refactor(ldm): expose parameter adjustment from Rust

Move the pure LDM parameter-defaulting policy behind the original
ZSTD_ldm_adjustParameters() ABI symbol. Rust now receives the existing C
parameter structs directly, applies the same 30/8/8 build constants, and
keeps the ASAN-sensitive table-size projection in C.

Test Plan:
- `cc -fsyntax-only -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -Ilib/legacy lib/compress/zstd_ldm.c` -- passed.
- `cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed.
- `git diff --check` and `git diff --cached --check` -- passed.
- Heavy verification intentionally deferred until the combined seam set is ready.

lib/compress/zstd_ldm.c

@@ -251,9 +251,6 @@ typedef char ZSTD_rust_ldm_rep_count[(ZSTD_REP_NUM == 3) ? 1 : -1];
 typedef char ZSTD_rust_ldm_strategy_values_check[
         (ZSTD_fast == 1 && ZSTD_dfast == 2 && ZSTD_btultra2 == 9) ? 1 : -1];
 
-void ZSTD_rust_ldm_adjustParameters(
-        void* params, U32 windowLog, int strategy,
-        U32 hashLogMax, U32 bucketSizeLogMax, int btultra);
 size_t ZSTD_rust_ldm_getTableSize(
         const void* params, int enableLdm, size_t redzoneSize);
 void ZSTD_rust_ldm_fillHashTable(
@@ -336,14 +333,6 @@ void ZSTD_ldm_rust_setLdmSeqStore(void* blockContext, const void* rawSeqStore)
     context->ms->ldmSeqStore = (const RawSeqStore_t*)rawSeqStore;
 }
 
-void ZSTD_ldm_adjustParameters(ldmParams_t* params,
-                               const ZSTD_compressionParameters* cParams)
-{
-    ZSTD_rust_ldm_adjustParameters(
-            params, cParams->windowLog, (int)cParams->strategy,
-            ZSTD_HASHLOG_MAX, ZSTD_LDM_BUCKETSIZELOG_MAX, (int)ZSTD_btultra);
-}
-
 size_t ZSTD_ldm_getTableSize(ldmParams_t params)
 {
 #if ZSTD_ADDRESS_SANITIZER && !defined(ZSTD_ASAN_DONT_POISON_WORKSPACE)

rust/src/zstd_ldm.rs

@@ -12,6 +12,7 @@
 use crate::errors::{ERR_isError, ZstdErrorCode, ERROR};
 use crate::mem::{MEM_64bits, MEM_isLittleEndian, MEM_read16, MEM_read32, MEM_readST};
 use crate::xxhash::XXH64;
+use crate::zstd_compress_params::ZSTD_compressionParameters;
 use crate::zstd_fast::store_seq_opaque;
 use std::ffi::c_void;
 use std::mem::size_of;
@@ -651,17 +652,14 @@ unsafe fn generate_sequences_internal(
     unsafe { iend.offset_from(anchor) as usize }
 }
 
-/// Rust implementation called by the C ABI wrapper for parameter adjustment.
+fn adjust_parameters(
-#[no_mangle]
+    params: &mut LdmParams,
-pub unsafe extern "C" fn ZSTD_rust_ldm_adjustParameters(
-    params: *mut c_void,
     window_log: u32,
     strategy: c_int,
     hash_log_max: u32,
     bucket_size_log_max: u32,
     btultra: c_int,
 ) {
-    let params = unsafe { &mut *params.cast::<LdmParams>() };
     params.window_log = window_log;
     if params.hash_rate_log == 0 {
         if params.hash_log > 0 {
@@ -691,6 +689,17 @@ pub unsafe extern "C" fn ZSTD_rust_ldm_adjustParameters(
     params.bucket_size_log = params.bucket_size_log.min(params.hash_log);
 }
 
+/// Adjust LDM parameters using the original C ABI.
+#[no_mangle]
+pub unsafe extern "C" fn ZSTD_ldm_adjustParameters(
+    params: *mut LdmParams,
+    c_params: *const ZSTD_compressionParameters,
+) {
+    let params = unsafe { &mut *params };
+    let c_params = unsafe { &*c_params };
+    adjust_parameters(params, c_params.windowLog, c_params.strategy, 30, 8, 8);
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn ZSTD_rust_ldm_getTableSize(
     params: *const c_void,
@@ -1069,16 +1078,12 @@ mod tests {
             hash_rate_log: 0,
             window_log: 0,
         };
-        unsafe {
+        let c_params = ZSTD_compressionParameters {
-            ZSTD_rust_ldm_adjustParameters(
+            windowLog: 20,
-                (&mut params as *mut LdmParams).cast::<c_void>(),
+            strategy: 3,
-                20,
+            ..Default::default()
-                3,
-                30,
-                8,
-                8,
-            )
         };
+        unsafe { ZSTD_ldm_adjustParameters(&mut params, &c_params) };
         assert_eq!(params.window_log, 20);
         assert_eq!(params.hash_rate_log, 6);
         assert_eq!(params.hash_log, 14);