597 lines
33 KiB
HTML
597 lines
33 KiB
HTML
<html>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>1.9.3 Manual</title>
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</head>
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<body>
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<h1>1.9.3 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">Experimental section</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 >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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It gives full buffer control to user.
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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 generates and decodes LZ4-compressed blocks (doc/lz4_Block_format.md).
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Decompressing such a compressed block requires additional metadata.
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Exact metadata depends on exact decompression function.
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For the typical case of LZ4_decompress_safe(),
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metadata includes block's compressed size, and maximum bound of decompressed size.
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Each application is free to encode and pass such metadata in whichever way it wants.
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lz4.h only handle blocks, it can not generate Frames.
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Blocks are different from Frames (doc/lz4_Frame_format.md).
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Frames bundle both blocks and metadata in a specified manner.
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Embedding metadata is required for compressed data to be self-contained and portable.
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Frame format is delivered through a companion API, declared in lz4frame.h.
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The `lz4` CLI can only manage frames.
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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), presumed an upper bound of decompressed size.
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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 1 : This function is protected against malicious data packets :
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it will never writes outside 'dst' buffer, nor read outside 'source' buffer,
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even if the compressed block is maliciously modified to order the decoder to do these actions.
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In such case, the decoder stops immediately, and considers the compressed block malformed.
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Note 2 : compressedSize and dstCapacity must be provided to the function, the compressed block does not contain them.
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The implementation is free to send / store / derive this information in whichever way is most beneficial.
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If there is a need for a different format which bundles together both compressed data and its metadata, consider looking at lz4frame.h instead.
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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 LZ4_ACCELERATION_DEFAULT (currently == 1, see lz4.c).
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Values > LZ4_ACCELERATION_MAX will be replaced by LZ4_ACCELERATION_MAX (currently == 65537, 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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Note : from v1.8.2 to v1.9.1, this function had a bug (fixed un v1.9.2+):
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the produced compressed content could, in specific circumstances,
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require to be decompressed into a destination buffer larger
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by at least 1 byte than the content to decompress.
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If an application uses `LZ4_compress_destSize()`,
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it's highly recommended to update liblz4 to v1.9.2 or better.
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If this can't be done or ensured,
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the receiving decompression function should provide
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a dstCapacity which is > decompressedSize, by at least 1 byte.
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See https://github.com/lz4/lz4/issues/859 for details
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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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This can be useful to boost performance
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whenever only the beginning of a block is required.
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@return : the number of bytes decoded in `dst` (necessarily <= targetOutputSize)
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If source stream is detected malformed, function returns a negative result.
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Note 1 : @return can be < targetOutputSize, if compressed block contains less data.
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Note 2 : targetOutputSize must be <= dstCapacity
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Note 3 : this function effectively stops decoding on reaching targetOutputSize,
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so dstCapacity is kind of redundant.
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This is because in older versions of this function,
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decoding operation would still write complete sequences.
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Therefore, there was no guarantee that it would stop writing 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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Thankfully, this is no longer necessary.
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The function nonetheless keeps the same signature, in an effort to preserve API compatibility.
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Note 4 : If srcSize is the exact size of the block,
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then targetOutputSize can be any value,
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including larger than the block's decompressed size.
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The function will, at most, generate block's decompressed size.
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Note 5 : If srcSize is _larger_ than block's compressed size,
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then targetOutputSize **MUST** be <= block's decompressed size.
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Otherwise, *silent corruption will occur*.
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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_fast (LZ4_stream_t* streamPtr);
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</b><p> Use this to prepare an LZ4_stream_t for a new chain of dependent blocks
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(e.g., LZ4_compress_fast_continue()).
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An LZ4_stream_t must be initialized once before usage.
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This is automatically done when created by LZ4_createStream().
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However, should the LZ4_stream_t be simply declared on stack (for example),
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it's necessary to initialize it first, using LZ4_initStream().
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After init, start any new stream with LZ4_resetStream_fast().
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A same LZ4_stream_t can be re-used multiple times consecutively
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and compress multiple streams,
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provided that it starts each new stream with LZ4_resetStream_fast().
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LZ4_resetStream_fast() is much faster than LZ4_initStream(),
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but is not compatible with memory regions containing garbage data.
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Note: it's only useful to call LZ4_resetStream_fast()
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in the context of streaming compression.
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The *extState* functions perform their own resets.
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Invoking LZ4_resetStream_fast() before is redundant, and even counterproductive.
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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 reference a static dictionary into LZ4_stream_t.
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The dictionary must remain available during compression.
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LZ4_loadDict() triggers a reset, so any previous data will be forgotten.
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The same dictionary will have to be loaded on decompression side for successful decoding.
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Dictionary are useful for better compression of small data (KB range).
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While LZ4 accept any input as dictionary,
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results are generally better when using Zstandard's Dictionary Builder.
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Loading a size of 0 is allowed, and is the same as reset.
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@return : loaded 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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</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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</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>Experimental section</h2><pre>
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Symbols declared in this section must be considered unstable. Their
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signatures or semantics may change, or they may be removed altogether in the
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future. They are therefore only safe to depend on when the caller is
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statically linked against the library.
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To protect against unsafe usage, not only are the declarations guarded,
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the definitions are hidden by default
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when building LZ4 as a shared/dynamic library.
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In order to access these declarations,
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define LZ4_STATIC_LINKING_ONLY in your application
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before including LZ4's headers.
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In order to make their implementations accessible dynamically, you must
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define LZ4_PUBLISH_STATIC_FUNCTIONS when building the LZ4 library.
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<BR></pre>
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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>
|
|
|
|
<pre><b></b><p>
|
|
It's possible to have input and output sharing the same buffer,
|
|
for highly contrained memory environments.
|
|
In both cases, it requires input to lay at the end of the buffer,
|
|
and decompression to start at beginning of the buffer.
|
|
Buffer size must feature some margin, hence be larger than final size.
|
|
|
|
|<------------------------buffer--------------------------------->|
|
|
|<-----------compressed data--------->|
|
|
|<-----------decompressed size------------------>|
|
|
|<----margin---->|
|
|
|
|
This technique is more useful for decompression,
|
|
since decompressed size is typically larger,
|
|
and margin is short.
|
|
|
|
In-place decompression will work inside any buffer
|
|
which size is >= LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize).
|
|
This presumes that decompressedSize > compressedSize.
|
|
Otherwise, it means compression actually expanded data,
|
|
and it would be more efficient to store such data with a flag indicating it's not compressed.
|
|
This can happen when data is not compressible (already compressed, or encrypted).
|
|
|
|
For in-place compression, margin is larger, as it must be able to cope with both
|
|
history preservation, requiring input data to remain unmodified up to LZ4_DISTANCE_MAX,
|
|
and data expansion, which can happen when input is not compressible.
|
|
As a consequence, buffer size requirements are much higher,
|
|
and memory savings offered by in-place compression are more limited.
|
|
|
|
There are ways to limit this cost for compression :
|
|
- Reduce history size, by modifying LZ4_DISTANCE_MAX.
|
|
Note that it is a compile-time constant, so all compressions will apply this limit.
|
|
Lower values will reduce compression ratio, except when input_size < LZ4_DISTANCE_MAX,
|
|
so it's a reasonable trick when inputs are known to be small.
|
|
- Require the compressor to deliver a "maximum compressed size".
|
|
This is the `dstCapacity` parameter in `LZ4_compress*()`.
|
|
When this size is < LZ4_COMPRESSBOUND(inputSize), then compression can fail,
|
|
in which case, the return code will be 0 (zero).
|
|
The caller must be ready for these cases to happen,
|
|
and typically design a backup scheme to send data uncompressed.
|
|
The combination of both techniques can significantly reduce
|
|
the amount of margin required for in-place compression.
|
|
|
|
In-place compression can work in any buffer
|
|
which size is >= (maxCompressedSize)
|
|
with maxCompressedSize == LZ4_COMPRESSBOUND(srcSize) for guaranteed compression success.
|
|
LZ4_COMPRESS_INPLACE_BUFFER_SIZE() depends on both maxCompressedSize and LZ4_DISTANCE_MAX,
|
|
so it's possible to reduce memory requirements by playing with them.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ((decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) </b>/**< note: presumes that compressedSize < decompressedSize. note2: margin is overestimated a bit, since it could use compressedSize instead */<b>
|
|
</b></pre><BR>
|
|
<pre><b>#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ((maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) </b>/**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */<b>
|
|
</b></pre><BR>
|
|
<a name="Chapter9"></a><h2>Private Definitions</h2><pre>
|
|
Do not use these definitions directly.
|
|
They are only exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`.
|
|
Accessing members will expose user code to API and/or ABI break in future versions of the library.
|
|
<BR></pre>
|
|
|
|
<pre><b>typedef struct {
|
|
const LZ4_byte* externalDict;
|
|
size_t extDictSize;
|
|
const LZ4_byte* prefixEnd;
|
|
size_t prefixSize;
|
|
} LZ4_streamDecode_t_internal;
|
|
</b></pre><BR>
|
|
<pre><b>#define LZ4_STREAMSIZE 16416 </b>/* static size, for inter-version compatibility */<b>
|
|
#define LZ4_STREAMSIZE_VOIDP (LZ4_STREAMSIZE / sizeof(void*))
|
|
union LZ4_stream_u {
|
|
void* table[LZ4_STREAMSIZE_VOIDP];
|
|
LZ4_stream_t_internal internal_donotuse;
|
|
}; </b>/* previously typedef'd to LZ4_stream_t */<b>
|
|
</b><p> Do not use below internal definitions directly !
|
|
Declare or allocate an LZ4_stream_t instead.
|
|
LZ4_stream_t can also be created using LZ4_createStream(), which is recommended.
|
|
The structure definition can be convenient for static allocation
|
|
(on stack, or as part of larger structure).
|
|
Init this structure with LZ4_initStream() before first use.
|
|
note : only use this definition in association with static linking !
|
|
this definition is not API/ABI safe, and may change in future versions.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>LZ4_stream_t* LZ4_initStream (void* buffer, size_t size);
|
|
</b><p> An LZ4_stream_t structure must be initialized at least once.
|
|
This is automatically done when invoking LZ4_createStream(),
|
|
but it's not when the structure is simply declared on stack (for example).
|
|
|
|
Use LZ4_initStream() to properly initialize a newly declared LZ4_stream_t.
|
|
It can also initialize any arbitrary buffer of sufficient size,
|
|
and will @return a pointer of proper type upon initialization.
|
|
|
|
Note : initialization fails if size and alignment conditions are not respected.
|
|
In which case, the function will @return NULL.
|
|
Note2: An LZ4_stream_t structure guarantees correct alignment and size.
|
|
Note3: Before v1.9.0, use LZ4_resetStream() instead
|
|
|
|
</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
|
|
# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b>
|
|
# define LZ4_DEPRECATED(message) [[deprecated(message)]]
|
|
# elif defined(_MSC_VER)
|
|
# define LZ4_DEPRECATED(message) __declspec(deprecated(message))
|
|
# elif defined(__clang__) || (defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 45))
|
|
# define LZ4_DEPRECATED(message) __attribute__((deprecated(message)))
|
|
# elif defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 31)
|
|
# define LZ4_DEPRECATED(message) __attribute__((deprecated))
|
|
# else
|
|
# pragma message("WARNING: LZ4_DEPRECATED needs custom implementation for this compiler")
|
|
# define LZ4_DEPRECATED(message) </b>/* disabled */<b>
|
|
# endif
|
|
#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b>
|
|
</b><p>
|
|
Deprecated functions make the compiler generate a warning when invoked.
|
|
This is meant to invite users to update their source code.
|
|
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.
|
|
|
|
Another method is to define LZ4_DISABLE_DEPRECATE_WARNINGS
|
|
before including the header file.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress (const char* src, char* dest, int srcSize);
|
|
LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress_limitedOutput (const char* src, char* dest, int srcSize, int maxOutputSize);
|
|
LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_withState (void* state, const char* source, char* dest, int inputSize);
|
|
LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_limitedOutput_withState (void* state, const char* source, char* dest, int inputSize, int maxOutputSize);
|
|
LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize);
|
|
LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_limitedOutput_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize, int maxOutputSize);
|
|
</b><p></p></pre><BR>
|
|
|
|
<pre><b>LZ4_DEPRECATED("use LZ4_decompress_fast() instead") LZ4LIB_API int LZ4_uncompress (const char* source, char* dest, int outputSize);
|
|
LZ4_DEPRECATED("use LZ4_decompress_safe() instead") LZ4LIB_API int LZ4_uncompress_unknownOutputSize (const char* source, char* dest, int isize, int maxOutputSize);
|
|
</b><p></p></pre><BR>
|
|
|
|
<pre><b>LZ4_DEPRECATED("use LZ4_decompress_safe_usingDict() instead") LZ4LIB_API int LZ4_decompress_safe_withPrefix64k (const char* src, char* dst, int compressedSize, int maxDstSize);
|
|
LZ4_DEPRECATED("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4_decompress_fast_withPrefix64k (const char* src, char* dst, int originalSize);
|
|
</b><p></p></pre><BR>
|
|
|
|
<pre><b>LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe() instead")
|
|
int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
|
|
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_continue() instead")
|
|
int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize);
|
|
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_usingDict() instead")
|
|
int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize);
|
|
</b><p> These functions used to be faster than LZ4_decompress_safe(),
|
|
but this is no longer the case. They are now slower.
|
|
This is because LZ4_decompress_fast() doesn't know the input size,
|
|
and therefore must progress more cautiously into the input buffer to not read beyond the end of block.
|
|
On top of that `LZ4_decompress_fast()` is not protected vs malformed or malicious inputs, making it a security liability.
|
|
As a consequence, LZ4_decompress_fast() is strongly discouraged, and deprecated.
|
|
|
|
The last remaining LZ4_decompress_fast() specificity is that
|
|
it can decompress a block without knowing its compressed size.
|
|
Such functionality can be achieved in a more secure manner
|
|
by employing LZ4_decompress_safe_partial().
|
|
|
|
Parameters:
|
|
originalSize : is the uncompressed size to regenerate.
|
|
`dst` must be already allocated, its size must be >= 'originalSize' bytes.
|
|
@return : number of bytes read from source buffer (== compressed size).
|
|
The function expects to finish at block's end exactly.
|
|
If the source stream is detected malformed, the function stops decoding and returns a negative result.
|
|
note : LZ4_decompress_fast*() requires originalSize. Thanks to this information, it never writes past the output buffer.
|
|
However, since it doesn't know its 'src' size, it may read an unknown amount of input, past input buffer bounds.
|
|
Also, since match offsets are not validated, match reads from 'src' may underflow too.
|
|
These issues never happen if input (compressed) data is correct.
|
|
But they may happen if input data is invalid (error or intentional tampering).
|
|
As a consequence, use these functions in trusted environments with trusted data **only**.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr);
|
|
</b><p> An LZ4_stream_t structure must be initialized at least once.
|
|
This is done with LZ4_initStream(), or LZ4_resetStream().
|
|
Consider switching to LZ4_initStream(),
|
|
invoking LZ4_resetStream() will trigger deprecation warnings in the future.
|
|
|
|
</p></pre><BR>
|
|
|
|
</html>
|
|
</body>
|