459 lines
24 KiB
HTML
459 lines
24 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>1.8.3 Manual</title>
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</head>
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<body>
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<h1>1.8.3 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">Tuning parameter</a></li>
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<li><a href="#Chapter4">Simple Functions</a></li>
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<li><a href="#Chapter5">Advanced Functions</a></li>
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<li><a href="#Chapter6">Streaming Compression Functions</a></li>
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<li><a href="#Chapter7">Streaming Decompression Functions</a></li>
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<li><a href="#Chapter8">Unstable declarations</a></li>
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<li><a href="#Chapter9">PRIVATE DEFINITIONS</a></li>
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<li><a href="#Chapter10">Obsolete Functions</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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LZ4 is lossless compression algorithm, providing compression speed at 500 MB/s per core,
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scalable with multi-cores CPU. It features an extremely fast decoder, with speed in
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multiple GB/s per core, typically reaching RAM speed limits on multi-core systems.
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The LZ4 compression library provides in-memory compression and decompression functions.
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Compression can be done in:
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- a single step (described as Simple Functions)
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- a single step, reusing a context (described in Advanced Functions)
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- unbounded multiple steps (described as Streaming compression)
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lz4.h provides block compression functions. It gives full buffer control to user.
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Decompressing an lz4-compressed block also requires metadata (such as compressed size).
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Each application is free to encode such metadata in whichever way it wants.
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An additional format, called LZ4 frame specification (doc/lz4_Frame_format.md),
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take care of encoding standard metadata alongside LZ4-compressed blocks.
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Frame format is required for interoperability.
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It is delivered through a companion API, declared in lz4frame.h.
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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>int LZ4_versionNumber (void); </b>/**< library version number; useful to check dll version */<b>
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</b></pre><BR>
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<pre><b>const char* LZ4_versionString (void); </b>/**< library version string; useful to check dll version */<b>
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</b></pre><BR>
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<a name="Chapter3"></a><h2>Tuning parameter</h2><pre></pre>
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<pre><b>#ifndef LZ4_MEMORY_USAGE
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# define LZ4_MEMORY_USAGE 14
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#endif
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</b><p> Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
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Increasing memory usage improves compression ratio.
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Reduced memory usage may improve speed, thanks to better cache locality.
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Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache
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</p></pre><BR>
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<a name="Chapter4"></a><h2>Simple Functions</h2><pre></pre>
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<pre><b>int LZ4_compress_default(const char* src, char* dst, int srcSize, int dstCapacity);
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</b><p> Compresses 'srcSize' bytes from buffer 'src'
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into already allocated 'dst' buffer of size 'dstCapacity'.
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Compression is guaranteed to succeed if 'dstCapacity' >= LZ4_compressBound(srcSize).
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It also runs faster, so it's a recommended setting.
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If the function cannot compress 'src' into a more limited 'dst' budget,
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compression stops *immediately*, and the function result is zero.
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In which case, 'dst' content is undefined (invalid).
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srcSize : max supported value is LZ4_MAX_INPUT_SIZE.
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dstCapacity : size of buffer 'dst' (which must be already allocated)
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@return : the number of bytes written into buffer 'dst' (necessarily <= dstCapacity)
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or 0 if compression fails
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Note : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer).
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</p></pre><BR>
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<pre><b>int LZ4_decompress_safe (const char* src, char* dst, int compressedSize, int dstCapacity);
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</b><p> compressedSize : is the exact complete size of the compressed block.
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dstCapacity : is the size of destination buffer, which must be already allocated.
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@return : the number of bytes decompressed into destination buffer (necessarily <= dstCapacity)
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If destination buffer is not large enough, decoding will stop and output an error code (negative value).
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If the source stream is detected malformed, the function will stop decoding and return a negative result.
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Note : This function is protected against malicious data packets (never writes outside 'dst' buffer, nor read outside 'source' buffer).
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</p></pre><BR>
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<a name="Chapter5"></a><h2>Advanced Functions</h2><pre></pre>
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<pre><b>int LZ4_compressBound(int inputSize);
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</b><p> Provides the maximum size that LZ4 compression may output in a "worst case" scenario (input data not compressible)
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This function is primarily useful for memory allocation purposes (destination buffer size).
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Macro LZ4_COMPRESSBOUND() is also provided for compilation-time evaluation (stack memory allocation for example).
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Note that LZ4_compress_default() compresses faster when dstCapacity is >= LZ4_compressBound(srcSize)
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inputSize : max supported value is LZ4_MAX_INPUT_SIZE
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return : maximum output size in a "worst case" scenario
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or 0, if input size is incorrect (too large or negative)
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</p></pre><BR>
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<pre><b>int LZ4_compress_fast (const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
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</b><p> Same as LZ4_compress_default(), but allows selection of "acceleration" factor.
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The larger the acceleration value, the faster the algorithm, but also the lesser the compression.
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It's a trade-off. It can be fine tuned, with each successive value providing roughly +~3% to speed.
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An acceleration value of "1" is the same as regular LZ4_compress_default()
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Values <= 0 will be replaced by ACCELERATION_DEFAULT (currently == 1, see lz4.c).
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</p></pre><BR>
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<pre><b>int LZ4_sizeofState(void);
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int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
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</b><p> Same as LZ4_compress_fast(), using an externally allocated memory space for its state.
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Use LZ4_sizeofState() to know how much memory must be allocated,
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and allocate it on 8-bytes boundaries (using `malloc()` typically).
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Then, provide this buffer as `void* state` to compression function.
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</p></pre><BR>
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<pre><b>int LZ4_compress_destSize (const char* src, char* dst, int* srcSizePtr, int targetDstSize);
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</b><p> Reverse the logic : compresses as much data as possible from 'src' buffer
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into already allocated buffer 'dst', of size >= 'targetDestSize'.
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This function either compresses the entire 'src' content into 'dst' if it's large enough,
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or fill 'dst' buffer completely with as much data as possible from 'src'.
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note: acceleration parameter is fixed to "default".
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*srcSizePtr : will be modified to indicate how many bytes where read from 'src' to fill 'dst'.
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New value is necessarily <= input value.
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@return : Nb bytes written into 'dst' (necessarily <= targetDestSize)
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or 0 if compression fails.
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</p></pre><BR>
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<pre><b>int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
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</b><p> This function used to be a bit faster than LZ4_decompress_safe(),
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though situation has changed in recent versions,
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and now `LZ4_decompress_safe()` can be as fast and sometimes faster than `LZ4_decompress_fast()`.
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Moreover, LZ4_decompress_fast() is not protected vs malformed input, as it doesn't perform full validation of compressed data.
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As a consequence, this function is no longer recommended, and may be deprecated in future versions.
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It's last remaining specificity is that it can decompress data without knowing its compressed size.
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originalSize : is the uncompressed size to regenerate.
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`dst` must be already allocated, its size must be >= 'originalSize' bytes.
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@return : number of bytes read from source buffer (== compressed size).
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If the source stream is detected malformed, the function stops decoding and returns a negative result.
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note : This function requires uncompressed originalSize to be known in advance.
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The function never writes past the output buffer.
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However, since it doesn't know its 'src' size, it may read past the intended input.
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Also, because match offsets are not validated during decoding,
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reads from 'src' may underflow.
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Use this function in trusted environment **only**.
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</p></pre><BR>
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<pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity);
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</b><p> Decompress an LZ4 compressed block, of size 'srcSize' at position 'src',
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into destination buffer 'dst' of size 'dstCapacity'.
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Up to 'targetOutputSize' bytes will be decoded.
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The function stops decoding on reaching this objective,
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which can boost performance when only the beginning of a block is required.
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@return : the number of bytes decoded in `dst` (necessarily <= dstCapacity)
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If source stream is detected malformed, function returns a negative result.
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Note : @return can be < targetOutputSize, if compressed block contains less data.
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Note 2 : this function features 2 parameters, targetOutputSize and dstCapacity,
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and expects targetOutputSize <= dstCapacity.
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It effectively stops decoding on reaching targetOutputSize,
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so dstCapacity is kind of redundant.
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This is because in a previous version of this function,
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decoding operation would not "break" a sequence in the middle.
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As a consequence, there was no guarantee that decoding would stop at exactly targetOutputSize,
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it could write more bytes, though only up to dstCapacity.
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Some "margin" used to be required for this operation to work properly.
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This is no longer necessary.
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The function nonetheless keeps its signature, in an effort to not break API.
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</p></pre><BR>
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<a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre>
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<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr);
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</b><p> An LZ4_stream_t structure can be allocated once and re-used multiple times.
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Use this function to start compressing a new stream.
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</p></pre><BR>
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<pre><b>int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize);
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</b><p> Use this function to load a static dictionary into LZ4_stream_t.
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Any previous data will be forgotten, only 'dictionary' will remain in memory.
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Loading a size of 0 is allowed, and is the same as reset.
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@return : dictionary size, in bytes (necessarily <= 64 KB)
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</p></pre><BR>
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<pre><b>int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
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</b><p> Compress 'src' content using data from previously compressed blocks, for better compression ratio.
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'dst' buffer must be already allocated.
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If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster.
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@return : size of compressed block
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or 0 if there is an error (typically, cannot fit into 'dst').
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Note 1 : Each invocation to LZ4_compress_fast_continue() generates a new block.
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Each block has precise boundaries.
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Each block must be decompressed separately, calling LZ4_decompress_*() with relevant metadata.
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It's not possible to append blocks together and expect a single invocation of LZ4_decompress_*() to decompress them together.
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Note 2 : The previous 64KB of source data is __assumed__ to remain present, unmodified, at same address in memory !
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Note 3 : When input is structured as a double-buffer, each buffer can have any size, including < 64 KB.
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Make sure that buffers are separated, by at least one byte.
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This construction ensures that each block only depends on previous block.
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Note 4 : If input buffer is a ring-buffer, it can have any size, including < 64 KB.
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Note 5 : After an error, the stream status is undefined (invalid), it can only be reset or freed.
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</p></pre><BR>
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<pre><b>int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int maxDictSize);
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</b><p> If last 64KB data cannot be guaranteed to remain available at its current memory location,
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save it into a safer place (char* safeBuffer).
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This is schematically equivalent to a memcpy() followed by LZ4_loadDict(),
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but is much faster, because LZ4_saveDict() doesn't need to rebuild tables.
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@return : saved dictionary size in bytes (necessarily <= maxDictSize), or 0 if error.
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</p></pre><BR>
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<a name="Chapter7"></a><h2>Streaming Decompression Functions</h2><pre> Bufferless synchronous API
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<BR></pre>
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<pre><b>LZ4_streamDecode_t* LZ4_createStreamDecode(void);
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int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
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</b><p> creation / destruction of streaming decompression tracking context.
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A tracking context can be re-used multiple times.
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</p></pre><BR>
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<pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize);
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</b><p> An LZ4_streamDecode_t context can be allocated once and re-used multiple times.
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Use this function to start decompression of a new stream of blocks.
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A dictionary can optionally be set. Use NULL or size 0 for a reset order.
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Dictionary is presumed stable : it must remain accessible and unmodified during next decompression.
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@return : 1 if OK, 0 if error
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</p></pre><BR>
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<pre><b>int LZ4_decoderRingBufferSize(int maxBlockSize);
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#define LZ4_DECODER_RING_BUFFER_SIZE(maxBlockSize) (65536 + 14 + (maxBlockSize)) </b>/* for static allocation; maxBlockSize presumed valid */<b>
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</b><p> Note : in a ring buffer scenario (optional),
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blocks are presumed decompressed next to each other
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up to the moment there is not enough remaining space for next block (remainingSize < maxBlockSize),
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at which stage it resumes from beginning of ring buffer.
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When setting such a ring buffer for streaming decompression,
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provides the minimum size of this ring buffer
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to be compatible with any source respecting maxBlockSize condition.
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@return : minimum ring buffer size,
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or 0 if there is an error (invalid maxBlockSize).
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</p></pre><BR>
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<pre><b>int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int srcSize, int dstCapacity);
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int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize);
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</b><p> These decoding functions allow decompression of consecutive blocks in "streaming" mode.
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A block is an unsplittable entity, it must be presented entirely to a decompression function.
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Decompression functions only accepts one block at a time.
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The last 64KB of previously decoded data *must* remain available and unmodified at the memory position where they were decoded.
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If less than 64KB of data has been decoded, all the data must be present.
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Special : if decompression side sets a ring buffer, it must respect one of the following conditions :
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- Decompression buffer size is _at least_ LZ4_decoderRingBufferSize(maxBlockSize).
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maxBlockSize is the maximum size of any single block. It can have any value > 16 bytes.
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In which case, encoding and decoding buffers do not need to be synchronized.
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Actually, data can be produced by any source compliant with LZ4 format specification, and respecting maxBlockSize.
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- Synchronized mode :
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Decompression buffer size is _exactly_ the same as compression buffer size,
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and follows exactly same update rule (block boundaries at same positions),
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and decoding function is provided with exact decompressed size of each block (exception for last block of the stream),
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_then_ decoding & encoding ring buffer can have any size, including small ones ( < 64 KB).
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- Decompression buffer is larger than encoding buffer, by a minimum of maxBlockSize more bytes.
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In which case, encoding and decoding buffers do not need to be synchronized,
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and encoding ring buffer can have any size, including small ones ( < 64 KB).
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Whenever these conditions are not possible,
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save the last 64KB of decoded data into a safe buffer where it can't be modified during decompression,
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then indicate where this data is saved using LZ4_setStreamDecode(), before decompressing next block.
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</p></pre><BR>
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<pre><b>int LZ4_decompress_safe_usingDict (const char* src, char* dst, int srcSize, int dstCapcity, const char* dictStart, int dictSize);
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int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize);
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</b><p> These decoding functions work the same as
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a combination of LZ4_setStreamDecode() followed by LZ4_decompress_*_continue()
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They are stand-alone, and don't need an LZ4_streamDecode_t structure.
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Dictionary is presumed stable : it must remain accessible and unmodified during decompression.
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Performance tip : Decompression speed can be substantially increased
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when dst == dictStart + dictSize.
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</p></pre><BR>
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<a name="Chapter8"></a><h2>Unstable declarations</h2><pre>
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Declarations in this section must be considered unstable.
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Their signatures may change, or may be removed in the future.
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They are therefore only safe to depend on
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when the caller is statically linked against the library.
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To access their declarations, define LZ4_STATIC_LINKING_ONLY.
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<BR></pre>
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<pre><b>LZ4LIB_STATIC_API void LZ4_resetStream_fast (LZ4_stream_t* streamPtr);
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</b><p> Use this to prepare a context for a new chain of calls to a streaming API
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(e.g., LZ4_compress_fast_continue()).
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Note:
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To stay on the safe side, when LZ4_stream_t is used for the first time,
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it should be either created using LZ4_createStream() or
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initialized using LZ4_resetStream().
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Note:
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Using this in advance of a non-streaming-compression function is redundant,
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since they all perform their own custom reset internally.
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Differences from LZ4_resetStream():
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When an LZ4_stream_t is known to be in an internally coherent state,
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it will be prepared for a new compression with almost no work.
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Otherwise, it will fall back to the full, expensive reset.
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LZ4_streams are guaranteed to be in a valid state when:
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- returned from LZ4_createStream()
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- reset by LZ4_resetStream()
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- memset(stream, 0, sizeof(LZ4_stream_t)), though this is discouraged
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- the stream was in a valid state and was reset by LZ4_resetStream_fast()
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- the stream was in a valid state and was then used in any compression call
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that returned success
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- the stream was in an indeterminate state and was used in a compression
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call that fully reset the state (e.g., LZ4_compress_fast_extState()) and
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that returned success
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Note:
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A stream that was used in a compression call that did not return success
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(e.g., LZ4_compress_fast_continue()), can still be passed to this function,
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however, it's history is not preserved because of previous compression
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failure.
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</p></pre><BR>
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<pre><b>LZ4LIB_STATIC_API int LZ4_compress_fast_extState_fastReset (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
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</b><p> A variant of LZ4_compress_fast_extState().
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Using this variant avoids an expensive initialization step.
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It is only safe to call if the state buffer is known to be correctly initialized already
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(see above comment on LZ4_resetStream_fast() for a definition of "correctly initialized").
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From a high level, the difference is that
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this function initializes the provided state with a call to something like LZ4_resetStream_fast()
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while LZ4_compress_fast_extState() starts with a call to LZ4_resetStream().
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</p></pre><BR>
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<pre><b>LZ4LIB_STATIC_API void LZ4_attach_dictionary(LZ4_stream_t* workingStream, const LZ4_stream_t* dictionaryStream);
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</b><p> This is an experimental API that allows
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efficient use of a static dictionary many times.
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Rather than re-loading the dictionary buffer into a working context before
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each compression, or copying a pre-loaded dictionary's LZ4_stream_t into a
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working LZ4_stream_t, this function introduces a no-copy setup mechanism,
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in which the working stream references the dictionary stream in-place.
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Several assumptions are made about the state of the dictionary stream.
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Currently, only streams which have been prepared by LZ4_loadDict() should
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be expected to work.
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Alternatively, the provided dictionaryStream may be NULL,
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in which case any existing dictionary stream is unset.
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If a dictionary is provided, it replaces any pre-existing stream history.
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The dictionary contents are the only history that can be referenced and
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logically immediately precede the data compressed in the first subsequent
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compression call.
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The dictionary will only remain attached to the working stream through the
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first compression call, at the end of which it is cleared. The dictionary
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stream (and source buffer) must remain in-place / accessible / unchanged
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through the completion of the first compression call on the stream.
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</p></pre><BR>
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<a name="Chapter9"></a><h2>PRIVATE DEFINITIONS</h2><pre>
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Do not use these definitions directly.
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They are only exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`.
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Accessing members will expose code to API and/or ABI break in future versions of the library.
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<BR></pre>
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<pre><b>typedef struct {
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const uint8_t* externalDict;
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size_t extDictSize;
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const uint8_t* prefixEnd;
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|
size_t prefixSize;
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} LZ4_streamDecode_t_internal;
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</b></pre><BR>
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<pre><b>typedef struct {
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|
const unsigned char* externalDict;
|
|
const unsigned char* prefixEnd;
|
|
size_t extDictSize;
|
|
size_t prefixSize;
|
|
} LZ4_streamDecode_t_internal;
|
|
</b></pre><BR>
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|
<pre><b>#define LZ4_STREAMSIZE_U64 ((1 << (LZ4_MEMORY_USAGE-3)) + 4 + ((sizeof(void*)==16) ? 4 : 0) </b>/*AS-400*/ )<b>
|
|
#define LZ4_STREAMSIZE (LZ4_STREAMSIZE_U64 * sizeof(unsigned long long))
|
|
union LZ4_stream_u {
|
|
unsigned long long table[LZ4_STREAMSIZE_U64];
|
|
LZ4_stream_t_internal internal_donotuse;
|
|
} ; </b>/* previously typedef'd to LZ4_stream_t */<b>
|
|
</b><p> information structure to track an LZ4 stream.
|
|
init this structure with LZ4_resetStream() before first use.
|
|
note : only use in association with static linking !
|
|
this definition is not API/ABI safe,
|
|
it may change in a future version !
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>#define LZ4_STREAMDECODESIZE_U64 (4 + ((sizeof(void*)==16) ? 2 : 0) </b>/*AS-400*/ )<b>
|
|
#define LZ4_STREAMDECODESIZE (LZ4_STREAMDECODESIZE_U64 * sizeof(unsigned long long))
|
|
union LZ4_streamDecode_u {
|
|
unsigned long long table[LZ4_STREAMDECODESIZE_U64];
|
|
LZ4_streamDecode_t_internal internal_donotuse;
|
|
} ; </b>/* previously typedef'd to LZ4_streamDecode_t */<b>
|
|
</b><p> information structure to track an LZ4 stream during decompression.
|
|
init this structure using LZ4_setStreamDecode() before first use.
|
|
note : only use in association with static linking !
|
|
this definition is not API/ABI safe,
|
|
and may change in a future version !
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter10"></a><h2>Obsolete Functions</h2><pre></pre>
|
|
|
|
<pre><b>#ifdef LZ4_DISABLE_DEPRECATE_WARNINGS
|
|
# define LZ4_DEPRECATED(message) </b>/* disable deprecation warnings */<b>
|
|
#else
|
|
# define LZ4_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
|
|
# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b>
|
|
# define LZ4_DEPRECATED(message) [[deprecated(message)]]
|
|
# elif (LZ4_GCC_VERSION >= 405) || defined(__clang__)
|
|
# define LZ4_DEPRECATED(message) __attribute__((deprecated(message)))
|
|
# elif (LZ4_GCC_VERSION >= 301)
|
|
# define LZ4_DEPRECATED(message) __attribute__((deprecated))
|
|
# elif defined(_MSC_VER)
|
|
# define LZ4_DEPRECATED(message) __declspec(deprecated(message))
|
|
# else
|
|
# pragma message("WARNING: You need to implement LZ4_DEPRECATED for this compiler")
|
|
# define LZ4_DEPRECATED(message)
|
|
# endif
|
|
#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b>
|
|
</b><p> Should deprecation warnings be a problem,
|
|
it is generally possible to disable them,
|
|
typically with -Wno-deprecated-declarations for gcc
|
|
or _CRT_SECURE_NO_WARNINGS in Visual.
|
|
Otherwise, it's also possible to define LZ4_DISABLE_DEPRECATE_WARNINGS
|
|
</p></pre><BR>
|
|
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