1608 lines
97 KiB
HTML
1608 lines
97 KiB
HTML
<html>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>zstd 1.4.4 Manual</title>
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</head>
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<body>
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<h1>zstd 1.4.4 Manual</h1>
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<hr>
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<a name="Contents"></a><h2>Contents</h2>
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<ol>
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<li><a href="#Chapter1">Introduction</a></li>
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<li><a href="#Chapter2">Version</a></li>
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<li><a href="#Chapter3">Simple API</a></li>
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<li><a href="#Chapter4">Explicit context</a></li>
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<li><a href="#Chapter5">Advanced compression API</a></li>
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<li><a href="#Chapter6">Advanced decompression API</a></li>
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<li><a href="#Chapter7">Streaming</a></li>
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<li><a href="#Chapter8">Streaming compression - HowTo</a></li>
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<li><a href="#Chapter9">Streaming decompression - HowTo</a></li>
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<li><a href="#Chapter10">Simple dictionary API</a></li>
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<li><a href="#Chapter11">Bulk processing dictionary API</a></li>
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<li><a href="#Chapter12">Dictionary helper functions</a></li>
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<li><a href="#Chapter13">Advanced dictionary and prefix API</a></li>
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<li><a href="#Chapter14">experimental API (static linking only)</a></li>
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<li><a href="#Chapter15">Frame size functions</a></li>
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<li><a href="#Chapter16">Memory management</a></li>
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<li><a href="#Chapter17">Advanced compression functions</a></li>
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<li><a href="#Chapter18">Advanced decompression functions</a></li>
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<li><a href="#Chapter19">Advanced streaming functions</a></li>
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<li><a href="#Chapter20">Buffer-less and synchronous inner streaming functions</a></li>
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<li><a href="#Chapter21">Buffer-less streaming compression (synchronous mode)</a></li>
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<li><a href="#Chapter22">Buffer-less streaming decompression (synchronous mode)</a></li>
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<li><a href="#Chapter23">Block level API</a></li>
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</ol>
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<hr>
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<a name="Chapter1"></a><h2>Introduction</h2><pre>
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zstd, short for Zstandard, is a fast lossless compression algorithm, targeting
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real-time compression scenarios at zlib-level and better compression ratios.
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The zstd compression library provides in-memory compression and decompression
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functions.
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The library supports regular compression levels from 1 up to ZSTD_maxCLevel(),
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which is currently 22. Levels >= 20, labeled `--ultra`, should be used with
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caution, as they require more memory. The library also offers negative
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compression levels, which extend the range of speed vs. ratio preferences.
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The lower the level, the faster the speed (at the cost of compression).
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Compression can be done in:
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- a single step (described as Simple API)
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- a single step, reusing a context (described as Explicit context)
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- unbounded multiple steps (described as Streaming compression)
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The compression ratio achievable on small data can be highly improved using
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a dictionary. Dictionary compression can be performed in:
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- a single step (described as Simple dictionary API)
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- a single step, reusing a dictionary (described as Bulk-processing
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dictionary API)
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Advanced experimental functions can be accessed using
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`#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h.
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Advanced experimental APIs should never be used with a dynamically-linked
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library. They are not "stable"; their definitions or signatures may change in
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the future. Only static linking is allowed.
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<BR></pre>
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<a name="Chapter2"></a><h2>Version</h2><pre></pre>
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<pre><b>unsigned ZSTD_versionNumber(void); </b>/**< to check runtime library version */<b>
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</b></pre><BR>
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<a name="Chapter3"></a><h2>Simple API</h2><pre></pre>
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<pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
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const void* src, size_t srcSize,
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int compressionLevel);
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</b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
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Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
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@return : compressed size written into `dst` (<= `dstCapacity),
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or an error code if it fails (which can be tested using ZSTD_isError()).
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</p></pre><BR>
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<pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
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const void* src, size_t compressedSize);
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</b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames.
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`dstCapacity` is an upper bound of originalSize to regenerate.
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If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
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@return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
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or an errorCode if it fails (which can be tested using ZSTD_isError()).
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</p></pre><BR>
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<pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1)
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#define ZSTD_CONTENTSIZE_ERROR (0ULL - 2)
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unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
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</b><p> `src` should point to the start of a ZSTD encoded frame.
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`srcSize` must be at least as large as the frame header.
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hint : any size >= `ZSTD_frameHeaderSize_max` is large enough.
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@return : - decompressed size of `src` frame content, if known
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- ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
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- ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
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note 1 : a 0 return value means the frame is valid but "empty".
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note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode.
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When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
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In which case, it's necessary to use streaming mode to decompress data.
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Optionally, application can rely on some implicit limit,
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as ZSTD_decompress() only needs an upper bound of decompressed size.
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(For example, data could be necessarily cut into blocks <= 16 KB).
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note 3 : decompressed size is always present when compression is completed using single-pass functions,
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such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict().
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note 4 : decompressed size can be very large (64-bits value),
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potentially larger than what local system can handle as a single memory segment.
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In which case, it's necessary to use streaming mode to decompress data.
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note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified.
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Always ensure return value fits within application's authorized limits.
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Each application can set its own limits.
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note 6 : This function replaces ZSTD_getDecompressedSize()
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</p></pre><BR>
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<pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
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</b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize().
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Both functions work the same way, but ZSTD_getDecompressedSize() blends
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"empty", "unknown" and "error" results to the same return value (0),
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while ZSTD_getFrameContentSize() gives them separate return values.
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@return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise.
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</p></pre><BR>
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<pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
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</b><p> `src` should point to the start of a ZSTD frame or skippable frame.
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`srcSize` must be >= first frame size
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@return : the compressed size of the first frame starting at `src`,
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suitable to pass as `srcSize` to `ZSTD_decompress` or similar,
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or an error code if input is invalid
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</p></pre><BR>
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<h3>Helper functions</h3><pre></pre><b><pre>#define ZSTD_COMPRESSBOUND(srcSize) ((srcSize) + ((srcSize)>>8) + (((srcSize) < (128<<10)) ? (((128<<10) - (srcSize)) >> 11) </b>/* margin, from 64 to 0 */ : 0)) /* this formula ensures that bound(A) + bound(B) <= bound(A+B) as long as A and B >= 128 KB */<b>
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size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b>
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unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
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const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
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int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b>
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int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
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</pre></b><BR>
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<a name="Chapter4"></a><h2>Explicit context</h2><pre></pre>
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<h3>Compression context</h3><pre> When compressing many times,
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it is recommended to allocate a context just once,
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and re-use it for each successive compression operation.
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This will make workload friendlier for system's memory.
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Note : re-using context is just a speed / resource optimization.
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It doesn't change the compression ratio, which remains identical.
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Note 2 : In multi-threaded environments,
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use one different context per thread for parallel execution.
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</pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
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ZSTD_CCtx* ZSTD_createCCtx(void);
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size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
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</pre></b><BR>
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<pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx,
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void* dst, size_t dstCapacity,
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const void* src, size_t srcSize,
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int compressionLevel);
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</b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx
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The function will compress at requested compression level,
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ignoring any other parameter
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</p></pre><BR>
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<h3>Decompression context</h3><pre> When decompressing many times,
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it is recommended to allocate a context only once,
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and re-use it for each successive compression operation.
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This will make workload friendlier for system's memory.
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Use one context per thread for parallel execution.
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</pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
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ZSTD_DCtx* ZSTD_createDCtx(void);
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size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
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</pre></b><BR>
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<pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
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void* dst, size_t dstCapacity,
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const void* src, size_t srcSize);
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</b><p> Same as ZSTD_decompress(),
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requires an allocated ZSTD_DCtx.
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Compatible with sticky parameters.
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</p></pre><BR>
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<a name="Chapter5"></a><h2>Advanced compression API</h2><pre></pre>
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<pre><b>typedef enum { ZSTD_fast=1,
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ZSTD_dfast=2,
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ZSTD_greedy=3,
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ZSTD_lazy=4,
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ZSTD_lazy2=5,
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ZSTD_btlazy2=6,
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ZSTD_btopt=7,
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ZSTD_btultra=8,
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ZSTD_btultra2=9
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</b>/* note : new strategies _might_ be added in the future.<b>
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Only the order (from fast to strong) is guaranteed */
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} ZSTD_strategy;
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</b></pre><BR>
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<pre><b>typedef enum {
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</b>/* compression parameters<b>
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* Note: When compressing with a ZSTD_CDict these parameters are superseded
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* by the parameters used to construct the ZSTD_CDict. See ZSTD_CCtx_refCDict()
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* for more info (superseded-by-cdict). */
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ZSTD_c_compressionLevel=100, </b>/* Update all compression parameters according to pre-defined cLevel table<b>
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* Default level is ZSTD_CLEVEL_DEFAULT==3.
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* Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT.
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* Note 1 : it's possible to pass a negative compression level.
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* Note 2 : setting a level sets all default values of other compression parameters */
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ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b>
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* Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX.
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* Special: value 0 means "use default windowLog".
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* Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT
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* requires explicitly allowing such window size at decompression stage if using streaming. */
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ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b>
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* Resulting memory usage is (1 << (hashLog+2)).
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* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX.
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* Larger tables improve compression ratio of strategies <= dFast,
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* and improve speed of strategies > dFast.
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* Special: value 0 means "use default hashLog". */
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ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b>
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* Resulting memory usage is (1 << (chainLog+2)).
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* Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX.
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* Larger tables result in better and slower compression.
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* This parameter is useless when using "fast" strategy.
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* It's still useful when using "dfast" strategy,
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* in which case it defines a secondary probe table.
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* Special: value 0 means "use default chainLog". */
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ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b>
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* More attempts result in better and slower compression.
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* This parameter is useless when using "fast" and "dFast" strategies.
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* Special: value 0 means "use default searchLog". */
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ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b>
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* Note that Zstandard can still find matches of smaller size,
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* it just tweaks its search algorithm to look for this size and larger.
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* Larger values increase compression and decompression speed, but decrease ratio.
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* Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX.
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* Note that currently, for all strategies < btopt, effective minimum is 4.
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* , for all strategies > fast, effective maximum is 6.
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* Special: value 0 means "use default minMatchLength". */
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ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b>
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* For strategies btopt, btultra & btultra2:
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* Length of Match considered "good enough" to stop search.
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* Larger values make compression stronger, and slower.
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* For strategy fast:
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* Distance between match sampling.
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* Larger values make compression faster, and weaker.
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* Special: value 0 means "use default targetLength". */
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ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b>
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* The higher the value of selected strategy, the more complex it is,
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* resulting in stronger and slower compression.
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* Special: value 0 means "use default strategy". */
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</b>/* LDM mode parameters */<b>
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ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b>
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* This parameter is designed to improve compression ratio
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* for large inputs, by finding large matches at long distance.
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* It increases memory usage and window size.
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* Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB
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* except when expressly set to a different value. */
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ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b>
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* Larger values increase memory usage and compression ratio,
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* but decrease compression speed.
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* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX
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* default: windowlog - 7.
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* Special: value 0 means "automatically determine hashlog". */
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ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b>
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* Larger/too small values usually decrease compression ratio.
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* Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX.
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* Special: value 0 means "use default value" (default: 64). */
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ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b>
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* Larger values improve collision resolution but decrease compression speed.
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* The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX.
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* Special: value 0 means "use default value" (default: 3). */
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ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b>
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* Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN).
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* Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage.
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* Larger values improve compression speed.
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* Deviating far from default value will likely result in a compression ratio decrease.
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* Special: value 0 means "automatically determine hashRateLog". */
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</b>/* frame parameters */<b>
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ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b>
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* Content size must be known at the beginning of compression.
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* This is automatically the case when using ZSTD_compress2(),
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* For streaming variants, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */
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ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b>
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ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b>
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</b>/* multi-threading parameters */<b>
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</b>/* These parameters are only useful if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b>
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* They return an error otherwise. */
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ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b>
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* When nbWorkers >= 1, triggers asynchronous mode when used with ZSTD_compressStream*() :
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* ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller,
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* while compression work is performed in parallel, within worker threads.
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* (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end :
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* in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call).
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* More workers improve speed, but also increase memory usage.
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* Default value is `0`, aka "single-threaded mode" : no worker is spawned, compression is performed inside Caller's thread, all invocations are blocking */
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ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b>
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* Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads.
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* 0 means default, which is dynamically determined based on compression parameters.
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* Job size must be a minimum of overlap size, or 1 MB, whichever is largest.
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* The minimum size is automatically and transparently enforced */
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ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b>
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* The overlap size is an amount of data reloaded from previous job at the beginning of a new job.
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* It helps preserve compression ratio, while each job is compressed in parallel.
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* This value is enforced only when nbWorkers >= 1.
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* Larger values increase compression ratio, but decrease speed.
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* Possible values range from 0 to 9 :
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* - 0 means "default" : value will be determined by the library, depending on strategy
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* - 1 means "no overlap"
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* - 9 means "full overlap", using a full window size.
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* Each intermediate rank increases/decreases load size by a factor 2 :
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* 9: full window; 8: w/2; 7: w/4; 6: w/8; 5:w/16; 4: w/32; 3:w/64; 2:w/128; 1:no overlap; 0:default
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* default value varies between 6 and 9, depending on strategy */
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</b>/* note : additional experimental parameters are also available<b>
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* within the experimental section of the API.
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* At the time of this writing, they include :
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* ZSTD_c_rsyncable
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* ZSTD_c_format
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* ZSTD_c_forceMaxWindow
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* ZSTD_c_forceAttachDict
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* ZSTD_c_literalCompressionMode
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* ZSTD_c_targetCBlockSize
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* ZSTD_c_srcSizeHint
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* Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
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* note : never ever use experimentalParam? names directly;
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* also, the enums values themselves are unstable and can still change.
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*/
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ZSTD_c_experimentalParam1=500,
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ZSTD_c_experimentalParam2=10,
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ZSTD_c_experimentalParam3=1000,
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ZSTD_c_experimentalParam4=1001,
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ZSTD_c_experimentalParam5=1002,
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ZSTD_c_experimentalParam6=1003,
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ZSTD_c_experimentalParam7=1004,
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} ZSTD_cParameter;
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</b></pre><BR>
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<pre><b>typedef struct {
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size_t error;
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int lowerBound;
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int upperBound;
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} ZSTD_bounds;
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</b></pre><BR>
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<pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam);
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</b><p> All parameters must belong to an interval with lower and upper bounds,
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otherwise they will either trigger an error or be automatically clamped.
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@return : a structure, ZSTD_bounds, which contains
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- an error status field, which must be tested using ZSTD_isError()
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- lower and upper bounds, both inclusive
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</p></pre><BR>
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<pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value);
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</b><p> Set one compression parameter, selected by enum ZSTD_cParameter.
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All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds().
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|
Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
|
|
Setting a parameter is generally only possible during frame initialization (before starting compression).
|
|
Exception : when using multi-threading mode (nbWorkers >= 1),
|
|
the following parameters can be updated _during_ compression (within same frame):
|
|
=> compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy.
|
|
new parameters will be active for next job only (after a flush()).
|
|
@return : an error code (which can be tested using ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize);
|
|
</b><p> Total input data size to be compressed as a single frame.
|
|
Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag.
|
|
This value will also be controlled at end of frame, and trigger an error if not respected.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame.
|
|
In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN.
|
|
ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame.
|
|
Note 2 : pledgedSrcSize is only valid once, for the next frame.
|
|
It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN.
|
|
Note 3 : Whenever all input data is provided and consumed in a single round,
|
|
for example with ZSTD_compress2(),
|
|
or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end),
|
|
this value is automatically overridden by srcSize instead.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>typedef enum {
|
|
ZSTD_reset_session_only = 1,
|
|
ZSTD_reset_parameters = 2,
|
|
ZSTD_reset_session_and_parameters = 3
|
|
} ZSTD_ResetDirective;
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset);
|
|
</b><p> There are 2 different things that can be reset, independently or jointly :
|
|
- The session : will stop compressing current frame, and make CCtx ready to start a new one.
|
|
Useful after an error, or to interrupt any ongoing compression.
|
|
Any internal data not yet flushed is cancelled.
|
|
Compression parameters and dictionary remain unchanged.
|
|
They will be used to compress next frame.
|
|
Resetting session never fails.
|
|
- The parameters : changes all parameters back to "default".
|
|
This removes any reference to any dictionary too.
|
|
Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing)
|
|
otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError())
|
|
- Both : similar to resetting the session, followed by resetting parameters.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize);
|
|
</b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API.
|
|
ZSTD_compress2() always starts a new frame.
|
|
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*()
|
|
- The function is always blocking, returns when compression is completed.
|
|
Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
|
|
@return : compressed size written into `dst` (<= `dstCapacity),
|
|
or an error code if it fails (which can be tested using ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter6"></a><h2>Advanced decompression API</h2><pre></pre>
|
|
|
|
<pre><b>typedef enum {
|
|
|
|
ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b>
|
|
* the streaming API will refuse to allocate memory buffer
|
|
* in order to protect the host from unreasonable memory requirements.
|
|
* This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
|
|
* By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT).
|
|
* Special: value 0 means "use default maximum windowLog". */
|
|
|
|
</b>/* note : additional experimental parameters are also available<b>
|
|
* within the experimental section of the API.
|
|
* At the time of this writing, they include :
|
|
* ZSTD_c_format
|
|
* Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
|
|
* note : never ever use experimentalParam? names directly
|
|
*/
|
|
ZSTD_d_experimentalParam1=1000
|
|
|
|
} ZSTD_dParameter;
|
|
</b></pre><BR>
|
|
<pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam);
|
|
</b><p> All parameters must belong to an interval with lower and upper bounds,
|
|
otherwise they will either trigger an error or be automatically clamped.
|
|
@return : a structure, ZSTD_bounds, which contains
|
|
- an error status field, which must be tested using ZSTD_isError()
|
|
- both lower and upper bounds, inclusive
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value);
|
|
</b><p> Set one compression parameter, selected by enum ZSTD_dParameter.
|
|
All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds().
|
|
Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
|
|
Setting a parameter is only possible during frame initialization (before starting decompression).
|
|
@return : 0, or an error code (which can be tested using ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset);
|
|
</b><p> Return a DCtx to clean state.
|
|
Session and parameters can be reset jointly or separately.
|
|
Parameters can only be reset when no active frame is being decompressed.
|
|
@return : 0, or an error code, which can be tested with ZSTD_isError()
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter7"></a><h2>Streaming</h2><pre></pre>
|
|
|
|
<pre><b>typedef struct ZSTD_inBuffer_s {
|
|
const void* src; </b>/**< start of input buffer */<b>
|
|
size_t size; </b>/**< size of input buffer */<b>
|
|
size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
|
|
} ZSTD_inBuffer;
|
|
</b></pre><BR>
|
|
<pre><b>typedef struct ZSTD_outBuffer_s {
|
|
void* dst; </b>/**< start of output buffer */<b>
|
|
size_t size; </b>/**< size of output buffer */<b>
|
|
size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
|
|
} ZSTD_outBuffer;
|
|
</b></pre><BR>
|
|
<a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre>
|
|
A ZSTD_CStream object is required to track streaming operation.
|
|
Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
|
|
ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
|
|
It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory.
|
|
|
|
For parallel execution, use one separate ZSTD_CStream per thread.
|
|
|
|
note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing.
|
|
|
|
Parameters are sticky : when starting a new compression on the same context,
|
|
it will re-use the same sticky parameters as previous compression session.
|
|
When in doubt, it's recommended to fully initialize the context before usage.
|
|
Use ZSTD_CCtx_reset() to reset the context and ZSTD_CCtx_setParameter(),
|
|
ZSTD_CCtx_setPledgedSrcSize(), or ZSTD_CCtx_loadDictionary() and friends to
|
|
set more specific parameters, the pledged source size, or load a dictionary.
|
|
|
|
Use ZSTD_compressStream2() with ZSTD_e_continue as many times as necessary to
|
|
consume input stream. The function will automatically update both `pos`
|
|
fields within `input` and `output`.
|
|
Note that the function may not consume the entire input, for example, because
|
|
the output buffer is already full, in which case `input.pos < input.size`.
|
|
The caller must check if input has been entirely consumed.
|
|
If not, the caller must make some room to receive more compressed data,
|
|
and then present again remaining input data.
|
|
note: ZSTD_e_continue is guaranteed to make some forward progress when called,
|
|
but doesn't guarantee maximal forward progress. This is especially relevant
|
|
when compressing with multiple threads. The call won't block if it can
|
|
consume some input, but if it can't it will wait for some, but not all,
|
|
output to be flushed.
|
|
@return : provides a minimum amount of data remaining to be flushed from internal buffers
|
|
or an error code, which can be tested using ZSTD_isError().
|
|
|
|
At any moment, it's possible to flush whatever data might remain stuck within internal buffer,
|
|
using ZSTD_compressStream2() with ZSTD_e_flush. `output->pos` will be updated.
|
|
Note that, if `output->size` is too small, a single invocation with ZSTD_e_flush might not be enough (return code > 0).
|
|
In which case, make some room to receive more compressed data, and call again ZSTD_compressStream2() with ZSTD_e_flush.
|
|
You must continue calling ZSTD_compressStream2() with ZSTD_e_flush until it returns 0, at which point you can change the
|
|
operation.
|
|
note: ZSTD_e_flush will flush as much output as possible, meaning when compressing with multiple threads, it will
|
|
block until the flush is complete or the output buffer is full.
|
|
@return : 0 if internal buffers are entirely flushed,
|
|
>0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
|
|
or an error code, which can be tested using ZSTD_isError().
|
|
|
|
Calling ZSTD_compressStream2() with ZSTD_e_end instructs to finish a frame.
|
|
It will perform a flush and write frame epilogue.
|
|
The epilogue is required for decoders to consider a frame completed.
|
|
flush operation is the same, and follows same rules as calling ZSTD_compressStream2() with ZSTD_e_flush.
|
|
You must continue calling ZSTD_compressStream2() with ZSTD_e_end until it returns 0, at which point you are free to
|
|
start a new frame.
|
|
note: ZSTD_e_end will flush as much output as possible, meaning when compressing with multiple threads, it will
|
|
block until the flush is complete or the output buffer is full.
|
|
@return : 0 if frame fully completed and fully flushed,
|
|
>0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
|
|
or an error code, which can be tested using ZSTD_isError().
|
|
|
|
|
|
<BR></pre>
|
|
|
|
<pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b>
|
|
</b></pre><BR>
|
|
<h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
|
|
size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
|
|
</pre></b><BR>
|
|
<h3>Streaming compression functions</h3><pre></pre><b><pre>typedef enum {
|
|
ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b>
|
|
ZSTD_e_flush=1, </b>/* flush any data provided so far,<b>
|
|
* it creates (at least) one new block, that can be decoded immediately on reception;
|
|
* frame will continue: any future data can still reference previously compressed data, improving compression.
|
|
* note : multithreaded compression will block to flush as much output as possible. */
|
|
ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b>
|
|
* note that frame is only closed after compressed data is fully flushed (return value == 0).
|
|
* After that point, any additional data starts a new frame.
|
|
* note : each frame is independent (does not reference any content from previous frame).
|
|
: note : multithreaded compression will block to flush as much output as possible. */
|
|
} ZSTD_EndDirective;
|
|
</pre></b><BR>
|
|
<pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx,
|
|
ZSTD_outBuffer* output,
|
|
ZSTD_inBuffer* input,
|
|
ZSTD_EndDirective endOp);
|
|
</b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive.
|
|
- Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
|
|
- Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode)
|
|
- output->pos must be <= dstCapacity, input->pos must be <= srcSize
|
|
- output->pos and input->pos will be updated. They are guaranteed to remain below their respective limit.
|
|
- When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller.
|
|
- When nbWorkers>=1, function is non-blocking : it just acquires a copy of input, and distributes jobs to internal worker threads, flush whatever is available,
|
|
and then immediately returns, just indicating that there is some data remaining to be flushed.
|
|
The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte.
|
|
- Exception : if the first call requests a ZSTD_e_end directive and provides enough dstCapacity, the function delegates to ZSTD_compress2() which is always blocking.
|
|
- @return provides a minimum amount of data remaining to be flushed from internal buffers
|
|
or an error code, which can be tested using ZSTD_isError().
|
|
if @return != 0, flush is not fully completed, there is still some data left within internal buffers.
|
|
This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers.
|
|
For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed.
|
|
- after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0),
|
|
only ZSTD_e_end or ZSTD_e_flush operations are allowed.
|
|
Before starting a new compression job, or changing compression parameters,
|
|
it is required to fully flush internal buffers.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block. */<b>
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
|
|
</b>/*!<b>
|
|
* Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue).
|
|
* NOTE: The return value is different. ZSTD_compressStream() returns a hint for
|
|
* the next read size (if non-zero and not an error). ZSTD_compressStream2()
|
|
* returns the minimum nb of bytes left to flush (if non-zero and not an error).
|
|
*/
|
|
size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
|
|
</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush). */<b>
|
|
size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
|
|
</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end). */<b>
|
|
size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
|
|
</b><p>
|
|
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any)
|
|
ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre>
|
|
A ZSTD_DStream object is required to track streaming operations.
|
|
Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
|
|
ZSTD_DStream objects can be re-used multiple times.
|
|
|
|
Use ZSTD_initDStream() to start a new decompression operation.
|
|
@return : recommended first input size
|
|
Alternatively, use advanced API to set specific properties.
|
|
|
|
Use ZSTD_decompressStream() repetitively to consume your input.
|
|
The function will update both `pos` fields.
|
|
If `input.pos < input.size`, some input has not been consumed.
|
|
It's up to the caller to present again remaining data.
|
|
The function tries to flush all data decoded immediately, respecting output buffer size.
|
|
If `output.pos < output.size`, decoder has flushed everything it could.
|
|
But if `output.pos == output.size`, there might be some data left within internal buffers.,
|
|
In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer.
|
|
Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX.
|
|
@return : 0 when a frame is completely decoded and fully flushed,
|
|
or an error code, which can be tested using ZSTD_isError(),
|
|
or any other value > 0, which means there is still some decoding or flushing to do to complete current frame :
|
|
the return value is a suggested next input size (just a hint for better latency)
|
|
that will never request more than the remaining frame size.
|
|
|
|
<BR></pre>
|
|
|
|
<pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b>
|
|
</b></pre><BR>
|
|
<h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
|
|
size_t ZSTD_freeDStream(ZSTD_DStream* zds);
|
|
</pre></b><BR>
|
|
<h3>Streaming decompression functions</h3><pre></pre><b><pre></pre></b><BR>
|
|
<pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_DStreamOutSize(void); </b>/*!< recommended size for output buffer. Guarantee to successfully flush at least one complete block in all circumstances. */<b>
|
|
</b></pre><BR>
|
|
<a name="Chapter10"></a><h2>Simple dictionary API</h2><pre></pre>
|
|
|
|
<pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const void* dict,size_t dictSize,
|
|
int compressionLevel);
|
|
</b><p> Compression at an explicit compression level using a Dictionary.
|
|
A dictionary can be any arbitrary data segment (also called a prefix),
|
|
or a buffer with specified information (see dictBuilder/zdict.h).
|
|
Note : This function loads the dictionary, resulting in significant startup delay.
|
|
It's intended for a dictionary used only once.
|
|
Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const void* dict,size_t dictSize);
|
|
</b><p> Decompression using a known Dictionary.
|
|
Dictionary must be identical to the one used during compression.
|
|
Note : This function loads the dictionary, resulting in significant startup delay.
|
|
It's intended for a dictionary used only once.
|
|
Note : When `dict == NULL || dictSize < 8` no dictionary is used.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter11"></a><h2>Bulk processing dictionary API</h2><pre></pre>
|
|
|
|
<pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize,
|
|
int compressionLevel);
|
|
</b><p> When compressing multiple messages / blocks using the same dictionary, it's recommended to load it only once.
|
|
ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup cost.
|
|
ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
|
|
`dictBuffer` can be released after ZSTD_CDict creation, because its content is copied within CDict.
|
|
Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate `dictBuffer` content.
|
|
Note : A ZSTD_CDict can be created from an empty dictBuffer, but it is inefficient when used to compress small data.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
|
|
</b><p> Function frees memory allocated by ZSTD_createCDict().
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const ZSTD_CDict* cdict);
|
|
</b><p> Compression using a digested Dictionary.
|
|
Recommended when same dictionary is used multiple times.
|
|
Note : compression level is _decided at dictionary creation time_,
|
|
and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
|
|
</b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
|
|
dictBuffer can be released after DDict creation, as its content is copied inside DDict.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
|
|
</b><p> Function frees memory allocated with ZSTD_createDDict()
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const ZSTD_DDict* ddict);
|
|
</b><p> Decompression using a digested Dictionary.
|
|
Recommended when same dictionary is used multiple times.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter12"></a><h2>Dictionary helper functions</h2><pre></pre>
|
|
|
|
<pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
|
|
</b><p> Provides the dictID stored within dictionary.
|
|
if @return == 0, the dictionary is not conformant with Zstandard specification.
|
|
It can still be loaded, but as a content-only dictionary.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
|
|
</b><p> Provides the dictID of the dictionary loaded into `ddict`.
|
|
If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
|
|
Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
|
|
</b><p> Provides the dictID required to decompressed the frame stored within `src`.
|
|
If @return == 0, the dictID could not be decoded.
|
|
This could for one of the following reasons :
|
|
- The frame does not require a dictionary to be decoded (most common case).
|
|
- The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
|
|
Note : this use case also happens when using a non-conformant dictionary.
|
|
- `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
|
|
- This is not a Zstandard frame.
|
|
When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter13"></a><h2>Advanced dictionary and prefix API</h2><pre>
|
|
This API allows dictionaries to be used with ZSTD_compress2(),
|
|
ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and
|
|
only reset with the context is reset with ZSTD_reset_parameters or
|
|
ZSTD_reset_session_and_parameters. Prefixes are single-use.
|
|
<BR></pre>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
|
|
</b><p> Create an internal CDict from `dict` buffer.
|
|
Decompression will have to use same dictionary.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary,
|
|
meaning "return to no-dictionary mode".
|
|
Note 1 : Dictionary is sticky, it will be used for all future compressed frames.
|
|
To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters).
|
|
Note 2 : Loading a dictionary involves building tables.
|
|
It's also a CPU consuming operation, with non-negligible impact on latency.
|
|
Tables are dependent on compression parameters, and for this reason,
|
|
compression parameters can no longer be changed after loading a dictionary.
|
|
Note 3 :`dict` content will be copied internally.
|
|
Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead.
|
|
In such a case, dictionary buffer must outlive its users.
|
|
Note 4 : Use ZSTD_CCtx_loadDictionary_advanced()
|
|
to precisely select how dictionary content must be interpreted.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
|
|
</b><p> Reference a prepared dictionary, to be used for all next compressed frames.
|
|
Note that compression parameters are enforced from within CDict,
|
|
and supersede any compression parameter previously set within CCtx.
|
|
The parameters ignored are labled as "superseded-by-cdict" in the ZSTD_cParameter enum docs.
|
|
The ignored parameters will be used again if the CCtx is returned to no-dictionary mode.
|
|
The dictionary will remain valid for future compressed frames using same CCtx.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special : Referencing a NULL CDict means "return to no-dictionary mode".
|
|
Note 1 : Currently, only one dictionary can be managed.
|
|
Referencing a new dictionary effectively "discards" any previous one.
|
|
Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
|
|
const void* prefix, size_t prefixSize);
|
|
</b><p> Reference a prefix (single-usage dictionary) for next compressed frame.
|
|
A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end).
|
|
Decompression will need same prefix to properly regenerate data.
|
|
Compressing with a prefix is similar in outcome as performing a diff and compressing it,
|
|
but performs much faster, especially during decompression (compression speed is tunable with compression level).
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary
|
|
Note 1 : Prefix buffer is referenced. It **must** outlive compression.
|
|
Its content must remain unmodified during compression.
|
|
Note 2 : If the intention is to diff some large src data blob with some prior version of itself,
|
|
ensure that the window size is large enough to contain the entire source.
|
|
See ZSTD_c_windowLog.
|
|
Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters.
|
|
It's a CPU consuming operation, with non-negligible impact on latency.
|
|
If there is a need to use the same prefix multiple times, consider loadDictionary instead.
|
|
Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dm_rawContent).
|
|
Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
|
|
</b><p> Create an internal DDict from dict buffer,
|
|
to be used to decompress next frames.
|
|
The dictionary remains valid for all future frames, until explicitly invalidated.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary,
|
|
meaning "return to no-dictionary mode".
|
|
Note 1 : Loading a dictionary involves building tables,
|
|
which has a non-negligible impact on CPU usage and latency.
|
|
It's recommended to "load once, use many times", to amortize the cost
|
|
Note 2 :`dict` content will be copied internally, so `dict` can be released after loading.
|
|
Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead.
|
|
Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of
|
|
how dictionary content is loaded and interpreted.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
|
|
</b><p> Reference a prepared dictionary, to be used to decompress next frames.
|
|
The dictionary remains active for decompression of future frames using same DCtx.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Note 1 : Currently, only one dictionary can be managed.
|
|
Referencing a new dictionary effectively "discards" any previous one.
|
|
Special: referencing a NULL DDict means "return to no-dictionary mode".
|
|
Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx,
|
|
const void* prefix, size_t prefixSize);
|
|
</b><p> Reference a prefix (single-usage dictionary) to decompress next frame.
|
|
This is the reverse operation of ZSTD_CCtx_refPrefix(),
|
|
and must use the same prefix as the one used during compression.
|
|
Prefix is **only used once**. Reference is discarded at end of frame.
|
|
End of frame is reached when ZSTD_decompressStream() returns 0.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary
|
|
Note 2 : Prefix buffer is referenced. It **must** outlive decompression.
|
|
Prefix buffer must remain unmodified up to the end of frame,
|
|
reached when ZSTD_decompressStream() returns 0.
|
|
Note 3 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent).
|
|
Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section)
|
|
Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost.
|
|
A full dictionary is more costly, as it requires building tables.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
|
|
size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
|
|
size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
|
|
size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
|
|
size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
|
|
size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
|
|
</b><p> These functions give the _current_ memory usage of selected object.
|
|
Note that object memory usage can evolve (increase or decrease) over time.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter14"></a><h2>experimental API (static linking only)</h2><pre>
|
|
The following symbols and constants
|
|
are not planned to join "stable API" status in the near future.
|
|
They can still change in future versions.
|
|
Some of them are planned to remain in the static_only section indefinitely.
|
|
Some of them might be removed in the future (especially when redundant with existing stable functions)
|
|
|
|
<BR></pre>
|
|
|
|
<pre><b>typedef struct {
|
|
unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
|
|
unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
|
|
unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
|
|
unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
|
|
unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
|
|
unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
|
|
ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b>
|
|
} ZSTD_compressionParameters;
|
|
</b></pre><BR>
|
|
<pre><b>typedef struct {
|
|
int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b>
|
|
int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b>
|
|
int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b>
|
|
} ZSTD_frameParameters;
|
|
</b></pre><BR>
|
|
<pre><b>typedef struct {
|
|
ZSTD_compressionParameters cParams;
|
|
ZSTD_frameParameters fParams;
|
|
} ZSTD_parameters;
|
|
</b></pre><BR>
|
|
<pre><b>typedef enum {
|
|
ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b>
|
|
ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b>
|
|
ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b>
|
|
} ZSTD_dictContentType_e;
|
|
</b></pre><BR>
|
|
<pre><b>typedef enum {
|
|
ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b>
|
|
ZSTD_dlm_byRef = 1, </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b>
|
|
} ZSTD_dictLoadMethod_e;
|
|
</b></pre><BR>
|
|
<pre><b>typedef enum {
|
|
</b>/* Opened question : should we have a format ZSTD_f_auto ?<b>
|
|
* Today, it would mean exactly the same as ZSTD_f_zstd1.
|
|
* But, in the future, should several formats become supported,
|
|
* on the compression side, it would mean "default format".
|
|
* On the decompression side, it would mean "automatic format detection",
|
|
* so that ZSTD_f_zstd1 would mean "accept *only* zstd frames".
|
|
* Since meaning is a little different, another option could be to define different enums for compression and decompression.
|
|
* This question could be kept for later, when there are actually multiple formats to support,
|
|
* but there is also the question of pinning enum values, and pinning value `0` is especially important */
|
|
ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b>
|
|
ZSTD_f_zstd1_magicless = 1, </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b>
|
|
* Useful to save 4 bytes per generated frame.
|
|
* Decoder cannot recognise automatically this format, requiring this instruction. */
|
|
} ZSTD_format_e;
|
|
</b></pre><BR>
|
|
<pre><b>typedef enum {
|
|
</b>/* Note: this enum and the behavior it controls are effectively internal<b>
|
|
* implementation details of the compressor. They are expected to continue
|
|
* to evolve and should be considered only in the context of extremely
|
|
* advanced performance tuning.
|
|
*
|
|
* Zstd currently supports the use of a CDict in two ways:
|
|
*
|
|
* - The contents of the CDict can be copied into the working context. This
|
|
* means that the compression can search both the dictionary and input
|
|
* while operating on a single set of internal tables. This makes
|
|
* the compression faster per-byte of input. However, the initial copy of
|
|
* the CDict's tables incurs a fixed cost at the beginning of the
|
|
* compression. For small compressions (< 8 KB), that copy can dominate
|
|
* the cost of the compression.
|
|
*
|
|
* - The CDict's tables can be used in-place. In this model, compression is
|
|
* slower per input byte, because the compressor has to search two sets of
|
|
* tables. However, this model incurs no start-up cost (as long as the
|
|
* working context's tables can be reused). For small inputs, this can be
|
|
* faster than copying the CDict's tables.
|
|
*
|
|
* Zstd has a simple internal heuristic that selects which strategy to use
|
|
* at the beginning of a compression. However, if experimentation shows that
|
|
* Zstd is making poor choices, it is possible to override that choice with
|
|
* this enum.
|
|
*/
|
|
ZSTD_dictDefaultAttach = 0, </b>/* Use the default heuristic. */<b>
|
|
ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b>
|
|
ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b>
|
|
} ZSTD_dictAttachPref_e;
|
|
</b></pre><BR>
|
|
<pre><b>typedef enum {
|
|
ZSTD_lcm_auto = 0, </b>/**< Automatically determine the compression mode based on the compression level.<b>
|
|
* Negative compression levels will be uncompressed, and positive compression
|
|
* levels will be compressed. */
|
|
ZSTD_lcm_huffman = 1, </b>/**< Always attempt Huffman compression. Uncompressed literals will still be<b>
|
|
* emitted if Huffman compression is not profitable. */
|
|
ZSTD_lcm_uncompressed = 2, </b>/**< Always emit uncompressed literals. */<b>
|
|
} ZSTD_literalCompressionMode_e;
|
|
</b></pre><BR>
|
|
<a name="Chapter15"></a><h2>Frame size functions</h2><pre></pre>
|
|
|
|
<pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
|
|
</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames
|
|
`srcSize` must be the _exact_ size of this series
|
|
(i.e. there should be a frame boundary at `src + srcSize`)
|
|
@return : - decompressed size of all data in all successive frames
|
|
- if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
|
|
- if an error occurred: ZSTD_CONTENTSIZE_ERROR
|
|
|
|
note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
|
|
When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
|
|
In which case, it's necessary to use streaming mode to decompress data.
|
|
note 2 : decompressed size is always present when compression is done with ZSTD_compress()
|
|
note 3 : decompressed size can be very large (64-bits value),
|
|
potentially larger than what local system can handle as a single memory segment.
|
|
In which case, it's necessary to use streaming mode to decompress data.
|
|
note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
|
|
Always ensure result fits within application's authorized limits.
|
|
Each application can set its own limits.
|
|
note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
|
|
read each contained frame header. This is fast as most of the data is skipped,
|
|
however it does mean that all frame data must be present and valid.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize);
|
|
</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames
|
|
`srcSize` must be the _exact_ size of this series
|
|
(i.e. there should be a frame boundary at `src + srcSize`)
|
|
@return : - upper-bound for the decompressed size of all data in all successive frames
|
|
- if an error occured: ZSTD_CONTENTSIZE_ERROR
|
|
|
|
note 1 : an error can occur if `src` contains an invalid or incorrectly formatted frame.
|
|
note 2 : the upper-bound is exact when the decompressed size field is available in every ZSTD encoded frame of `src`.
|
|
in this case, `ZSTD_findDecompressedSize` and `ZSTD_decompressBound` return the same value.
|
|
note 3 : when the decompressed size field isn't available, the upper-bound for that frame is calculated by:
|
|
upper-bound = # blocks * min(128 KB, Window_Size)
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
|
|
</b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX.
|
|
@return : size of the Frame Header,
|
|
or an error code (if srcSize is too small)
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter16"></a><h2>Memory management</h2><pre></pre>
|
|
|
|
<pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel);
|
|
size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
|
|
size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);
|
|
size_t ZSTD_estimateDCtxSize(void);
|
|
</b><p> 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.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel);
|
|
size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams);
|
|
size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params);
|
|
size_t ZSTD_estimateDStreamSize(size_t windowSize);
|
|
size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize);
|
|
</b><p> ZSTD_estimateCStreamSize() 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_estimateCStreamSize_usingCParams() can provide a tighter estimation.
|
|
ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
|
|
ZSTD_estimateCStreamSize_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 : CStream size estimation is only correct for single-threaded compression.
|
|
ZSTD_DStream memory budget depends on window Size.
|
|
This information can be passed manually, using ZSTD_estimateDStreamSize,
|
|
or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame();
|
|
Note : if streaming is init with function ZSTD_init?Stream_usingDict(),
|
|
an internal ?Dict will be created, which additional size is not estimated here.
|
|
In this case, get total size by adding ZSTD_estimate?DictSize
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel);
|
|
size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod);
|
|
size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod);
|
|
</b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict().
|
|
ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced().
|
|
Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
|
|
ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b>
|
|
</b><p> Initialize an object using a pre-allocated fixed-size buffer.
|
|
workspace: The memory area to emplace the object into.
|
|
Provided pointer *must be 8-bytes aligned*.
|
|
Buffer must outlive object.
|
|
workspaceSize: Use ZSTD_estimate*Size() to determine
|
|
how large workspace must be to support target scenario.
|
|
@return : pointer to object (same address as workspace, just different type),
|
|
or NULL if error (size too small, incorrect alignment, etc.)
|
|
Note : zstd will never resize nor malloc() when using a static buffer.
|
|
If the object requires more memory than available,
|
|
zstd will just error out (typically ZSTD_error_memory_allocation).
|
|
Note 2 : there is no corresponding "free" function.
|
|
Since workspace is allocated externally, it must be freed externally too.
|
|
Note 3 : cParams : use ZSTD_getCParams() to convert a compression level
|
|
into its associated cParams.
|
|
Limitation 1 : currently not compatible with internal dictionary creation, triggered by
|
|
ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict().
|
|
Limitation 2 : static cctx currently not compatible with multi-threading.
|
|
Limitation 3 : static dctx is incompatible with legacy support.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b>
|
|
</b></pre><BR>
|
|
<pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
|
|
typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
|
|
typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
|
|
static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b>
|
|
</b><p> These prototypes make it possible to pass your own allocation/free functions.
|
|
ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below.
|
|
All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones.
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter17"></a><h2>Advanced compression functions</h2><pre></pre>
|
|
|
|
<pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
|
|
</b><p> Create a digested dictionary for compression
|
|
Dictionary content is just referenced, not duplicated.
|
|
As a consequence, `dictBuffer` **must** outlive CDict,
|
|
and its content must remain unmodified throughout the lifetime of CDict.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
|
|
</b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
|
|
`estimatedSrcSize` value is optional, select 0 if not known
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
|
|
</b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
|
|
All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
|
|
</b><p> Ensure param values remain within authorized range.
|
|
@return 0 on success, or an error code (can be checked with ZSTD_isError())
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
|
|
</b><p> optimize params for a given `srcSize` and `dictSize`.
|
|
`srcSize` can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN.
|
|
`dictSize` must be `0` when there is no dictionary.
|
|
cPar can be invalid : all parameters will be clamped within valid range in the @return struct.
|
|
This function never fails (wide contract)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const void* dict,size_t dictSize,
|
|
ZSTD_parameters params);
|
|
</b><p> Same as ZSTD_compress_usingDict(), with fine-tune control over compression parameters (by structure)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const ZSTD_CDict* cdict,
|
|
ZSTD_frameParameters fParams);
|
|
</b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
|
|
</b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx.
|
|
It saves some memory, but also requires that `dict` outlives its usage within `cctx`
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_loadDictionary_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod, ZSTD_dictContentType_e dictContentType);
|
|
</b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over
|
|
how to load the dictionary (by copy ? by reference ?)
|
|
and how to interpret it (automatic ? force raw mode ? full mode only ?)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
|
|
</b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over
|
|
how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_getParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value);
|
|
</b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter,
|
|
and store it into int* value.
|
|
@return : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void);
|
|
size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params);
|
|
</b><p> Quick howto :
|
|
- ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure
|
|
- ZSTD_CCtxParams_setParameter() : Push parameters one by one into
|
|
an existing ZSTD_CCtx_params structure.
|
|
This is similar to
|
|
ZSTD_CCtx_setParameter().
|
|
- ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to
|
|
an existing CCtx.
|
|
These parameters will be applied to
|
|
all subsequent frames.
|
|
- ZSTD_compressStream2() : Do compression using the CCtx.
|
|
- ZSTD_freeCCtxParams() : Free the memory.
|
|
|
|
This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams()
|
|
for static allocation of CCtx for single-threaded compression.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params);
|
|
</b><p> Reset params to default values.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel);
|
|
</b><p> Initializes the compression parameters of cctxParams according to
|
|
compression level. All other parameters are reset to their default values.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params);
|
|
</b><p> Initializes the compression and frame parameters of cctxParams according to
|
|
params. All other parameters are reset to their default values.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtxParams_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value);
|
|
</b><p> Similar to ZSTD_CCtx_setParameter.
|
|
Set one compression parameter, selected by enum ZSTD_cParameter.
|
|
Parameters must be applied to a ZSTD_CCtx using ZSTD_CCtx_setParametersUsingCCtxParams().
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtxParams_getParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value);
|
|
</b><p> Similar to ZSTD_CCtx_getParameter.
|
|
Get the requested value of one compression parameter, selected by enum ZSTD_cParameter.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams(
|
|
ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params);
|
|
</b><p> Apply a set of ZSTD_CCtx_params to the compression context.
|
|
This can be done even after compression is started,
|
|
if nbWorkers==0, this will have no impact until a new compression is started.
|
|
if nbWorkers>=1, new parameters will be picked up at next job,
|
|
with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compressStream2_simpleArgs (
|
|
ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity, size_t* dstPos,
|
|
const void* src, size_t srcSize, size_t* srcPos,
|
|
ZSTD_EndDirective endOp);
|
|
</b><p> Same as ZSTD_compressStream2(),
|
|
but using only integral types as arguments.
|
|
This variant might be helpful for binders from dynamic languages
|
|
which have troubles handling structures containing memory pointers.
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter18"></a><h2>Advanced decompression functions</h2><pre></pre>
|
|
|
|
<pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
|
|
</b><p> Tells if the content of `buffer` starts with a valid Frame Identifier.
|
|
Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
|
|
Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
|
|
Note 3 : Skippable Frame Identifiers are considered valid.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
|
|
</b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
|
|
Dictionary content is referenced, and therefore stays in dictBuffer.
|
|
It is important that dictBuffer outlives DDict,
|
|
it must remain read accessible throughout the lifetime of DDict
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
|
|
</b><p> Same as ZSTD_DCtx_loadDictionary(),
|
|
but references `dict` content instead of copying it into `dctx`.
|
|
This saves memory if `dict` remains around.,
|
|
However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_loadDictionary_advanced(ZSTD_DCtx* dctx, const void* dict, size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod, ZSTD_dictContentType_e dictContentType);
|
|
</b><p> Same as ZSTD_DCtx_loadDictionary(),
|
|
but gives direct control over
|
|
how to load the dictionary (by copy ? by reference ?)
|
|
and how to interpret it (automatic ? force raw mode ? full mode only ?).
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
|
|
</b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over
|
|
how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize);
|
|
</b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit.
|
|
This protects a decoder context from reserving too much memory for itself (potential attack scenario).
|
|
This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
|
|
By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT)
|
|
@return : 0, or an error code (which can be tested using ZSTD_isError()).
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format);
|
|
</b><p> Instruct the decoder context about what kind of data to decode next.
|
|
This instruction is mandatory to decode data without a fully-formed header,
|
|
such ZSTD_f_zstd1_magicless for example.
|
|
@return : 0, or an error code (which can be tested using ZSTD_isError()).
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_decompressStream_simpleArgs (
|
|
ZSTD_DCtx* dctx,
|
|
void* dst, size_t dstCapacity, size_t* dstPos,
|
|
const void* src, size_t srcSize, size_t* srcPos);
|
|
</b><p> Same as ZSTD_decompressStream(),
|
|
but using only integral types as arguments.
|
|
This can be helpful for binders from dynamic languages
|
|
which have troubles handling structures containing memory pointers.
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter19"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API.
|
|
Once Advanced API reaches "stable" status,
|
|
redundant functions will be deprecated, and then at some point removed.
|
|
<BR></pre>
|
|
|
|
<h3>Advanced Streaming compression functions</h3><pre></pre><b><pre></b>/**! ZSTD_initCStream_srcSize() :<b>
|
|
* This function is deprecated, and equivalent to:
|
|
* ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
* ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any)
|
|
* ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
|
|
* ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
|
|
*
|
|
* pledgedSrcSize must be correct. If it is not known at init time, use
|
|
* ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs,
|
|
* "0" also disables frame content size field. It may be enabled in the future.
|
|
*/
|
|
size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);
|
|
</b>/**! ZSTD_initCStream_usingDict() :<b>
|
|
* This function is deprecated, and is equivalent to:
|
|
* ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
* ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
|
|
* ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
|
|
*
|
|
* Creates of an internal CDict (incompatible with static CCtx), except if
|
|
* dict == NULL or dictSize < 8, in which case no dict is used.
|
|
* Note: dict is loaded with ZSTD_dm_auto (treated as a full zstd dictionary if
|
|
* it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy.
|
|
*/
|
|
size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel);
|
|
</b>/**! ZSTD_initCStream_advanced() :<b>
|
|
* This function is deprecated, and is approximately equivalent to:
|
|
* ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
* // Pseudocode: Set each zstd parameter and leave the rest as-is.
|
|
* for ((param, value) : params) {
|
|
* ZSTD_CCtx_setParameter(zcs, param, value);
|
|
* }
|
|
* ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
|
|
* ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
|
|
*
|
|
* pledgedSrcSize must be correct. If srcSize is not known at init time, use
|
|
* value ZSTD_CONTENTSIZE_UNKNOWN. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy.
|
|
*/
|
|
size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
|
|
ZSTD_parameters params, unsigned long long pledgedSrcSize);
|
|
</b>/**! ZSTD_initCStream_usingCDict() :<b>
|
|
* This function is deprecated, and equivalent to:
|
|
* ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
* ZSTD_CCtx_refCDict(zcs, cdict);
|
|
*
|
|
* note : cdict will just be referenced, and must outlive compression session
|
|
*/
|
|
size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);
|
|
</b>/**! ZSTD_initCStream_usingCDict_advanced() :<b>
|
|
* This function is deprecated, and is approximately equivalent to:
|
|
* ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
* // Pseudocode: Set each zstd frame parameter and leave the rest as-is.
|
|
* for ((fParam, value) : fParams) {
|
|
* ZSTD_CCtx_setParameter(zcs, fParam, value);
|
|
* }
|
|
* ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
|
|
* ZSTD_CCtx_refCDict(zcs, cdict);
|
|
*
|
|
* same as ZSTD_initCStream_usingCDict(), with control over frame parameters.
|
|
* pledgedSrcSize must be correct. If srcSize is not known at init time, use
|
|
* value ZSTD_CONTENTSIZE_UNKNOWN.
|
|
*/
|
|
size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize);
|
|
</pre></b><BR>
|
|
<pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
|
|
</b><p> This function is deprecated, and is equivalent to:
|
|
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
|
|
ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
|
|
|
|
start a new frame, using same parameters from previous frame.
|
|
This is typically useful to skip dictionary loading stage, since it will re-use it in-place.
|
|
Note that zcs must be init at least once before using ZSTD_resetCStream().
|
|
If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN.
|
|
If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
|
|
For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs,
|
|
but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead.
|
|
@return : 0, or an error code (which can be tested using ZSTD_isError())
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>typedef struct {
|
|
unsigned long long ingested; </b>/* nb input bytes read and buffered */<b>
|
|
unsigned long long consumed; </b>/* nb input bytes actually compressed */<b>
|
|
unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b>
|
|
unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b>
|
|
unsigned currentJobID; </b>/* MT only : latest started job nb */<b>
|
|
unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b>
|
|
} ZSTD_frameProgression;
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx);
|
|
</b><p> Tell how many bytes are ready to be flushed immediately.
|
|
Useful for multithreading scenarios (nbWorkers >= 1).
|
|
Probe the oldest active job, defined as oldest job not yet entirely flushed,
|
|
and check its output buffer.
|
|
@return : amount of data stored in oldest job and ready to be flushed immediately.
|
|
if @return == 0, it means either :
|
|
+ there is no active job (could be checked with ZSTD_frameProgression()), or
|
|
+ oldest job is still actively compressing data,
|
|
but everything it has produced has also been flushed so far,
|
|
therefore flush speed is limited by production speed of oldest job
|
|
irrespective of the speed of concurrent (and newer) jobs.
|
|
|
|
</p></pre><BR>
|
|
|
|
<h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre></b>/**<b>
|
|
* This function is deprecated, and is equivalent to:
|
|
*
|
|
* ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
|
|
* ZSTD_DCtx_loadDictionary(zds, dict, dictSize);
|
|
*
|
|
* note: no dictionary will be used if dict == NULL or dictSize < 8
|
|
*/
|
|
size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize);
|
|
</b>/**<b>
|
|
* This function is deprecated, and is equivalent to:
|
|
*
|
|
* ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
|
|
* ZSTD_DCtx_refDDict(zds, ddict);
|
|
*
|
|
* note : ddict is referenced, it must outlive decompression session
|
|
*/
|
|
size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict);
|
|
</b>/**<b>
|
|
* This function is deprecated, and is equivalent to:
|
|
*
|
|
* ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
|
|
*
|
|
* re-use decompression parameters from previous init; saves dictionary loading
|
|
*/
|
|
size_t ZSTD_resetDStream(ZSTD_DStream* zds);
|
|
</pre></b><BR>
|
|
<a name="Chapter20"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
|
|
This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
|
|
But it's also a complex one, with several restrictions, documented below.
|
|
Prefer normal streaming API for an easier experience.
|
|
|
|
<BR></pre>
|
|
|
|
<a name="Chapter21"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
|
|
A ZSTD_CCtx object is required to track streaming operations.
|
|
Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
|
|
ZSTD_CCtx object can be re-used multiple times within successive compression operations.
|
|
|
|
Start by initializing a context.
|
|
Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
|
|
or ZSTD_compressBegin_advanced(), for finer parameter control.
|
|
It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
|
|
|
|
Then, consume your input using ZSTD_compressContinue().
|
|
There are some important considerations to keep in mind when using this advanced function :
|
|
- ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only.
|
|
- Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks.
|
|
- Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
|
|
Worst case evaluation is provided by ZSTD_compressBound().
|
|
ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
|
|
- ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
|
|
It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
|
|
- ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
|
|
In which case, it will "discard" the relevant memory section from its history.
|
|
|
|
Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
|
|
It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame.
|
|
Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders.
|
|
|
|
`ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again.
|
|
<BR></pre>
|
|
|
|
<h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
|
|
size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
|
|
size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize : If srcSize is not known at init time, use ZSTD_CONTENTSIZE_UNKNOWN */<b>
|
|
size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b>
|
|
size_t ZSTD_compressBegin_usingCDict_advanced(ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict, ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize); </b>/* compression parameters are already set within cdict. pledgedSrcSize must be correct. If srcSize is not known, use macro ZSTD_CONTENTSIZE_UNKNOWN */<b>
|
|
size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize is not known, use ZSTD_CONTENTSIZE_UNKNOWN */<b>
|
|
</pre></b><BR>
|
|
<a name="Chapter22"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
|
|
A ZSTD_DCtx object is required to track streaming operations.
|
|
Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
|
|
A ZSTD_DCtx object can be re-used multiple times.
|
|
|
|
First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader().
|
|
Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough.
|
|
Data fragment must be large enough to ensure successful decoding.
|
|
`ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough.
|
|
@result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled.
|
|
>0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
|
|
errorCode, which can be tested using ZSTD_isError().
|
|
|
|
It fills a ZSTD_frameHeader structure with important information to correctly decode the frame,
|
|
such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`).
|
|
Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information.
|
|
As a consequence, check that values remain within valid application range.
|
|
For example, do not allocate memory blindly, check that `windowSize` is within expectation.
|
|
Each application can set its own limits, depending on local restrictions.
|
|
For extended interoperability, it is recommended to support `windowSize` of at least 8 MB.
|
|
|
|
ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes.
|
|
ZSTD_decompressContinue() is very sensitive to contiguity,
|
|
if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
|
|
or that previous contiguous segment is large enough to properly handle maximum back-reference distance.
|
|
There are multiple ways to guarantee this condition.
|
|
|
|
The most memory efficient way is to use a round buffer of sufficient size.
|
|
Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(),
|
|
which can @return an error code if required value is too large for current system (in 32-bits mode).
|
|
In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one,
|
|
up to the moment there is not enough room left in the buffer to guarantee decoding another full block,
|
|
which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`.
|
|
At which point, decoding can resume from the beginning of the buffer.
|
|
Note that already decoded data stored in the buffer should be flushed before being overwritten.
|
|
|
|
There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory.
|
|
|
|
Finally, if you control the compression process, you can also ignore all buffer size rules,
|
|
as long as the encoder and decoder progress in "lock-step",
|
|
aka use exactly the same buffer sizes, break contiguity at the same place, etc.
|
|
|
|
Once buffers are setup, start decompression, with ZSTD_decompressBegin().
|
|
If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict().
|
|
|
|
Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
|
|
ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
|
|
ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
|
|
|
|
@result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
|
|
It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item.
|
|
It can also be an error code, which can be tested with ZSTD_isError().
|
|
|
|
A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
|
|
Context can then be reset to start a new decompression.
|
|
|
|
Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
|
|
This information is not required to properly decode a frame.
|
|
|
|
== Special case : skippable frames
|
|
|
|
Skippable frames allow integration of user-defined data into a flow of concatenated frames.
|
|
Skippable frames will be ignored (skipped) by decompressor.
|
|
The format of skippable frames is as follows :
|
|
a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
|
|
b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
|
|
c) Frame Content - any content (User Data) of length equal to Frame Size
|
|
For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame.
|
|
For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content.
|
|
<BR></pre>
|
|
|
|
<h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e;
|
|
typedef struct {
|
|
unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b>
|
|
unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b>
|
|
unsigned blockSizeMax;
|
|
ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b>
|
|
unsigned headerSize;
|
|
unsigned dictID;
|
|
unsigned checksumFlag;
|
|
} ZSTD_frameHeader;
|
|
</pre></b><BR>
|
|
<pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b>
|
|
</b>/*! ZSTD_getFrameHeader_advanced() :<b>
|
|
* same as ZSTD_getFrameHeader(),
|
|
* with added capability to select a format (like ZSTD_f_zstd1_magicless) */
|
|
size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format);
|
|
size_t ZSTD_decodingBufferSize_min(unsigned long long windowSize, unsigned long long frameContentSize); </b>/**< when frame content size is not known, pass in frameContentSize == ZSTD_CONTENTSIZE_UNKNOWN */<b>
|
|
</b><p> decode Frame Header, or requires larger `srcSize`.
|
|
@return : 0, `zfhPtr` is correctly filled,
|
|
>0, `srcSize` is too small, value is wanted `srcSize` amount,
|
|
or an error code, which can be tested using ZSTD_isError()
|
|
</p></pre><BR>
|
|
|
|
<pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
|
|
</b></pre><BR>
|
|
<a name="Chapter23"></a><h2>Block level API</h2><pre></pre>
|
|
|
|
<pre><b></b><p> Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes).
|
|
But users will have to take in charge needed metadata to regenerate data, such as compressed and content sizes.
|
|
|
|
A few rules to respect :
|
|
- Compressing and decompressing require a context structure
|
|
+ Use ZSTD_createCCtx() and ZSTD_createDCtx()
|
|
- It is necessary to init context before starting
|
|
+ compression : any ZSTD_compressBegin*() variant, including with dictionary
|
|
+ decompression : any ZSTD_decompressBegin*() variant, including with dictionary
|
|
+ copyCCtx() and copyDCtx() can be used too
|
|
- Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB
|
|
+ If input is larger than a block size, it's necessary to split input data into multiple blocks
|
|
+ For inputs larger than a single block, consider using regular ZSTD_compress() instead.
|
|
Frame metadata is not that costly, and quickly becomes negligible as source size grows larger than a block.
|
|
- When a block is considered not compressible enough, ZSTD_compressBlock() result will be 0 (zero) !
|
|
===> In which case, nothing is produced into `dst` !
|
|
+ User __must__ test for such outcome and deal directly with uncompressed data
|
|
+ A block cannot be declared incompressible if ZSTD_compressBlock() return value was != 0.
|
|
Doing so would mess up with statistics history, leading to potential data corruption.
|
|
+ ZSTD_decompressBlock() _doesn't accept uncompressed data as input_ !!
|
|
+ In case of multiple successive blocks, should some of them be uncompressed,
|
|
decoder must be informed of their existence in order to follow proper history.
|
|
Use ZSTD_insertBlock() for such a case.
|
|
</p></pre><BR>
|
|
|
|
<h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx);
|
|
size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
|
|
size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
|
|
size_t ZSTD_insertBlock (ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize); </b>/**< insert uncompressed block into `dctx` history. Useful for multi-blocks decompression. */<b>
|
|
</pre></b><BR>
|
|
</html>
|
|
</body>
|