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Update Comment on ZSTD_estimateCCtxSize()

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This commit is contained in:
W. Felix Handte 2019-09-20 14:11:29 -04:00
parent dd2838eeb4
commit f7d9b36835
2 changed files with 20 additions and 11 deletions
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25
lib/zstd.h
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@ -1221,14 +1221,23 @@ ZSTDLIB_API size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
***************************************/
/*! ZSTD_estimate*() :
* These functions make it possible to estimate memory usage
* of a future {D,C}Ctx, before its creation.
* ZSTD_estimateCCtxSize() will provide a budget large enough for any compression level up to selected one.
* It will also consider src size to be arbitrarily "large", which is worst case.
* If srcSize is known to always be small, ZSTD_estimateCCtxSize_usingCParams() can provide a tighter estimation.
* ZSTD_estimateCCtxSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
* ZSTD_estimateCCtxSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1.
* Note : CCtx size estimation is only correct for single-threaded compression. */
* These functions make it possible to estimate memory usage of a future
* {D,C}Ctx, before its creation.
*
* ZSTD_estimateCCtxSize() will provide a budget large enough for any
* compression level up to selected one. Unlike ZSTD_estimateCStreamSize*(),
* this estimate does not include space for a window buffer, so this estimate
* is guaranteed to be enough for single-shot compressions, but not streaming
* compressions. It will however assume the input may be arbitrarily large,
* which is the worst case. If srcSize is known to always be small,
* ZSTD_estimateCCtxSize_usingCParams() can provide a tighter estimation.
* ZSTD_estimateCCtxSize_usingCParams() can be used in tandem with
* ZSTD_getCParams() to create cParams from compressionLevel.
* ZSTD_estimateCCtxSize_usingCCtxParams() can be used in tandem with
* ZSTD_CCtxParams_setParameter().
*
* Note: only single-threaded compression is supported. This function will
* return an error code if ZSTD_c_nbWorkers is >= 1. */
ZSTDLIB_API size_t ZSTD_estimateCCtxSize(int compressionLevel);
ZSTDLIB_API size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
ZSTDLIB_API size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);

6
tests/fuzzer.c
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@ -2156,9 +2156,9 @@ static int basicUnitTests(U32 const seed, double compressibility)
size_t approxIndex = 0;
size_t maxIndex = ((3U << 29) + (1U << ZSTD_WINDOWLOG_MAX)); /* ZSTD_CURRENT_MAX from zstd_compress_internal.h */
/* vastly overprovision space in a static context so that we can do all
* this without ever reallocating, which would reset the indices */
size_t const staticCCtxSize = 2 * ZSTD_estimateCCtxSize(22);
/* Provision enough space in a static context so that we can do all
* this without ever reallocating, which would reset the indices. */
size_t const staticCCtxSize = ZSTD_estimateCStreamSize(22);
void* const staticCCtxBuffer = malloc(staticCCtxSize);
ZSTD_CCtx* cctx = ZSTD_initStaticCCtx(staticCCtxBuffer, staticCCtxSize);