package vendor:compress/lz4

Source

• decompress_safe_continue
• freeStreamDecode
• setStreamDecode

• attach_HC_dictionary
• compress_HC_continue
• compress_HC_continue_destSize
• freeStreamHC
• loadDictHC
• resetStreamHC_fast
• saveDictHC

• attach_dictionary
• compress_fast_continue
• freeStream
• loadDict
• loadDictSlow
• resetStream_fast
• saveDict

required as macro for static allocation

2_113_929_216 bytes

static size, for inter-version compatibility

for breaking interface changes

for new (non-breaking) interface capabilities

for tweaks, bug-fixes, or development

! LZ4_attach_HC_dictionary() : stable since v1.10.0 This API allows for the efficient re-use of a static dictionary many times.

Rather than re-loading the dictionary buffer into a working context before each compression, or copying a pre-loaded dictionary's LZ4_streamHC_t into a working LZ4_streamHC_t, this function introduces a no-copy setup mechanism, in which the working stream references the dictionary stream in-place.

Several assumptions are made about the state of the dictionary stream. Currently, only streams which have been prepared by LZ4_loadDictHC() should be expected to work.

Alternatively, the provided dictionary stream pointer may be NULL, in which case any existing dictionary stream is unset.

A dictionary should only be attached to a stream without any history (i.e., a stream that has just been reset).

The dictionary will remain attached to the working stream only for the current stream session. Calls to LZ4_resetStreamHC(_fast) will remove the dictionary context association from the working stream. The dictionary stream (and source buffer) must remain in-place / accessible / unchanged through the lifetime of the stream session.

! LZ4_attach_dictionary() : stable since v1.10.0

This allows efficient re-use of a static dictionary multiple times.

Rather than re-loading the dictionary buffer into a working context before each compression, or copying a pre-loaded dictionary's LZ4_stream_t into a working LZ4_stream_t, this function introduces a no-copy setup mechanism, in which the working stream references @dictionaryStream in-place.

Several assumptions are made about the state of @dictionaryStream. Currently, only states which have been prepared by LZ4_loadDict() or LZ4_loadDictSlow() should be expected to work.

Alternatively, the provided @dictionaryStream may be NULL, in which case any existing dictionary stream is unset.

If a dictionary is provided, it replaces any pre-existing stream history. The dictionary contents are the only history that can be referenced and logically immediately precede the data compressed in the first subsequent compression call.

The dictionary will only remain attached to the working stream through the first compression call, at the end of which it is cleared. @dictionaryStream stream (and source buffer) must remain in-place / accessible / unchanged through the completion of the compression session.

Note: there is no equivalent LZ4_attach_*() method on the decompression side because there is no initialization cost, hence no need to share the cost across multiple sessions. To decompress LZ4 blocks using dictionary, attached or not, just employ the regular LZ4_setStreamDecode() for streaming, or the stateless LZ4_decompress_safe_usingDict() for one-shot decompression.

! LZ4_compressBound() :

    Provides the maximum size that LZ4 compression may output in a "worst case" scenario (input data not compressible)
    This function is primarily useful for memory allocation purposes (destination buffer size).
    Macro LZ4_COMPRESSBOUND() is also provided for compilation-time evaluation (stack memory allocation for example).
    Note that LZ4_compress_default() compresses faster when dstCapacity is >= LZ4_compressBound(srcSize)
        inputSize  : max supported value is LZ4_MAX_INPUT_SIZE
        return : maximum output size in a "worst case" scenario
              or 0, if input size is incorrect (too large or negative)

! LZ4_compress_HC() : Compress data from src into dst, using the powerful but slower "HC" algorithm. dst must be already allocated. Compression is guaranteed to succeed if dstCapacity >= LZ4_compressBound(srcSize) (see "lz4.h") Max supported srcSize value is LZ4_MAX_INPUT_SIZE (see "lz4.h") compressionLevel : any value between 1 and LZ4HC_CLEVEL_MAX will work. Values > LZ4HC_CLEVEL_MAX behave the same as LZ4HC_CLEVEL_MAX. @return : the number of bytes written into 'dst' or 0 if compression fails.

! LZ4_compress_HC_continue_destSize() : v1.9.0+ Similar to LZ4_compress_HC_continue(), but will read as much data as possible from src to fit into targetDstSize budget. Result is provided into 2 parts : @return : the number of bytes written into 'dst' (necessarily <= targetDstSize) or 0 if compression fails. srcSizePtr : on success, *srcSizePtr will be updated to indicate how much bytes were read from src. Note that this function may not consume the entire input.

! LZ4_compress_HC_destSize() : v1.9.0+ Will compress as much data as possible from src to fit into targetDstSize budget. Result is provided in 2 parts : @return : the number of bytes written into 'dst' (necessarily <= targetDstSize) or 0 if compression fails. srcSizePtr : on success, *srcSizePtr is updated to indicate how much bytes were read from src

! LZ4_compress_default() : Compresses 'srcSize' bytes from buffer 'src' into already allocated 'dst' buffer of size 'dstCapacity'. Compression is guaranteed to succeed if 'dstCapacity' >= LZ4_compressBound(srcSize). It also runs faster, so it's a recommended setting. If the function cannot compress 'src' into a more limited 'dst' budget, compression stops immediately, and the function result is zero. In which case, 'dst' content is undefined (invalid). srcSize : max supported value is LZ4_MAX_INPUT_SIZE. dstCapacity : size of buffer 'dst' (which must be already allocated) @return : the number of bytes written into buffer 'dst' (necessarily <= dstCapacity) or 0 if compression fails Note : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer).

! LZ4_compress_destSize() : Reverse the logic : compresses as much data as possible from 'src' buffer into already allocated buffer 'dst', of size >= 'dstCapacity'. 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 : in+out parameter. Initially contains size of input. Will be modified to indicate how many bytes where read from 'src' to fill 'dst'. New value is necessarily <= input value. @return : Nb bytes written into 'dst' (necessarily <= dstCapacity) or 0 if compression fails.

Note : from v1.8.2 to v1.9.1, this function had a bug (fixed in 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

! LZ4_compress_fast() :

    Same as LZ4_compress_default(), but allows selection of "acceleration" factor.
    The larger the acceleration value, the faster the algorithm, but also the lesser the compression.
    It's a trade-off. It can be fine tuned, with each successive value providing roughly +~3% to speed.
    An acceleration value of "1" is the same as regular LZ4_compress_default()
    Values <= 0 will be replaced by LZ4_ACCELERATION_DEFAULT (currently == 1, see lz4.c).
    Values > LZ4_ACCELERATION_MAX will be replaced by LZ4_ACCELERATION_MAX (currently == 65537, see lz4.c).

! 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.

@return : 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.

! LZ4_createStreamHC() and LZ4_freeStreamHC() : These functions create and release memory for LZ4 HC streaming state. Newly created states are automatically initialized. A same state can be used multiple times consecutively, starting with LZ4_resetStreamHC_fast() to start a new stream of blocks.

! LZ4_decoderRingBufferSize() : v1.8.2+ Note : in a ring buffer scenario (optional), blocks are presumed decompressed next to each other up to the moment there is not enough remaining space for next block (remainingSize < maxBlockSize), at which stage it resumes from beginning of ring buffer. When setting such a ring buffer for streaming decompression, provides the minimum size of this ring buffer to be compatible with any source respecting maxBlockSize condition. @return : minimum ring buffer size, or 0 if there is an error (invalid maxBlockSize).

! LZ4_decompress_safe() : @compressedSize : is the exact complete size of the compressed block. @dstCapacity : is the size of destination buffer (which must be already allocated), presumed an upper bound of decompressed size. @return : the number of bytes decompressed into destination buffer (necessarily <= dstCapacity) If destination buffer is not large enough, decoding will stop and output an error code (negative value). If the source stream is detected malformed, the function will stop decoding and return a negative result. Note 1 : This function is protected against malicious data packets : it will never writes outside 'dst' buffer, nor read outside 'source' buffer, even if the compressed block is maliciously modified to order the decoder to do these actions. In such case, the decoder stops immediately, and considers the compressed block malformed. Note 2 : compressedSize and dstCapacity must be provided to the function, the compressed block does not contain them. The implementation is free to send / store / derive this information in whichever way is most beneficial. If there is a need for a different format which bundles together both compressed data and its metadata, consider looking at lz4frame.h instead.

! LZ4_decompress_safe_continue() : This decoding function allows decompression of consecutive blocks in "streaming" mode. The difference with the usual independent blocks is that new blocks are allowed to find references into former blocks. A block is an unsplittable entity, and must be presented entirely to the decompression function. LZ4_decompress_safe_continue() only accepts one block at a time. It's modeled after LZ4_decompress_safe() and behaves similarly.

@LZ4_streamDecode : decompression state, tracking the position in memory of past data @compressedSize : exact complete size of one compressed block. @dstCapacity : size of destination buffer (which must be already allocated), must be an upper bound of decompressed size. @return : number of bytes decompressed into destination buffer (necessarily <= dstCapacity) If destination buffer is not large enough, decoding will stop and output an error code (negative value). If the source stream is detected malformed, the function will stop decoding and return a negative result.

The last 64KB of previously decoded data must remain available and unmodified at the memory position where they were previously 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.

! 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.

@return : the number of bytes decoded in dst (necessarily <= targetOutputSize) If source stream is detected malformed, function returns a negative result.

Note 1 : @return 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_decompress_safe_partial_usingDict() : Behaves the same as LZ4_decompress_safe_partial() with the added ability to specify a memory segment for past data. Performance tip : Decompression speed can be substantially increased when dst == dictStart + dictSize.

! LZ4_decompress_safe_usingDict() : Works the same as a combination of LZ4_setStreamDecode() followed by LZ4_decompress_safe_continue() However, it's stateless: it doesn't need any LZ4_streamDecode_t state. Dictionary is presumed stable : it must remain accessible and unmodified during decompression. Performance tip : Decompression speed can be substantially increased when dst == dictStart + dictSize.

! LZ4_loadDict() : Use this function to reference a static dictionary into LZ4_stream_t. The dictionary must remain available during compression. LZ4_loadDict() triggers a reset, so any previous data will be forgotten. The same dictionary will have to be loaded on decompression side for successful decoding. Dictionary are useful for better compression of small data (KB range). While LZ4 itself accepts any input as dictionary, dictionary efficiency is also a topic. When in doubt, employ the Zstandard's Dictionary Builder. Loading a size of 0 is allowed, and is the same as reset. @return : loaded dictionary size, in bytes (note: only the last 64 KB are loaded)

! LZ4_loadDictSlow() : v1.10.0+ Same as LZ4_loadDict(), but uses a bit more cpu to reference the dictionary content more thoroughly. This is expected to slightly improve compression ratio. The extra-cpu cost is likely worth it if the dictionary is re-used across multiple sessions. @return : loaded dictionary size, in bytes (note: only the last 64 KB are loaded)

v1.9.0+

! LZ4_resetStream_fast() : v1.9.0+ Use this to prepare an LZ4_stream_t for a new chain of dependent blocks (e.g., LZ4_compress_fast_continue()).

An LZ4_stream_t must be initialized once before usage. This is automatically done when created by LZ4_createStream(). However, should the LZ4_stream_t be simply declared on stack (for example), it's necessary to initialize it first, using LZ4_initStream().

After init, start any new stream with LZ4_resetStream_fast(). A same LZ4_stream_t can be re-used multiple times consecutively and compress multiple streams, provided that it starts each new stream with LZ4_resetStream_fast().

LZ4_resetStream_fast() is much faster than LZ4_initStream(), but is not compatible with memory regions containing garbage data.

Note: it's only useful to call LZ4_resetStream_fast() in the context of streaming compression. The extState functions perform their own resets. Invoking LZ4_resetStream_fast() before is redundant, and even counterproductive.

! LZ4_saveDict() : If last 64KB data cannot be guaranteed to remain available at its current memory location, save it into a safer place (char* safeBuffer). This is schematically equivalent to a memcpy() followed by LZ4_loadDict(), but is much faster, because LZ4_saveDict() doesn't need to rebuild tables. @return : saved dictionary size in bytes (necessarily <= maxDictSize), or 0 if error.

! LZ4_setStreamDecode() : An LZ4_streamDecode_t context can be allocated once and re-used multiple times. Use this function to start decompression of a new stream of blocks. A dictionary can optionally be set. Use NULL or size 0 for a reset order. Dictionary is presumed stable : it must remain accessible and unmodified during next decompression. @return : 1 if OK, 0 if error

! LZ4_compress_fast_extState() : Same as LZ4_compress_fast(), using an externally allocated memory space for its state. Use LZ4_sizeofState() to know how much memory must be allocated, and allocate it on 8-bytes boundaries (using malloc() typically). Then, provide this buffer as void* state to compression function.

! LZ4_compress_HC_extStateHC() : Same as LZ4_compress_HC(), but using an externally allocated memory segment for state. state size is provided by LZ4_sizeofStateHC(). Memory segment must be aligned on 8-bytes boundaries (which a normal malloc() should do properly).

library version number; useful to check dll version; requires v1.3.0+

library version string; useful to check dll version; requires v1.7.5+