however it does mean that all frame data must be present and valid.
</p></pre><BR>
+<pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
+</b><p> `src` should point to the start of a ZSTD frame
+ `srcSize` must be >= ZSTD_frameHeaderSize_prefix.
+ @return : size of the Frame Header
+</p></pre><BR>
+
<a name="Chapter13"></a><h2>Context memory usage</h2><pre></pre>
<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
Object memory usage can evolve if it's re-used multiple times.
</p></pre><BR>
-<pre><b>size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
+<pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel);
+size_t ZSTD_estimateCCtxSize_advanced(ZSTD_compressionParameters cParams);
size_t ZSTD_estimateDCtxSize(void);
</b><p> These functions make it possible to estimate memory usage
- of a future target object, before its allocation,
- given a set of parameters, which vary depending on target object.
+ of a future {D,C}Ctx, before its creation.
The objective is to guide decision before allocation.
+ ZSTD_estimateCCtxSize() will consider src size to be arbitrarily "large".
+ If srcSize is known to be small, ZSTD_estimateCCtxSize_advanced() will provide a better (smaller) estimation.
+ ZSTD_estimateCCtxSize_advanced() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
Note : CCtx estimation is only correct for single-threaded compression
</p></pre><BR>
}
-size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams)
+size_t ZSTD_estimateCCtxSize_advanced(ZSTD_compressionParameters cParams)
{
size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, (size_t)1 << cParams.windowLog);
U32 const divider = (cParams.searchLength==3) ? 3 : 4;
return sizeof(ZSTD_CCtx) + neededSpace;
}
+size_t ZSTD_estimateCCtxSize(int compressionLevel)
+{
+ ZSTD_compressionParameters const cParams = ZSTD_getCParams(compressionLevel, 0, 0);
+ return ZSTD_estimateCCtxSize_advanced(cParams);
+}
+
size_t ZSTD_estimateCStreamSize(ZSTD_compressionParameters cParams)
{
- size_t const CCtxSize = ZSTD_estimateCCtxSize(cParams);
+ size_t const CCtxSize = ZSTD_estimateCCtxSize_advanced(cParams);
size_t const blockSize = MIN(ZSTD_BLOCKSIZE_MAX, (size_t)1 << cParams.windowLog);
size_t const inBuffSize = ((size_t)1 << cParams.windowLog) + blockSize;
size_t const outBuffSize = ZSTD_compressBound(blockSize) + 1;
size_t ZSTD_estimateCDictSize(ZSTD_compressionParameters cParams, size_t dictSize, unsigned byReference)
{
DEBUGLOG(5, "sizeof(ZSTD_CDict) : %u", (U32)sizeof(ZSTD_CDict));
- DEBUGLOG(5, "CCtx estimate : %u", (U32)ZSTD_estimateCCtxSize(cParams));
- return sizeof(ZSTD_CDict) + ZSTD_estimateCCtxSize(cParams)
+ DEBUGLOG(5, "CCtx estimate : %u", (U32)ZSTD_estimateCCtxSize_advanced(cParams));
+ return sizeof(ZSTD_CDict) + ZSTD_estimateCCtxSize_advanced(cParams)
+ (byReference ? 0 : dictSize);
}
unsigned byReference, ZSTD_dictMode_e dictMode,
ZSTD_compressionParameters cParams)
{
- size_t const cctxSize = ZSTD_estimateCCtxSize(cParams);
+ size_t const cctxSize = ZSTD_estimateCCtxSize_advanced(cParams);
size_t const neededSize = sizeof(ZSTD_CDict) + (byReference ? 0 : dictSize)
+ cctxSize;
ZSTD_CDict* const cdict = (ZSTD_CDict*) workspace;
/*! ZSTD_estimate*() :
* These functions make it possible to estimate memory usage
- * of a future target object, before its allocation,
- * given a set of parameters, which vary depending on target object.
+ * of a future {D,C}Ctx, before its creation.
* The objective is to guide decision before allocation.
+ * ZSTD_estimateCCtxSize() will consider src size to be arbitrarily "large".
+ * If srcSize is known to be small, ZSTD_estimateCCtxSize_advanced() will provide a better (smaller) estimation.
+ * ZSTD_estimateCCtxSize_advanced() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
* Note : CCtx estimation is only correct for single-threaded compression */
-ZSTDLIB_API size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
+ZSTDLIB_API size_t ZSTD_estimateCCtxSize(int compressionLevel);
+ZSTDLIB_API size_t ZSTD_estimateCCtxSize_advanced(ZSTD_compressionParameters cParams);
ZSTDLIB_API size_t ZSTD_estimateDCtxSize(void);
/*! ZSTD_estimate?StreamSize() :
double W_DMemUsed_note = W_ratioNote * ( 40 + 9*cLevel) - log((double)W_DMemUsed);
double O_DMemUsed_note = O_ratioNote * ( 40 + 9*cLevel) - log((double)O_DMemUsed);
- size_t W_CMemUsed = (1 << params.windowLog) + ZSTD_estimateCCtxSize(params);
- size_t O_CMemUsed = (1 << winners[cLevel].params.windowLog) + ZSTD_estimateCCtxSize(winners[cLevel].params);
+ size_t W_CMemUsed = (1 << params.windowLog) + ZSTD_estimateCCtxSize_advanced(params);
+ size_t O_CMemUsed = (1 << winners[cLevel].params.windowLog) + ZSTD_estimateCCtxSize_advanced(winners[cLevel].params);
double W_CMemUsed_note = W_ratioNote * ( 50 + 13*cLevel) - log((double)W_CMemUsed);
double O_CMemUsed_note = O_ratioNote * ( 50 + 13*cLevel) - log((double)O_CMemUsed);