
+                sa.swap(b as usize, a as usize);
+                a += 1;
+            }
+        }
+    }
+    let mut c = last;
+    loop {
+        c -= 1;
+        if !(b < c) {
+            break;
+        }
+        x = tr_key(sa, isad, c);
+        if x != v {
+            break;
+        }
+    }
+    let mut d = c;
+    if b < d && x > v {
+        loop {
+            c -= 1;
+            if !(b < c) {
+                break;
+            }
+            x = tr_key(sa, isad, c);
+            if !(x >= v) {
+                break;
+            }
+            if x == v {
+                sa.swap(c as usize, d as usize);
+                d -= 1;
+            }
+        }
+    }
+    while b < c {
+        sa.swap(b as usize, c as usize);
+        loop {
+            b += 1;
+            if !(b < c) {
+                break;
+            }
+            x = tr_key(sa, isad, b);
+            if !(x <= v) {
+                break;
+            }
+            if x == v {
+                sa.swap(b as usize, a as usize);
+                a += 1;
+            }
+        }
+        loop {
+            c -= 1;
+            if !(b < c) {
+                break;
+            }
+            x = tr_key(sa, isad, c);
+            if !(x >= v) {
+                break;
+            }
+            if x == v {
+                sa.swap(c as usize, d as usize);
+                d -= 1;
+            }
+        }
+    }
+
+    if a <= d {
+        c = b - 1;
+        let mut s = a - first;
+        let t0 = b - a;
+        if s > t0 {
+            s = t0;
+        }
+        let mut e = first;
+        let mut f = b - s;
+        while 0 < s {
+            sa.swap(e as usize, f as usize);
+            s -= 1;
+            e += 1;
+            f += 1;
+        }
+        let mut s = d - c;
+        let t0 = last - d - 1;
+        if s > t0 {
+            s = t0;
+        }
+        let mut e = b;
+        let mut f = last - s;
+        while 0 < s {
+            sa.swap(e as usize, f as usize);
+            s -= 1;
+            e += 1;
+            f += 1;
+        }
+        first += b - a;
+        last -= d - c;
+    }
+    (first, last)
+}
+
+/* sort suffixes of middle partition by using sorted order of suffixes of
+ * left and right partition. */
+fn tr_copy(
+    sa: &mut [i32],
+    isa: isize,
+    first: isize,
+    a: isize,
+    b: isize,
+    last: isize,
+    depth: isize,
+) {
+    /* All cursor arithmetic is relative to the slice start, which is the C
+     * routine's `SA` pointer, so `x - SA` becomes plain `x`. */
+    let v = (b - 1) as i32;
+
+    let mut c = first;
+    let mut d = a - 1;
+    while c <= d {
+        let s = sa[c as usize] - depth as i32;
+        if 0 <= s && sa[(isa + s as isize) as usize] == v {
+            d += 1;
+            sa[d as usize] = s;
+            sa[(isa + s as isize) as usize] = d as i32;
+        }
+        c += 1;
+    }
+    let mut c = last - 1;
+    let e = d + 1;
+    let mut d = b;
+    while e < d {
+        let s = sa[c as usize] - depth as i32;
+        if 0 <= s && sa[(isa + s as isize) as usize] == v {
+            d -= 1;
+            sa[d as usize] = s;
+            sa[(isa + s as isize) as usize] = d as i32;
+        }
+        c -= 1;
+    }
+}
+
+fn tr_partialcopy(
+    sa: &mut [i32],
+    isa: isize,
+    first: isize,
+    a: isize,
+    b: isize,
+    last: isize,
+    depth: isize,
+) {
+    let v = (b - 1) as i32;
+    let mut newrank: i32 = -1;
+
+    let mut lastrank: i32 = -1;
+    let mut c = first;
+    let mut d = a - 1;
+    while c <= d {
+        let s = sa[c as usize] - depth as i32;
+        if 0 <= s && sa[(isa + s as isize) as usize] == v {
+            d += 1;
+            sa[d as usize] = s;
+            let rank = sa[(isa + s as isize + depth) as usize];
+            if lastrank != rank {
+                lastrank = rank;
+                newrank = d as i32;
+            }
+            sa[(isa + s as isize) as usize] = newrank;
+        }
+        c += 1;
+    }
+
+    let mut lastrank: i32 = -1;
+    let mut e = d;
+    while first <= e {
+        let rank = sa[(isa + sa[e as usize] as isize) as usize];
+        if lastrank != rank {
+            lastrank = rank;
+            newrank = e as i32;
+        }
+        if newrank != rank {
+            sa[(isa + sa[e as usize] as isize) as usize] = newrank;
+        }
+        e -= 1;
+    }
+
+    let mut lastrank: i32 = -1;
+    let mut c = last - 1;
+    let e = d + 1;
+    let mut d = b;
+    while e < d {
+        let s = sa[c as usize] - depth as i32;
+        if 0 <= s && sa[(isa + s as isize) as usize] == v {
+            d -= 1;
+            sa[d as usize] = s;
+            let rank = sa[(isa + s as isize + depth) as usize];
+            if lastrank != rank {
+                lastrank = rank;
+                newrank = d as i32;
+            }
+            sa[(isa + s as isize) as usize] = newrank;
+        }
+        c -= 1;
+    }
+}
+
+fn tr_introsort(
+    sa: &mut [i32],
+    isa: isize,
+    isad: isize,
+    first: isize,
+    last: isize,
+    budget: &mut TrBudget,
+) {
+    /* Stack frames are (ISAd, first, last, limit, trlink); the tandem-repeat
+     * copy frame stores its `(a, b)` pair in the pointer fields with a zero
+     * placeholder where C pushes a NULL ISAd. */
+    let mut stack = [(0isize, 0isize, 0isize, 0i32, 0i32); TR_STACKSIZE];
+    let mut ssize = 0usize;
+    let mut trlink: i32 = -1;
+    let mut isad = isad;
+    let mut first = first;
+    let mut last = last;
+    let incr = isad - isa;
+    let mut limit = tr_ilg(last - first);
+
+    loop {
+        if limit < 0 {
+            if limit == -1 {
+                /* tandem repeat partition */
+                let (a, b) = tr_partition(sa, isad - incr, first, first, last, (last - 1) as i32);
+
+                /* update ranks */
+                if a < last {
+                    let v = (a - 1) as i32;
+                    let mut c = first;
+                    while c < a {
+                        sa[(isa + sa[c as usize] as isize) as usize] = v;
+                        c += 1;
+                    }
+                }
+                if b < last {
+                    let v = (b - 1) as i32;
+                    let mut c = a;
+                    while c < b {
+                        sa[(isa + sa[c as usize] as isize) as usize] = v;
+                        c += 1;
+                    }
+                }
+
+                /* push */
+                if 1 < b - a {
+                    stack[ssize] = (0, a, b, 0, 0);
+                    ssize += 1;
+                    stack[ssize] = (isad - incr, first, last, -2, trlink);
+                    ssize += 1;
+                    trlink = ssize as i32 - 2;
+                }
+                if a - first <= last - b {
+                    if 1 < a - first {
+                        stack[ssize] = (isad, b, last, tr_ilg(last - b), trlink);
+                        ssize += 1;
+                        last = a;
+                        limit = tr_ilg(a - first);
+                    } else if 1 < last - b {
+                        first = b;
+                        limit = tr_ilg(last - b);
+                    } else {
+                        if ssize == 0 {
+                            return;
+                        }
+                        ssize -= 1;
+                        (isad, first, last, limit, trlink) = stack[ssize];
+                    }
+                } else if 1 < last - b {
+                    stack[ssize] = (isad, first, a, tr_ilg(a - first), trlink);
+                    ssize += 1;
+                    first = b;
+                    limit = tr_ilg(last - b);
+                } else if 1 < a - first {
+                    last = a;
+                    limit = tr_ilg(a - first);
+                } else {
+                    if ssize == 0 {
+                        return;
+                    }
+                    ssize -= 1;
+                    (isad, first, last, limit, trlink) = stack[ssize];
+                }
+            } else if limit == -2 {
+                /* tandem repeat copy */
+                ssize -= 1;
+                let a = stack[ssize].1;
+                let b = stack[ssize].2;
+                if stack[ssize].3 == 0 {
+                    tr_copy(sa, isa, first, a, b, last, isad - isa);
+                } else {
+                    if 0 <= trlink {
+                        stack[trlink as usize].3 = -1;
+                    }
+                    tr_partialcopy(sa, isa, first, a, b, last, isad - isa);
+                }
+                if ssize == 0 {
+                    return;
+                }
+                ssize -= 1;
+                (isad, first, last, limit, trlink) = stack[ssize];
+            } else {
+                /* sorted partition */
+                if 0 <= sa[first as usize] {
+                    let mut a = first;
+                    loop {
+                        sa[(isa + sa[a as usize] as isize) as usize] = a as i32;
+                        a += 1;
+                        if !(a < last && 0 <= sa[a as usize]) {
+                            break;
+                        }
+                    }
+                    first = a;
+                }
+                if first < last {
+                    let mut a = first;
+                    loop {
+                        sa[a as usize] = !sa[a as usize];
+                        a += 1;
+                        if !(sa[a as usize] < 0) {
+                            break;
+                        }
+                    }
+                    let next =
+                        if sa[(isa + sa[a as usize] as isize) as usize] != tr_key(sa, isad, a) {
+                            tr_ilg(a - first + 1)
+                        } else {
+                            -1
+                        };
+                    a += 1;
+                    if a < last {
+                        let v = (a - 1) as i32;
+                        let mut b = first;
+                        while b < a {
+                            sa[(isa + sa[b as usize] as isize) as usize] = v;
+                            b += 1;
+                        }
+                    }
+
+                    /* push */
+                    if budget.check(a - first) {
+                        if a - first <= last - a {
+                            stack[ssize] = (isad, a, last, -3, trlink);
+                            ssize += 1;
+                            isad += incr;
+                            last = a;
+                            limit = next;
+                        } else if 1 < last - a {
+                            stack[ssize] = (isad + incr, first, a, next, trlink);
+                            ssize += 1;
+                            first = a;
+                            limit = -3;
+                        } else {
+                            isad += incr;
+                            last = a;
+                            limit = next;
+                        }
+                    } else {
+                        if 0 <= trlink {
+                            stack[trlink as usize].3 = -1;
+                        }
+                        if 1 < last - a {
+                            first = a;
+                            limit = -3;
+                        } else {
+                            if ssize == 0 {
+                                return;
+                            }
+                            ssize -= 1;
+                            (isad, first, last, limit, trlink) = stack[ssize];
+                        }
+                    }
+                } else {
+                    if ssize == 0 {
+                        return;
+                    }
+                    ssize -= 1;
+                    (isad, first, last, limit, trlink) = stack[ssize];
+                }
+            }
+            continue;
+        }
+
+        if last - first <= TR_INSERTIONSORT_THRESHOLD {
+            tr_insertionsort(sa, isad, first, last);
+            limit = -3;
+            continue;
+        }
+
+        /* C decrements `limit` here (`limit-- == 0`); the decrement is
+         * observable only on the not-taken path because the taken path
+         * overwrites `limit` with -3. */
+        if limit == 0 {
+            tr_heapsort(sa, isad, first, last - first);
+            let mut a = last - 1;
+            while first < a {
+                let x = tr_key(sa, isad, a);
+                let mut b = a - 1;
+                while first <= b && tr_key(sa, isad, b) == x {
+                    sa[b as usize] = !sa[b as usize];
+                    b -= 1;
+                }
+                a = b;
+            }
+            limit = -3;
+            continue;
+        }
+        limit -= 1;
+
+        /* choose pivot */
+        let a = tr_pivot(sa, isad, first, last);
+        sa.swap(first as usize, a as usize);
+        let v = tr_key(sa, isad, first);
+
+        /* partition */
+        let (a, b) = tr_partition(sa, isad, first, first + 1, last, v);
+        if last - first != b - a {
+            let next = if sa[(isa + sa[a as usize] as isize) as usize] != v {
+                tr_ilg(b - a)
+            } else {
+                -1
+            };
+
+            /* update ranks */
+            {
+                let vv = (a - 1) as i32;
+                let mut c = first;
+                while c < a {
+                    sa[(isa + sa[c as usize] as isize) as usize] = vv;
+                    c += 1;
+                }
+            }
+            if b < last {
+                let vv = (b - 1) as i32;
+                let mut c = a;
+                while c < b {
+                    sa[(isa + sa[c as usize] as isize) as usize] = vv;
+                    c += 1;
+                }
+            }
+
+            /* push */
+            if 1 < b - a && budget.check(b - a) {
+                if a - first <= last - b {
+                    if last - b <= b - a {
+                        if 1 < a - first {
+                            stack[ssize] = (isad + incr, a, b, next, trlink);
+                            ssize += 1;
+                            stack[ssize] = (isad, b, last, limit, trlink);
+                            ssize += 1;
+                            last = a;
+                        } else if 1 < last - b {
+                            stack[ssize] = (isad + incr, a, b, next, trlink);
+                            ssize += 1;
+                            first = b;
+                        } else {
+                            isad += incr;
+                            first = a;
+                            last = b;
+                            limit = next;
+                        }
+                    } else if a - first <= b - a {
+                        if 1 < a - first {
+                            stack[ssize] = (isad, b, last, limit, trlink);
+                            ssize += 1;
+                            stack[ssize] = (isad + incr, a, b, next, trlink);
+                            ssize += 1;
+                            last = a;
+                        } else {
+                            stack[ssize] = (isad, b, last, limit, trlink);
+                            ssize += 1;
+                            isad += incr;
+                            first = a;
+                            last = b;
+                            limit = next;
+                        }
+                    } else {
+                        stack[ssize] = (isad, b, last, limit, trlink);
+                        ssize += 1;
+                        stack[ssize] = (isad, first, a, limit, trlink);
+                        ssize += 1;
+                        isad += incr;
+                        first = a;
+                        last = b;
+                        limit = next;
+                    }
+                } else if a - first <= b - a {
+                    if 1 < last - b {
+                        stack[ssize] = (isad + incr, a, b, next, trlink);
+                        ssize += 1;
+                        stack[ssize] = (isad, first, a, limit, trlink);
+                        ssize += 1;
+                        first = b;
+                    } else if 1 < a - first {
+                        stack[ssize] = (isad + incr, a, b, next, trlink);
+                        ssize += 1;
+                        last = a;
+                    } else {
+                        isad += incr;
+                        first = a;
+                        last = b;
+                        limit = next;
+                    }
+                } else if last - b <= b - a {
+                    if 1 < last - b {
+                        stack[ssize] = (isad, first, a, limit, trlink);
+                        ssize += 1;
+                        stack[ssize] = (isad + incr, a, b, next, trlink);
+                        ssize += 1;
+                        first = b;
+                    } else {
+                        stack[ssize] = (isad, first, a, limit, trlink);
+                        ssize += 1;
+                        isad += incr;
+                        first = a;
+                        last = b;
+                        limit = next;
+                    }
+                } else {
+                    stack[ssize] = (isad, first, a, limit, trlink);
+                    ssize += 1;
+                    stack[ssize] = (isad, b, last, limit, trlink);
+                    ssize += 1;
+                    isad += incr;
+                    first = a;
+                    last = b;
+                    limit = next;
+                }
+            } else {
+                if 1 < b - a && 0 <= trlink {
+                    stack[trlink as usize].3 = -1;
+                }
+                if a - first <= last - b {
+                    if 1 < a - first {
+                        stack[ssize] = (isad, b, last, limit, trlink);
+                        ssize += 1;
+                        last = a;
+                    } else if 1 < last - b {
+                        first = b;
+                    } else {
+                        if ssize == 0 {
+                            return;
+                        }
+                        ssize -= 1;
+                        (isad, first, last, limit, trlink) = stack[ssize];
+                    }
+                } else if 1 < last - b {
+                    stack[ssize] = (isad, first, a, limit, trlink);
+                    ssize += 1;
+                    first = b;
+                } else if 1 < a - first {
+                    last = a;
+                } else {
+                    if ssize == 0 {
+                        return;
+                    }
+                    ssize -= 1;
+                    (isad, first, last, limit, trlink) = stack[ssize];
+                }
+            }
+        } else if budget.check(last - first) {
+            limit = tr_ilg(last - first);
+            isad += incr;
+        } else {
+            if 0 <= trlink {
+                stack[trlink as usize].3 = -1;
+            }
+            if ssize == 0 {
+                return;
+            }
+            ssize -= 1;
+            (isad, first, last, limit, trlink) = stack[ssize];
+        }
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/* Tandem repeat sort */
+fn trsort(sa: &mut [i32], isa: isize, n: isize, depth: isize) {
+    let mut budget = TrBudget::new(tr_ilg(n) * 2 / 3, n as i32);
+    /* trbudget_init(&budget, tr_ilg(n) * 3 / 4, n); */
+    let mut isad = isa + depth;
+    while -(n as i32) < sa[0] {
+        let mut first: isize = 0;
+        let mut skip: isize = 0;
+        let mut unsorted: i32 = 0;
+        loop {
+            let t0 = sa[first as usize];
+            if t0 < 0 {
+                first -= t0 as isize;
+                skip += t0 as isize;
+            } else {
+                if skip != 0 {
+                    sa[(first + skip) as usize] = skip as i32;
+                    skip = 0;
+                }
+                let last = sa[(isa + t0 as isize) as usize] as isize + 1;
+                if 1 < last - first {
+                    budget.count = 0;
+                    tr_introsort(sa, isa, isad, first, last, &mut budget);
+                    if budget.count != 0 {
+                        unsorted += budget.count;
+                    } else {
+                        skip = first - last;
+                    }
+                } else if last - first == 1 {
+                    skip = -1;
+                }
+                first = last;
+            }
+            if !(first < n) {
+                break;
+            }
+        }
+        if skip != 0 {
+            sa[(first + skip) as usize] = skip as i32;
+        }
+        if unsorted == 0 {
+            break;
+        }
+        isad += isad - isa;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/// `BUCKET_B(c0, c1)` for the 256-symbol alphabet.
+#[inline(always)]
+fn bb(c0: i32, c1: i32) -> usize {
+    (((c1 as u32) << 8) | c0 as u32) as usize
+}
+
+/// `BUCKET_BSTAR(c0, c1)` for the 256-symbol alphabet.
+#[inline(always)]
+fn bstar(c0: i32, c1: i32) -> usize {
+    (((c0 as u32) << 8) | c1 as u32) as usize
+}
+
+/* Sorts suffixes of type B*. */
+fn sort_type_bstar(
+    t: &[u8],
+    sa: &mut [i32],
+    bucket_a: &mut [i32],
+    bucket_b: &mut [i32],
+    n: isize,
+) -> isize {
+    /* Initialize bucket arrays. */
+    for slot in bucket_a.iter_mut() {
+        *slot = 0;
+    }
+    for slot in bucket_b.iter_mut() {
+        *slot = 0;
+    }
+
+    /* Count the number of occurrences of the first one or two characters of
+    each type A, B and B* suffix. Moreover, store the beginning position of
+    all type B* suffixes into the array SA. */
+    let mut i = n - 1;
+    let mut m = n;
+    let mut c0 = t[(n - 1) as usize] as i32;
+    let mut c1;
+    while 0 <= i {
+        /* type A suffix. */
+        loop {
+            c1 = c0;
+            bucket_a[c1 as usize] += 1;
+            i -= 1;
+            if 0 <= i {
+                c0 = t[i as usize] as i32;
+                if c0 >= c1 {
+                    continue;
+                }
+            }
+            break;
+        }
+        if 0 <= i {
+            /* type B* suffix. */
+            bucket_b[bstar(c0, c1)] += 1;
+            m -= 1;
+            sa[m as usize] = i as i32;
+            /* type B suffix. */
+            i -= 1;
+            c1 = c0;
+            while 0 <= i {
+                c0 = t[i as usize] as i32;
+                if !(c0 <= c1) {
+                    break;
+                }
+                bucket_b[bb(c0, c1)] += 1;
+                i -= 1;
+                c1 = c0;
+            }
+        }
+    }
+    let m = n - m;
+    /*
+    note:
+      A type B* suffix is lexicographically smaller than a type B suffix that
+      begins with the same first two characters.
+    */
+
+    /* Calculate the index of start/end point of each bucket. */
+    {
+        let mut i: i32 = 0;
+        let mut j: i32 = 0;
+        for c0 in 0..ALPHABET_SIZE {
+            let t0 = i + bucket_a[c0 as usize];
+            bucket_a[c0 as usize] = i + j; /* start point */
+            i = t0 + bucket_b[bb(c0, c0)];
+            for c1 in (c0 + 1)..ALPHABET_SIZE {
+                j += bucket_b[bstar(c0, c1)];
+                bucket_b[bstar(c0, c1)] = j; /* end point */
+                i += bucket_b[bb(c0, c1)];
+            }
+        }
+    }
+
+    if 0 < m {
+        /* Sort the type B* suffixes by their first two characters. */
+        let pab = n - m;
+        let isab = m;
+        let mut i = m - 2;
+        while 0 <= i {
+            let t0 = sa[(pab + i) as usize];
+            let c0 = t[t0 as usize] as i32;
+            let c1 = t[(t0 + 1) as usize] as i32;
+            bucket_b[bstar(c0, c1)] -= 1;
+            sa[bucket_b[bstar(c0, c1)] as usize] = i as i32;
+            i -= 1;
+        }
+        {
+            let t0 = sa[(pab + m - 1) as usize];
+            let c0 = t[t0 as usize] as i32;
+            let c1 = t[(t0 + 1) as usize] as i32;
+            bucket_b[bstar(c0, c1)] -= 1;
+            sa[bucket_b[bstar(c0, c1)] as usize] = (m - 1) as i32;
+        }
+
+        /* Sort the type B* substrings using sssort. */
+        let buf = m;
+        let bufsize = n - 2 * m;
+        let mut c0 = ALPHABET_SIZE - 2;
+        let mut j = m;
+        while 0 < j {
+            let mut c1 = ALPHABET_SIZE - 1;
+            while c0 < c1 {
+                let i = bucket_b[bstar(c0, c1)] as isize;
+                if 1 < j - i {
+                    sssort(
+                        t,
+                        sa,
+                        pab,
+                        i,
+                        j,
+                        buf,
+                        bufsize,
+                        2,
+                        n,
+                        sa[i as usize] == (m - 1) as i32,
+                    );
+                }
+                j = i;
+                c1 -= 1;
+            }
+            c0 -= 1;
+        }
+
+        /* Compute ranks of type B* substrings. */
+        let mut i = m - 1;
+        while 0 <= i {
+            if 0 <= sa[i as usize] {
+                let j = i;
+                loop {
+                    sa[(isab + sa[i as usize] as isize) as usize] = i as i32;
+                    i -= 1;
+                    if !(0 <= i && 0 <= sa[i as usize]) {
+                        break;
+                    }
+                }
+                sa[(i + 1) as usize] = (i - j) as i32;
+                if i <= 0 {
+                    break;
+                }
+            }
+            let j = i;
+            loop {
+                sa[i as usize] = !sa[i as usize];
+                sa[(isab + sa[i as usize] as isize) as usize] = j as i32;
+                i -= 1;
+                if !(sa[i as usize] < 0) {
+                    break;
+                }
+            }
+            sa[(isab + sa[i as usize] as isize) as usize] = j as i32;
+            i -= 1;
+        }
+
+        /* Construct the inverse suffix array of type B* suffixes using
+        trsort. */
+        trsort(sa, isab, m, 1);
+
+        /* Set the sorted order of type B* suffixes. */
+        let mut i = n - 1;
+        let mut j = m;
+        let mut c0 = t[(n - 1) as usize] as i32;
+        while 0 <= i {
+            i -= 1;
+            let mut c1 = c0;
+            while 0 <= i {
+                c0 = t[i as usize] as i32;
+                if !(c0 >= c1) {
+                    break;
+                }
+                i -= 1;
+                c1 = c0;
+            }
+            if 0 <= i {
+                let t0 = i;
+                i -= 1;
+                c1 = c0;
+                while 0 <= i {
+                    c0 = t[i as usize] as i32;
+                    if !(c0 <= c1) {
+                        break;
+                    }
+                    i -= 1;
+                    c1 = c0;
+                }
+                j -= 1;
+                sa[sa[(isab + j) as usize] as usize] = if t0 == 0 || 1 < t0 - i {
+                    t0 as i32
+                } else {
+                    !(t0 as i32)
+                };
+            }
+        }
+
+        /* Calculate the index of start/end point of each bucket. */
+        bucket_b[bb(ALPHABET_SIZE - 1, ALPHABET_SIZE - 1)] = n as i32; /* end point */
+        let mut k = m - 1;
+        let mut c0 = ALPHABET_SIZE - 2;
+        while 0 <= c0 {
+            let mut i = bucket_a[(c0 + 1) as usize] as isize - 1;
+            let mut c1 = ALPHABET_SIZE - 1;
+            while c0 < c1 {
+                let t0 = i - bucket_b[bb(c0, c1)] as isize;
+                bucket_b[bb(c0, c1)] = i as i32; /* end point */
+
+                /* Move all type B* suffixes to the correct position. */
+                i = t0;
+                let j = bucket_b[bstar(c0, c1)] as isize;
+                while j <= k {
+                    sa[i as usize] = sa[k as usize];
+                    i -= 1;
+                    k -= 1;
+                }
+                c1 -= 1;
+            }
+            bucket_b[bstar(c0, c0 + 1)] = (i - bucket_b[bb(c0, c0)] as isize + 1) as i32; /* start point */
+            bucket_b[bb(c0, c0)] = i as i32; /* end point */
+            c0 -= 1;
+        }
+    }
+
+    m
+}
+
+/* Constructs the suffix array by using the sorted order of type B*
+ * suffixes. */
+fn construct_sa(
+    t: &[u8],
+    sa: &mut [i32],
+    bucket_a: &mut [i32],
+    bucket_b: &mut [i32],
+    n: isize,
+    m: isize,
+) {
+    if 0 < m {
+        /* Construct the sorted order of type B suffixes by using
+        the sorted order of type B* suffixes. */
+        let mut c1 = ALPHABET_SIZE - 2;
+        while 0 <= c1 {
+            /* Scan the suffix array from right to left. */
+            let i = bucket_b[bstar(c1, c1 + 1)] as isize;
+            let mut j = bucket_a[(c1 + 1) as usize] as isize - 1;
+            let mut k: isize = 0;
+            let mut c2: i32 = -1;
+            while i <= j {
+                let mut s = sa[j as usize];
+                if 0 < s {
+                    debug_assert_eq!(t[s as usize] as i32, c1);
+                    debug_assert!((s as isize + 1) < n && t[s as usize] <= t[(s + 1) as usize]);
+                    debug_assert!(t[(s - 1) as usize] <= t[s as usize]);
+                    sa[j as usize] = !s;
+                    s -= 1;
+                    let c0 = t[s as usize] as i32;
+                    if 0 < s && (t[(s - 1) as usize] as i32) > c0 {
+                        s = !s;
+                    }
+                    if c0 != c2 {
+                        if 0 <= c2 {
+                            bucket_b[bb(c2, c1)] = k as i32;
+                        }
+                        c2 = c0;
+                        k = bucket_b[bb(c2, c1)] as isize;
+                    }
+                    debug_assert!(k < j);
+                    sa[k as usize] = s;
+                    k -= 1;
+                } else {
+                    debug_assert!((s == 0 && t[s as usize] as i32 == c1) || s < 0);
+                    sa[j as usize] = !s;
+                }
+                j -= 1;
+            }
+            c1 -= 1;
+        }
+    }
+
+    /* Construct the suffix array by using the sorted order of type B
+    suffixes. */
+    let mut c2 = t[(n - 1) as usize] as i32;
+    let mut k = bucket_a[c2 as usize] as isize;
+    sa[k as usize] = if (t[(n - 2) as usize] as i32) < c2 {
+        !((n - 1) as i32)
+    } else {
+        (n - 1) as i32
+    };
+    k += 1;
+    /* Scan the suffix array from left to right. */
+    let mut i: isize = 0;
+    let j = n;
+    while i < j {
+        let mut s = sa[i as usize];
+        if 0 < s {
+            debug_assert!(t[(s - 1) as usize] >= t[s as usize]);
+            s -= 1;
+            let c0 = t[s as usize] as i32;
+            if s == 0 || (t[(s - 1) as usize] as i32) < c0 {
+                s = !s;
+            }
+            if c0 != c2 {
+                bucket_a[c2 as usize] = k as i32;
+                c2 = c0;
+                k = bucket_a[c2 as usize] as isize;
+            }
+            debug_assert!(i < k);
+            sa[k as usize] = s;
+            k += 1;
+        } else {
+            debug_assert!(s < 0);
+            sa[i as usize] = !s;
+        }
+        i += 1;
+    }
+}
+
+/* --------------------------------------------------------------------- */
+
+/// Rust implementation of the `divsufsort()` entry point used by
+/// `ZDICT_trainFromBuffer_legacy()`.
+///
+/// Integration removes the C function body, so this direct export provides
+/// the existing library symbol without a wrapper.  The `open_mp` parameter is
+/// accepted for signature compatibility only: zstd never defines
+/// `LIBBSC_OPENMP`, so the C implementation ignored it as well.
+///
+/// Returns 0 on success, -1 for invalid arguments, and -2 when the bucket
+/// work arrays cannot be allocated, exactly like the C routine.
+#[no_mangle]
+pub unsafe extern "C" fn divsufsort(
+    t: *const u8,
+    sa: *mut c_int,
+    n: c_int,
+    open_mp: c_int,
+) -> c_int {
+    let _ = open_mp;
+
+    /* Check arguments. */
+    if t.is_null() || sa.is_null() || n < 0 {
+        return -1;
+    }
+    if n == 0 {
+        return 0;
+    }
+
+    let text = unsafe { slice::from_raw_parts(t, n as usize) };
+    let suffix = unsafe { slice::from_raw_parts_mut(sa, n as usize) };
+    if n == 1 {
+        suffix[0] = 0;
+        return 0;
+    }
+    if n == 2 {
+        let m = usize::from(text[0] < text[1]);
+        suffix[m ^ 1] = 0;
+        suffix[m] = 1;
+        return 0;
+    }
+
+    let mut bucket_a: Vec<i32> = Vec::new();
+    let mut bucket_b: Vec<i32> = Vec::new();
+    if bucket_a.try_reserve_exact(BUCKET_A_SIZE).is_err()
+        || bucket_b.try_reserve_exact(BUCKET_B_SIZE).is_err()
+    {
+        /* Match the C implementation's -2 result when malloc fails. */
+        return -2;
+    }
+    bucket_a.resize(BUCKET_A_SIZE, 0);
+    bucket_b.resize(BUCKET_B_SIZE, 0);
+
+    /* Suffixsort. */
+    let m = sort_type_bstar(text, suffix, &mut bucket_a, &mut bucket_b, n as isize);
+    construct_sa(text, suffix, &mut bucket_a, &mut bucket_b, n as isize, m);
+    0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::ptr;
+
+    fn build_sa(text: &[u8]) -> Vec<i32> {
+        let mut sa = vec![0i32; text.len()];
+        let result = unsafe { divsufsort(text.as_ptr(), sa.as_mut_ptr(), text.len() as c_int, 0) };
+        assert_eq!(result, 0);
+        sa
+    }
+
+    /// Trivial O(n^2 log n) reference: sort the suffix start positions by the
+    /// suffixes themselves.
+    fn reference_sa(text: &[u8]) -> Vec<i32> {
+        let mut sa: Vec<i32> = (0..text.len() as i32).collect();
+        sa.sort_by(|&a, &b| text[a as usize..].cmp(&text[b as usize..]));
+        sa
+    }
+
+    /// Suffix-array invariants: a permutation of `0..n` whose suffixes are in
+    /// strictly increasing lexicographic order.
+    fn assert_valid_sa(text: &[u8], sa: &[i32]) {
+        assert_eq!(sa.len(), text.len());
+        let mut seen = vec![false; text.len()];
+        for &p in sa {
+            let p = usize::try_from(p).expect("suffix index must be non-negative");
+            assert!(p < text.len(), "suffix index {p} out of range");
+            assert!(!seen[p], "duplicate suffix index {p}");
+            seen[p] = true;
+        }
+        for pair in sa.windows(2) {
+            assert!(
+                text[pair[0] as usize..] < text[pair[1] as usize..],
+                "suffixes {} and {} are not in sorted order",
+                pair[0],
+                pair[1]
+            );
+        }
+    }
+
+    /// Fixed-seed numerical-recipes LCG, used to generate reproducible
+    /// pseudo-random sample buffers.
+    fn lcg_bytes(len: usize, seed: u32, alphabet: u32) -> Vec<u8> {
+        let mut state = seed;
+        (0..len)
+            .map(|_| {
+                state = state.wrapping_mul(1_664_525).wrapping_add(1_013_904_223);
+                ((state >> 24) % alphabet) as u8
+            })
+            .collect()
+    }
+
+    #[test]
+    fn rejects_invalid_arguments() {
+        let text = [0u8; 1];
+        let mut sa = [0i32; 1];
+        assert_eq!(
+            unsafe { divsufsort(ptr::null(), sa.as_mut_ptr(), 1, 0) },
+            -1
+        );
+        assert_eq!(
+            unsafe { divsufsort(text.as_ptr(), ptr::null_mut(), 1, 0) },
+            -1
+        );
+        assert_eq!(
+            unsafe { divsufsort(text.as_ptr(), sa.as_mut_ptr(), -1, 0) },
+            -1
+        );
+    }
+
+    #[test]
+    fn sorts_trivial_inputs() {
+        /* empty */
+        let text = [0u8; 1];
+        let mut sa = [i32::MIN; 1];
+        assert_eq!(
+            unsafe { divsufsort(text.as_ptr(), sa.as_mut_ptr(), 0, 0) },
+            0
+        );
+        assert_eq!(sa[0], i32::MIN, "n == 0 must not touch the output");
+
+        /* single byte */
+        assert_eq!(build_sa(b"z"), [0]);
+
+        /* two bytes: ascending, descending, and equal */
+        assert_eq!(build_sa(b"ab"), [0, 1]);
+        assert_eq!(build_sa(b"ba"), [1, 0]);
+        assert_eq!(build_sa(b"aa"), [1, 0]);
+    }
+
+    #[test]
+    fn sorts_all_equal_bytes() {
+        let text = vec![b'q'; 10_000];
+        let sa = build_sa(&text);
+        /* For a constant text the shortest suffix sorts first. */
+        let expected: Vec<i32> = (0..text.len() as i32).rev().collect();
+        assert_eq!(sa, expected);
+    }
+
+    #[test]
+    fn sorts_abracadabra_exactly() {
+        /* Hand-computed: a(10) abra(7) abracadabra(0) acadabra(3) adabra(5)
+         * bra(8) bracadabra(1) cadabra(4) dabra(6) ra(9) racadabra(2). */
+        assert_eq!(build_sa(b"abracadabra"), [10, 7, 0, 3, 5, 8, 1, 4, 6, 9, 2]);
+    }
+
+    #[test]
+    fn matches_reference_on_periodic_text() {
+        /* Tandem repeats exercise trsort's repeat partitioning. */
+        let text: Vec<u8> = b"ab".iter().copied().cycle().take(4096).collect();
+        let sa = build_sa(&text);
+        assert_valid_sa(&text, &sa);
+        assert_eq!(sa, reference_sa(&text));
+    }
+
+    #[test]
+    fn matches_reference_on_random_bytes() {
+        let text = lcg_bytes(8192, 0x0BAD_5EED, 256);
+        let sa = build_sa(&text);
+        assert_valid_sa(&text, &sa);
+        assert_eq!(sa, reference_sa(&text));
+    }
+
+    #[test]
+    fn matches_reference_on_low_alphabet_text() {
+        /* A four-symbol alphabet produces the large first-two-character
+         * buckets that reach sssort's block merging and the deeper trsort
+         * paths. */
+        let text = lcg_bytes(16_384, 0xDEAD_BEEF, 4);
+        let sa = build_sa(&text);
+        assert_valid_sa(&text, &sa);
+        assert_eq!(sa, reference_sa(&text));
+    }
+}
@@ -5,6 +5,8 @@ pub mod bitstream;
 pub mod common;
 pub mod cpu;
 pub mod debug;
+#[cfg(feature = "dict-builder")]
+pub mod divsufsort;
 pub mod entropy_common;
 pub mod errors;
 #[cfg(feature = "compression")]
@@ -210,6 +210,7 @@ struct Cli {
    mmap_dict: i32,
    progress: i32,
    workers: Option<i32>,
+    single_thread: bool,
    block_size: Option<usize>,
    mem_limit: Option<u32>,
    ldm: bool,
@@ -254,6 +255,7 @@ impl Cli {
            mmap_dict: ZSTD_PS_AUTO,
            progress: FIO_PS_AUTO,
            workers: None,
+            single_thread: false,
            block_size: None,
            mem_limit: None,
            ldm: false,
@@ -332,8 +334,11 @@ unsafe fn default_worker_count() -> i32 {
 }

 #[cfg(feature = "compression")]
-unsafe fn resolved_worker_count(workers: Option<i32>) -> i32 {
+unsafe fn resolved_worker_count(workers: Option<i32>, single_thread: bool) -> i32 {
    match workers {
+        /* --single-thread pins zero workers; a bare zero (-T0 or the zstdmt
+         * program name) auto-detects the core count as in the C CLI. */
+        Some(0) if single_thread => 0,
        Some(0) => unsafe { UTIL_countPhysicalCores() }.max(1),
        Some(workers) => workers,
        None => unsafe { default_worker_count() },
@@ -385,7 +390,7 @@ fn usage(advanced: bool) {
        let _ = writeln!(out, "\nImplemented advanced compression controls:");
        let _ = writeln!(
            out,
-            "  --fast[=#], --ultra, --long[=#], --threads=#, --block-size=#"
+            "  --fast[=#], --ultra, --long[=#], --threads=#, --single-thread, --block-size=#"
        );
        let _ = writeln!(
            out,
@@ -638,6 +643,7 @@ fn parse_long_option(
                | "--no-row-match-finder"
                | "--row-match-finder"
                | "--rsyncable"
+                | "--single-thread"
                | "--compress-literals"
                | "--no-compress-literals"
                | "--exclude-compressed"
@@ -809,6 +815,14 @@ fn parse_long_option(
            cli.workers = Some(parse_worker_count(&value)?);
            Ok(None)
        }
+        "--single-thread" => {
+            /* As in the C CLI: zero workers plus a latch that suppresses the
+             * automatic core-count resolution, so fileio runs its
+             * single-thread streaming mode (slightly different from -T1). */
+            cli.workers = Some(0);
+            cli.single_thread = true;
+            Ok(None)
+        }
        "--memlimit" | "--memory" | "--memlimit-decompress" => {
            let value = next_value(attached, args, index, name)?;
            cli.mem_limit = Some(parse_u32(&value, "memory limit")?);
@@ -854,7 +868,6 @@ fn parse_long_option(
        | "--trace"
        | "--format"
        | "--priority"
-        | "--single-thread"
        | "--auto-threads"
        | "--fake-stdin-is-console"
        | "--fake-stdout-is-console"
@@ -1012,7 +1025,7 @@ unsafe fn apply_preferences(cli: &Cli, prefs: *mut FIO_prefs_t, ctx: *mut FIO_ct
                }),
        );
        #[cfg(feature = "compression")]
-        FIO_setNbWorkers(prefs, resolved_worker_count(cli.workers));
+        FIO_setNbWorkers(prefs, resolved_worker_count(cli.workers, cli.single_thread));
        FIO_setLdmFlag(prefs, u32::from(cli.ldm));
        FIO_setAdaptiveMode(prefs, i32::from(cli.adapt));
        FIO_setRsyncable(prefs, i32::from(cli.rsyncable));
@@ -1502,6 +1515,36 @@ mod tests {
        let cli = parse(&["zstdmt", "input"]);

        assert_eq!(cli.workers, Some(0));
+        assert!(!cli.single_thread);
+    }
+
+    #[test]
+    fn single_thread_pins_zero_workers() {
+        let cli = parse(&["zstd", "--single-thread", "input"]);
+
+        assert_eq!(cli.workers, Some(0));
+        assert!(cli.single_thread);
+    }
+
+    #[test]
+    fn a_later_thread_count_overrides_single_thread_workers() {
+        /* Mirrors the C CLI: -T after --single-thread wins the worker count,
+         * while the single-thread latch stays set. */
+        let cli = parse(&["zstd", "--single-thread", "-T2", "input"]);
+
+        assert_eq!(cli.workers, Some(2));
+        assert!(cli.single_thread);
+    }
+
+    #[test]
+    fn single_thread_rejects_attached_values() {
+        let error = parse_args(vec![
+            OsString::from("zstd"),
+            OsString::from("--single-thread=1"),
+        ])
+        .expect_err("an attached value must not activate --single-thread");
+
+        assert!(error.contains("does not take an argument"));
    }

    #[test]
@@ -79,6 +79,8 @@ RUST_TARGET_DIR := $(RUST_DIR)/target/$(RUST_BUILD_CONFIG)
 RUST_STATICLIB := $(RUST_TARGET_DIR)/release/libzstd_rs.a
 RUST_TARGET_32 ?= i686-unknown-linux-gnu
 RUST_STATICLIB_32 := $(RUST_TARGET_DIR)/$(RUST_TARGET_32)/release/libzstd_rs.a
+# Tests build every library module, so they use the crate's default feature
+# set (compression, decompression, and dict-builder) plus any forced HUF mode.
 RUST_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
                    --target-dir $(RUST_TARGET_DIR)
 ifneq ($(RUST_HUF_FEATURE),)