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| LZ4LIB_API int | LZ4_versionNumber (void) |
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| LZ4LIB_API const char * | LZ4_versionString (void) |
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| LZ4LIB_API int | LZ4_compress_default (const char *src, char *dst, int srcSize, int dstCapacity) |
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| LZ4LIB_API int | LZ4_decompress_safe (const char *src, char *dst, int compressedSize, int dstCapacity) |
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| LZ4LIB_API int | LZ4_compressBound (int inputSize) |
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| LZ4LIB_API int | LZ4_compress_fast (const char *src, char *dst, int srcSize, int dstCapacity, int acceleration) |
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| LZ4LIB_API int | LZ4_sizeofState (void) |
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| LZ4LIB_API int | LZ4_compress_fast_extState (void *state, const char *src, char *dst, int srcSize, int dstCapacity, int acceleration) |
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| LZ4LIB_API int | LZ4_compress_destSize (const char *src, char *dst, int *srcSizePtr, int targetDstSize) |
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| LZ4LIB_API int | LZ4_decompress_safe_partial (const char *src, char *dst, int srcSize, int targetOutputSize, int dstCapacity) |
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| LZ4LIB_API LZ4_stream_t * | LZ4_createStream (void) |
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| LZ4LIB_API int | LZ4_freeStream (LZ4_stream_t *streamPtr) |
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| LZ4LIB_API void | LZ4_resetStream_fast (LZ4_stream_t *streamPtr) |
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| LZ4LIB_API int | LZ4_loadDict (LZ4_stream_t *streamPtr, const char *dictionary, int dictSize) |
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| LZ4LIB_API int | LZ4_compress_fast_continue (LZ4_stream_t *streamPtr, const char *src, char *dst, int srcSize, int dstCapacity, int acceleration) |
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| LZ4LIB_API int | LZ4_saveDict (LZ4_stream_t *streamPtr, char *safeBuffer, int maxDictSize) |
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| LZ4LIB_API LZ4_streamDecode_t * | LZ4_createStreamDecode (void) |
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| LZ4LIB_API int | LZ4_freeStreamDecode (LZ4_streamDecode_t *LZ4_stream) |
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| LZ4LIB_API int | LZ4_setStreamDecode (LZ4_streamDecode_t *LZ4_streamDecode, const char *dictionary, int dictSize) |
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| LZ4LIB_API int | LZ4_decoderRingBufferSize (int maxBlockSize) |
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| LZ4LIB_API int | LZ4_decompress_safe_continue (LZ4_streamDecode_t *LZ4_streamDecode, const char *src, char *dst, int srcSize, int dstCapacity) |
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| LZ4LIB_API int | LZ4_decompress_safe_usingDict (const char *src, char *dst, int srcSize, int dstCapcity, const char *dictStart, int dictSize) |
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| LZ4LIB_API LZ4_stream_t * | LZ4_initStream (void *buffer, size_t size) |
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| | LZ4_DEPRECATED ("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress(const char *src |
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| | LZ4_DEPRECATED ("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_withState(void *state |
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| | LZ4_DEPRECATED ("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_continue(LZ4_stream_t *LZ4_streamPtr |
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| | LZ4_DEPRECATED ("use LZ4_decompress_fast() instead") LZ4LIB_API int LZ4_uncompress(const char *source |
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| | LZ4_DEPRECATED ("use LZ4_decompress_safe() instead") LZ4LIB_API int LZ4_uncompress_unknownOutputSize(const char *source |
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| | LZ4_DEPRECATED ("Use LZ4_createStream() instead") LZ4LIB_API void *LZ4_create(char *inputBuffer) |
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| | LZ4_DEPRECATED ("Use LZ4_resetStream() instead") LZ4LIB_API int LZ4_resetStreamState(void *state |
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| | LZ4_DEPRECATED ("Use LZ4_saveDict() instead") LZ4LIB_API char *LZ4_slideInputBuffer(void *state) |
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| | LZ4_DEPRECATED ("use LZ4_decompress_safe_usingDict() instead") LZ4LIB_API int LZ4_decompress_safe_withPrefix64k(const char *src |
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| | LZ4_DEPRECATED ("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4_decompress_fast_withPrefix64k(const char *src |
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| LZ4LIB_API int | LZ4_decompress_fast (const char *src, char *dst, int originalSize) |
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| LZ4LIB_API int | LZ4_decompress_fast_continue (LZ4_streamDecode_t *LZ4_streamDecode, const char *src, char *dst, int originalSize) |
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| LZ4LIB_API int | LZ4_decompress_fast_usingDict (const char *src, char *dst, int originalSize, const char *dictStart, int dictSize) |
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| LZ4LIB_API void | LZ4_resetStream (LZ4_stream_t *streamPtr) |
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| #define LZ4LIB_VISIBILITY |
Introduction
LZ4 is lossless compression algorithm, providing compression speed >500 MB/s per core, scalable with multi-cores CPU. It features an extremely fast decoder, with speed in multiple GB/s per core, typically reaching RAM speed limits on multi-core systems.
The LZ4 compression library provides in-memory compression and decompression functions. It gives full buffer control to user. Compression can be done in:
- a single step (described as Simple Functions)
- a single step, reusing a context (described in Advanced Functions)
- unbounded multiple steps (described as Streaming compression)
lz4.h generates and decodes LZ4-compressed blocks (doc/lz4_Block_format.md). Decompressing such a compressed block requires additional metadata. Exact metadata depends on exact decompression function. For the typical case of LZ4_decompress_safe(), metadata includes block's compressed size, and maximum bound of decompressed size. Each application is free to encode and pass such metadata in whichever way it wants.
lz4.h only handle blocks, it can not generate Frames.
Blocks are different from Frames (doc/lz4_Frame_format.md). Frames bundle both blocks and metadata in a specified manner. Embedding metadata is required for compressed data to be self-contained and portable. Frame format is delivered through a companion API, declared in lz4frame.h. The lz4 CLI can only manage frames.
| LZ4LIB_API int LZ4_compress_destSize |
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const char * |
src, |
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char * |
dst, |
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int * |
srcSizePtr, |
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int |
targetDstSize |
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) |
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LZ4_compress_destSize() : Reverse the logic : compresses as much data as possible from 'src' buffer into already allocated buffer 'dst', of size >= 'targetDestSize'. This function either compresses the entire 'src' content into 'dst' if it's large enough, or fill 'dst' buffer completely with as much data as possible from 'src'. note: acceleration parameter is fixed to "default".
*srcSizePtr : will be modified to indicate how many bytes where read from 'src' to fill 'dst'. New value is necessarily <= input value.
- Returns
- : Nb bytes written into 'dst' (necessarily <= targetDestSize) or 0 if compression fails.
Note : from v1.8.2 to v1.9.1, this function had a bug (fixed un v1.9.2+): the produced compressed content could, in specific circumstances, require to be decompressed into a destination buffer larger by at least 1 byte than the content to decompress. If an application uses LZ4_compress_destSize(), it's highly recommended to update liblz4 to v1.9.2 or better. If this can't be done or ensured, the receiving decompression function should provide a dstCapacity which is > decompressedSize, by at least 1 byte. See https://github.com/lz4/lz4/issues/859 for details
| LZ4LIB_API int LZ4_compress_fast_continue |
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LZ4_stream_t * |
streamPtr, |
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const char * |
src, |
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char * |
dst, |
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int |
srcSize, |
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int |
dstCapacity, |
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int |
acceleration |
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) |
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LZ4_compress_fast_continue() : Compress 'src' content using data from previously compressed blocks, for better compression ratio. 'dst' buffer must be already allocated. If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster.
- Returns
- : size of compressed block or 0 if there is an error (typically, cannot fit into 'dst').
Note 1 : Each invocation to LZ4_compress_fast_continue() generates a new block. Each block has precise boundaries. Each block must be decompressed separately, calling LZ4_decompress_*() with relevant metadata. It's not possible to append blocks together and expect a single invocation of LZ4_decompress_*() to decompress them together.
Note 2 : The previous 64KB of source data is assumed to remain present, unmodified, at same address in memory !
Note 3 : When input is structured as a double-buffer, each buffer can have any size, including < 64 KB. Make sure that buffers are separated, by at least one byte. This construction ensures that each block only depends on previous block.
Note 4 : If input buffer is a ring-buffer, it can have any size, including < 64 KB.
Note 5 : After an error, the stream status is undefined (invalid), it can only be reset or freed.
| LZ4LIB_API int LZ4_decompress_fast |
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const char * |
src, |
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char * |
dst, |
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int |
originalSize |
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) |
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Obsolete LZ4_decompress_fast variants (since v1.9.0) : 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.
- Returns
- : 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.
| LZ4LIB_API int LZ4_decompress_safe_continue |
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LZ4_streamDecode_t * |
LZ4_streamDecode, |
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const char * |
src, |
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char * |
dst, |
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int |
srcSize, |
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int |
dstCapacity |
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) |
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LZ4_decompress_*_continue() : These decoding functions allow decompression of consecutive blocks in "streaming" mode. A block is an unsplittable entity, it must be presented entirely to a decompression function. Decompression functions only accepts one block at a time. The last 64KB of previously decoded data must remain available and unmodified at the memory position where they were decoded. If less than 64KB of data has been decoded, all the data must be present.
Special : if decompression side sets a ring buffer, it must respect one of the following conditions :
- Decompression buffer size is at least LZ4_decoderRingBufferSize(maxBlockSize). maxBlockSize is the maximum size of any single block. It can have any value > 16 bytes. In which case, encoding and decoding buffers do not need to be synchronized. Actually, data can be produced by any source compliant with LZ4 format specification, and respecting maxBlockSize.
- Synchronized mode : Decompression buffer size is exactly the same as compression buffer size, and follows exactly same update rule (block boundaries at same positions), and decoding function is provided with exact decompressed size of each block (exception for last block of the stream), then decoding & encoding ring buffer can have any size, including small ones ( < 64 KB).
- Decompression buffer is larger than encoding buffer, by a minimum of maxBlockSize more bytes. In which case, encoding and decoding buffers do not need to be synchronized, and encoding ring buffer can have any size, including small ones ( < 64 KB).
Whenever these conditions are not possible, save the last 64KB of decoded data into a safe buffer where it can't be modified during decompression, then indicate where this data is saved using LZ4_setStreamDecode(), before decompressing next block.
| LZ4LIB_API int LZ4_decompress_safe_partial |
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const char * |
src, |
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char * |
dst, |
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int |
srcSize, |
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int |
targetOutputSize, |
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int |
dstCapacity |
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) |
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LZ4_decompress_safe_partial() : Decompress an LZ4 compressed block, of size 'srcSize' at position 'src', into destination buffer 'dst' of size 'dstCapacity'. Up to 'targetOutputSize' bytes will be decoded. The function stops decoding on reaching this objective. This can be useful to boost performance whenever only the beginning of a block is required.
- Returns
- : the number of bytes decoded in
dst (necessarily <= targetOutputSize) If source stream is detected malformed, function returns a negative result.
Note 1 :
- Returns
- can be < targetOutputSize, if compressed block contains less data.
Note 2 : targetOutputSize must be <= dstCapacity
Note 3 : this function effectively stops decoding on reaching targetOutputSize, so dstCapacity is kind of redundant. This is because in older versions of this function, decoding operation would still write complete sequences. Therefore, there was no guarantee that it would stop writing at exactly targetOutputSize, it could write more bytes, though only up to dstCapacity. Some "margin" used to be required for this operation to work properly. Thankfully, this is no longer necessary. The function nonetheless keeps the same signature, in an effort to preserve API compatibility.
Note 4 : If srcSize is the exact size of the block, then targetOutputSize can be any value, including larger than the block's decompressed size. The function will, at most, generate block's decompressed size.
Note 5 : If srcSize is larger than block's compressed size, then targetOutputSize MUST be <= block's decompressed size. Otherwise, silent corruption will occur.
LZ4_initStream() : v1.9.0+ 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
- Returns
- a pointer of proper type upon initialization.
Note : initialization fails if size and alignment conditions are not respected. In which case, the function will
- Returns
- NULL. Note2: An LZ4_stream_t structure guarantees correct alignment and size. Note3: Before v1.9.0, use LZ4_resetStream() instead