339 lines
17 KiB
HTML
339 lines
17 KiB
HTML
<html>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>1.8.1 Manual</title>
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</head>
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<body>
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<h1>1.8.1 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">Private definitions</a></li>
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<li><a href="#Chapter9">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 400 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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If your application requires interoperability, it's recommended to use it.
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A library is provided to take care of it, see 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; unseful 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 cache effect
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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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Note : as a consequence, 'dst' content is not valid.
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Note 2 : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer).
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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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</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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This function is protected against malicious data packets.
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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 compression function, just using an externally allocated memory space to store compression 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 it 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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*srcSizePtr : will be modified to indicate how many bytes where read from 'src' to fill 'dst'.
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New value is necessarily <= old 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 is a bit faster than LZ4_decompress_safe(),
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but doesn't provide any security guarantee.
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originalSize : is the uncompressed size to regenerate
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Destination buffer must be already allocated, and 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 return a negative result.
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note : This function respects memory boundaries for *properly formed* compressed data.
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However, it does not provide any protection against malicious input.
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It also doesn't know 'src' size, and implies it's >= compressed size.
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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> This function decompress a compressed block of size 'srcSize' at position 'src'
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into destination buffer 'dst' of size 'dstCapacity'.
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The function will decompress a minimum of 'targetOutputSize' bytes, and stop after that.
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However, it's not accurate, and may write more than 'targetOutputSize' (but always <= dstCapacity).
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@return : the number of bytes decoded in the destination buffer (necessarily <= dstCapacity)
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Note : this number can also be < targetOutputSize, if compressed block contains less data.
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Therefore, always control how many bytes were decoded.
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If source stream is detected malformed, function returns a negative result.
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This function is protected against malicious data packets.
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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>LZ4_stream_t* LZ4_createStream(void);
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int LZ4_freeStream (LZ4_stream_t* streamPtr);
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</b><p> LZ4_createStream() will allocate and initialize an `LZ4_stream_t` structure.
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LZ4_freeStream() releases its memory.
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</p></pre><BR>
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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 content into 'src' using data from previously compressed blocks, improving 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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Important : The previous 64KB of compressed data is assumed to remain preset and unmodified in memory!
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If less than 64KB has been compressed all the data must be present.
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Special 1 : If input buffer is a double-buffer, it can have any size, including < 64 KB.
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Special 2 : If input buffer is a ring-buffer, it can have any size, including < 64 KB.
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@return : size of compressed block
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or 0 if there is an error (typically, compressed data cannot fit into 'dst')
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After an error, the stream status is 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 dictSize);
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</b><p> If previously compressed data block is not 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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Note : it's not necessary to call LZ4_loadDict() after LZ4_saveDict(), dictionary is immediately usable.
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@return : saved dictionary size in bytes (necessarily <= dictSize), 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 structure.
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A tracking structure can be re-used multiple times sequentially.
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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 structure 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 optionnally be set. Use NULL or size 0 for a simple reset order.
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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_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 accept 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 application sets a ring buffer for decompression, it must respect one of the following conditions :
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- Exactly same size as encoding buffer, with same update rule (block boundaries at same positions)
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In which case, the decoding & encoding ring buffer can have any size, including very small ones ( < 64 KB).
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- Larger than encoding buffer, by a minimum of maxBlockSize more bytes.
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maxBlockSize is implementation dependent. It's the maximum size of any single block.
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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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- _At least_ 64 KB + 8 bytes + maxBlockSize.
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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 larger than decoding buffer.
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Whenever these conditions are not possible, save the last 64KB of decoded data into a safe buffer,
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and indicate where it 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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</p></pre><BR>
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<a name="Chapter8"></a><h2>Private definitions</h2><pre>
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Do not use these definitions.
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They are exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`.
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Using these definitions 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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uint32_t hashTable[LZ4_HASH_SIZE_U32];
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uint32_t currentOffset;
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uint32_t initCheck;
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const uint8_t* dictionary;
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uint8_t* bufferStart; </b>/* obsolete, used for slideInputBuffer */<b>
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uint32_t dictSize;
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} LZ4_stream_t_internal;
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</b></pre><BR>
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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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unsigned int hashTable[LZ4_HASH_SIZE_U32];
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unsigned int currentOffset;
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unsigned int initCheck;
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const unsigned char* dictionary;
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unsigned char* bufferStart; </b>/* obsolete, used for slideInputBuffer */<b>
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unsigned int dictSize;
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} LZ4_stream_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;
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size_t extDictSize;
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const unsigned char* 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>#define LZ4_STREAMSIZE_U64 ((1 << (LZ4_MEMORY_USAGE-3)) + 4)
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#define LZ4_STREAMSIZE (LZ4_STREAMSIZE_U64 * sizeof(unsigned long long))
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union LZ4_stream_u {
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unsigned long long table[LZ4_STREAMSIZE_U64];
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LZ4_stream_t_internal internal_donotuse;
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} ; </b>/* previously typedef'd to LZ4_stream_t */<b>
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</b><p> information structure to track an LZ4 stream.
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init this structure before first use.
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note : only use in association with static linking !
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this definition is not API/ABI safe,
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it may change in a future version !
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</p></pre><BR>
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<pre><b>#define LZ4_STREAMDECODESIZE_U64 4
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#define LZ4_STREAMDECODESIZE (LZ4_STREAMDECODESIZE_U64 * sizeof(unsigned long long))
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union LZ4_streamDecode_u {
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unsigned long long table[LZ4_STREAMDECODESIZE_U64];
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LZ4_streamDecode_t_internal internal_donotuse;
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} ; </b>/* previously typedef'd to LZ4_streamDecode_t */<b>
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</b><p> information structure to track an LZ4 stream during decompression.
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init this structure using LZ4_setStreamDecode (or memset()) before first use
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note : only use in association with static linking !
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this definition is not API/ABI safe,
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and may change in a future version !
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</p></pre><BR>
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<a name="Chapter9"></a><h2>Obsolete Functions</h2><pre></pre>
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<pre><b>#ifdef LZ4_DISABLE_DEPRECATE_WARNINGS
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# define LZ4_DEPRECATED(message) </b>/* disable deprecation warnings */<b>
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#else
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# define LZ4_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
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# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b>
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# define LZ4_DEPRECATED(message) [[deprecated(message)]]
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# elif (LZ4_GCC_VERSION >= 405) || defined(__clang__)
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# define LZ4_DEPRECATED(message) __attribute__((deprecated(message)))
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# elif (LZ4_GCC_VERSION >= 301)
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# define LZ4_DEPRECATED(message) __attribute__((deprecated))
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# elif defined(_MSC_VER)
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# define LZ4_DEPRECATED(message) __declspec(deprecated(message))
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# else
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# pragma message("WARNING: You need to implement LZ4_DEPRECATED for this compiler")
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# define LZ4_DEPRECATED(message)
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# endif
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#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b>
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</b><p> Should deprecation warnings be a problem,
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it is generally possible to disable them,
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typically with -Wno-deprecated-declarations for gcc
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or _CRT_SECURE_NO_WARNINGS in Visual.
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Otherwise, it's also possible to define LZ4_DISABLE_DEPRECATE_WARNINGS
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</p></pre><BR>
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</html>
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