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update targetCBlockSize documentation

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This commit is contained in:
Yann Collet
2024-03-18 12:04:02 -07:00
parent cd4dba74de
commit f5728da365
2 changed files with 22 additions and 20 deletions
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lib/compress/zstd_compress_superblock.c
+1 -3
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@@ -469,8 +469,6 @@ static size_t sizeBlockSequences(const seqDef* sp, size_t nbSeqs,
return n; return n;
} }
#define CBLOCK_TARGET_SIZE_MIN 1340 /* suitable to fit into an ethernet / wifi / 4G transport frame */
/** ZSTD_compressSubBlock_multi() : /** ZSTD_compressSubBlock_multi() :
* Breaks super-block into multiple sub-blocks and compresses them. * Breaks super-block into multiple sub-blocks and compresses them.
* Entropy will be written into the first block. * Entropy will be written into the first block.
@@ -504,7 +502,7 @@ static size_t ZSTD_compressSubBlock_multi(const seqStore_t* seqStorePtr,
const BYTE* llCodePtr = seqStorePtr->llCode; const BYTE* llCodePtr = seqStorePtr->llCode;
const BYTE* mlCodePtr = seqStorePtr->mlCode; const BYTE* mlCodePtr = seqStorePtr->mlCode;
const BYTE* ofCodePtr = seqStorePtr->ofCode; const BYTE* ofCodePtr = seqStorePtr->ofCode;
size_t const minTarget = CBLOCK_TARGET_SIZE_MIN; /* enforce minimum size, to reduce undesirable side effects */ size_t const minTarget = ZSTD_TARGETCBLOCKSIZE_MIN; /* enforce minimum size, to reduce undesirable side effects */
size_t const targetCBlockSize = MAX(minTarget, cctxParams->targetCBlockSize); size_t const targetCBlockSize = MAX(minTarget, cctxParams->targetCBlockSize);
int writeLitEntropy = (entropyMetadata->hufMetadata.hType == set_compressed); int writeLitEntropy = (entropyMetadata->hufMetadata.hType == set_compressed);
int writeSeqEntropy = 1; int writeSeqEntropy = 1;
lib/zstd.h
+21 -17
View File
@@ -262,9 +262,9 @@ ZSTDLIB_API size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx); /* accept NULL pointer *
/*! ZSTD_compressCCtx() : /*! ZSTD_compressCCtx() :
* Same as ZSTD_compress(), using an explicit ZSTD_CCtx. * Same as ZSTD_compress(), using an explicit ZSTD_CCtx.
* Important : in order to behave similarly to `ZSTD_compress()`, * Important : in order to mirror `ZSTD_compress()` behavior,
* this function compresses at requested compression level, * this function compresses at the requested compression level,
* __ignoring any other parameter__ . * __ignoring any other advanced parameter__ .
* If any advanced parameter was set using the advanced API, * If any advanced parameter was set using the advanced API,
* they will all be reset. Only `compressionLevel` remains. * they will all be reset. Only `compressionLevel` remains.
*/ */
@@ -286,7 +286,7 @@ ZSTDLIB_API size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx); /* accept NULL pointer *
/*! ZSTD_decompressDCtx() : /*! ZSTD_decompressDCtx() :
* Same as ZSTD_decompress(), * Same as ZSTD_decompress(),
* requires an allocated ZSTD_DCtx. * requires an allocated ZSTD_DCtx.
* Compatible with sticky parameters. * Compatible with sticky parameters (see below).
*/ */
ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx, ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
void* dst, size_t dstCapacity, void* dst, size_t dstCapacity,
@@ -302,12 +302,12 @@ ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
* using ZSTD_CCtx_set*() functions. * using ZSTD_CCtx_set*() functions.
* Pushed parameters are sticky : they are valid for next compressed frame, and any subsequent frame. * Pushed parameters are sticky : they are valid for next compressed frame, and any subsequent frame.
* "sticky" parameters are applicable to `ZSTD_compress2()` and `ZSTD_compressStream*()` ! * "sticky" parameters are applicable to `ZSTD_compress2()` and `ZSTD_compressStream*()` !
* __They do not apply to "simple" one-shot variants such as ZSTD_compressCCtx()__ . * __They do not apply to one-shot variants such as ZSTD_compressCCtx()__ .
* *
* It's possible to reset all parameters to "default" using ZSTD_CCtx_reset(). * It's possible to reset all parameters to "default" using ZSTD_CCtx_reset().
* *
* This API supersedes all other "advanced" API entry points in the experimental section. * This API supersedes all other "advanced" API entry points in the experimental section.
* In the future, we expect to remove from experimental API entry points which are redundant with this API. * In the future, we expect to remove API entry points from experimental which are redundant with this API.
*/ */
@@ -390,16 +390,19 @@ typedef enum {
* The higher the value of selected strategy, the more complex it is, * The higher the value of selected strategy, the more complex it is,
* resulting in stronger and slower compression. * resulting in stronger and slower compression.
* Special: value 0 means "use default strategy". */ * Special: value 0 means "use default strategy". */
ZSTD_c_targetCBlockSize=130, /* Tries to fit compressed block size to be
* around targetCBlockSize. No target when ZSTD_c_targetCBlockSize=130, /* v1.5.6+
* targetCBlockSize == 0. There is no guarantee * Attempts to fit compressed block size into approximatively targetCBlockSize.
* on compressed block size (default:0). * Bound by ZSTD_TARGETCBLOCKSIZE_MIN and ZSTD_TARGETCBLOCKSIZE_MAX.
* Since the decoder has to buffer a complete * Note that it's not a guarantee, just a convergence target (default:0).
* block to begin decoding it, in low band- * No target when targetCBlockSize == 0.
* width streaming environments this may * This is helpful in low bandwidth streaming environments to improve end-to-end latency,
* improve end-to-end latency. Bound by * when a client can make use of partial documents (a prominent example being Chrome).
* ZSTD_TARGETCBLOCKSIZE_MIN and * Note: this parameter is stable since v1.5.6.
* ZSTD_TARGETCBLOCKSIZE_MAX. */ * It was present as an experimental parameter in earlier versions,
* but we don't recomment using it with earlier library versions
* due to massive performance regressions.
*/
/* LDM mode parameters */ /* LDM mode parameters */
ZSTD_c_enableLongDistanceMatching=160, /* Enable long distance matching. ZSTD_c_enableLongDistanceMatching=160, /* Enable long distance matching.
* This parameter is designed to improve compression ratio * This parameter is designed to improve compression ratio
@@ -584,6 +587,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset);
/*! ZSTD_compress2() : /*! ZSTD_compress2() :
* Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API. * Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API.
* (note that this entry point doesn't even expose a compression level parameter).
* ZSTD_compress2() always starts a new frame. * ZSTD_compress2() always starts a new frame.
* Should cctx hold data from a previously unfinished frame, everything about it is forgotten. * Should cctx hold data from a previously unfinished frame, everything about it is forgotten.
* - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() * - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
@@ -1250,7 +1254,7 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
#define ZSTD_LDM_HASHRATELOG_MAX (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN) #define ZSTD_LDM_HASHRATELOG_MAX (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN)
/* Advanced parameter bounds */ /* Advanced parameter bounds */
#define ZSTD_TARGETCBLOCKSIZE_MIN 64 #define ZSTD_TARGETCBLOCKSIZE_MIN 1340 /* suitable to fit into an ethernet / wifi / 4G transport frame */
#define ZSTD_TARGETCBLOCKSIZE_MAX ZSTD_BLOCKSIZE_MAX #define ZSTD_TARGETCBLOCKSIZE_MAX ZSTD_BLOCKSIZE_MAX
#define ZSTD_SRCSIZEHINT_MIN 0 #define ZSTD_SRCSIZEHINT_MIN 0
#define ZSTD_SRCSIZEHINT_MAX INT_MAX #define ZSTD_SRCSIZEHINT_MAX INT_MAX