Merge pull request #2829 from facebook/ZSTD_DECODER_INTERNAL_BUFFER

minor : change build macro to ZSTD_DECODER_INTERNAL_BUFFER

lib/README.md

@@ -155,11 +155,11 @@ The file structure is designed to make this selection manually achievable for an
 - The build macro `ZSTD_NO_INTRINSICS` can be defined to disable all explicit intrinsics.
   Compiler builtins are still used.
 
-- The build macro `ZSTD_LITBUFFEREXTRASIZE` can be set to control the amount of extra memory used
-  during decompression to store literals.  This defaults to 64kB.  Reducing it can reduce the
-  memory footprint required for decompression by increasing the portion of the literal buffer that
-  is stored in the unwritten portion of the dst buffer, at the cost of performance impact for
-  decompression.
+- The build macro `ZSTD_DECODER_INTERNAL_BUFFER` can be set to control
+  the amount of extra memory used during decompression to store literals.
+  This defaults to 64kB.  Reducing this value reduces the memory footprint of
+  `ZSTD_DCtx` decompression contexts,
+  but might also result in a small decompression speed cost.
 
 
 #### Windows : using MinGW+MSYS to create DLL

lib/common/zstd_internal.h

@@ -57,6 +57,7 @@ extern "C" {
 #undef MAX
 #define MIN(a,b) ((a)<(b) ? (a) : (b))
 #define MAX(a,b) ((a)>(b) ? (a) : (b))
+#define BOUNDED(min,val,max) (MAX(min,MIN(val,max)))
 
 
 /*-*************************************

lib/compress/zstd_compress.c

@@ -1465,7 +1465,7 @@ static size_t ZSTD_estimateCCtxSize_usingCCtxParams_internal(
         const size_t buffOutSize,
         const U64 pledgedSrcSize)
 {
-    size_t const windowSize = MAX(1, (size_t)MIN(((U64)1 << cParams->windowLog), pledgedSrcSize));
+    size_t const windowSize = (size_t) BOUNDED(1ULL, 1ULL << cParams->windowLog, pledgedSrcSize);
     size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, windowSize);
     U32    const divider = (cParams->minMatch==3) ? 3 : 4;
     size_t const maxNbSeq = blockSize / divider;
@@ -1783,7 +1783,7 @@ ZSTD_reset_matchState(ZSTD_matchState_t* ms,
             if (ms->tagTable) ZSTD_memset(ms->tagTable, 0, tagTableSize);
         }
         {   /* Switch to 32-entry rows if searchLog is 5 (or more) */
-            U32 const rowLog = MAX(MIN(cParams->searchLog, 6), 4);
+            U32 const rowLog = BOUNDED(4, cParams->searchLog, 6);
             assert(cParams->hashLog >= rowLog);
             ms->rowHashLog = cParams->hashLog - rowLog;
         }

lib/compress/zstd_lazy.c

@@ -974,7 +974,7 @@ FORCE_INLINE_TEMPLATE void ZSTD_row_update_internal(ZSTD_matchState_t* ms, const
  * processing.
  */
 void ZSTD_row_update(ZSTD_matchState_t* const ms, const BYTE* ip) {
-    const U32 rowLog = MAX(MIN(ms->cParams.searchLog, 6), 4);
+    const U32 rowLog = BOUNDED(4, ms->cParams.searchLog, 6);
     const U32 rowMask = (1u << rowLog) - 1;
     const U32 mls = MIN(ms->cParams.minMatch, 6 /* mls caps out at 6 */);
 

lib/decompress/zstd_decompress.c

@@ -1123,7 +1123,7 @@ static size_t ZSTD_nextSrcSizeToDecompressWithInputSize(ZSTD_DCtx* dctx, size_t
         return dctx->expected;
     if (dctx->bType != bt_raw)
         return dctx->expected;
-    return MIN(MAX(inputSize, 1), dctx->expected);
+    return BOUNDED(1, inputSize, dctx->expected);
 }
 
 ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx) {

lib/decompress/zstd_decompress_internal.h

@@ -106,10 +106,16 @@ typedef struct {
     size_t ddictPtrCount;
 } ZSTD_DDictHashSet;
 
-#ifndef ZSTD_LITBUFFEREXTRASIZE
-#define ZSTD_LITBUFFEREXTRASIZE    (1 << 16) /* extra buffer reduces amount of dst required to store litBuffer */
+#ifndef ZSTD_DECODER_INTERNAL_BUFFER
+#  define ZSTD_DECODER_INTERNAL_BUFFER  (1 << 16)
 #endif
 
+#define ZSTD_LBMIN 64
+#define ZSTD_LBMAX (128 << 10)
+
+/* extra buffer, compensates when dst is not large enough to store litBuffer */
+#define ZSTD_LITBUFFEREXTRASIZE  BOUNDED(ZSTD_LBMIN, ZSTD_DECODER_INTERNAL_BUFFER, ZSTD_LBMAX)
+
 typedef enum {
     ZSTD_not_in_dst = 0,  /* Stored entirely within litExtraBuffer */
     ZSTD_in_dst = 1,           /* Stored entirely within dst (in memory after current output write) */