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UDocumentation UE5.7 10.02.2026 (Source)
API documentation for Unreal Engine 5.7
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UDocumentation UE5.7 10.02.2026 (Source)
API documentation for Unreal Engine 5.7
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#include "HAL/PlatformMemory.h"Go to the source code of this file.
Classes | |
| struct | LZ4_stream_t_internal |
| union | LZ4_stream_u |
| struct | LZ4_streamDecode_t_internal |
| union | LZ4_streamDecode_u |
| #define LZ4_COMPRESSBOUND | ( | isize | ) | ((unsigned)(isize) > (unsigned)LZ4_MAX_INPUT_SIZE ? 0 : (isize) + ((isize)/255) + 16) |
| #define LZ4_DECODER_RING_BUFFER_SIZE | ( | maxBlockSize | ) | (65536 + 14 + (maxBlockSize)) /* for static allocation; maxBlockSize presumed valid */ |
| #define LZ4_FREESTANDING 0 |
LZ4_FREESTANDING : When this macro is set to 1, it enables "freestanding mode" that is suitable for typical freestanding environment which doesn't support standard C library.
| #define LZ4_H_2983827168210 |
| #define LZ4_H_98237428734687 |
| #define LZ4_HASH_SIZE_U32 (1 << LZ4_HASHLOG) /* required as macro for static allocation */ |
| #define LZ4_HASHLOG (LZ4_MEMORY_USAGE-2) |
| #define LZ4_HASHTABLESIZE (1 << LZ4_MEMORY_USAGE) |
| #define LZ4_LIB_VERSION LZ4_VERSION_MAJOR.LZ4_VERSION_MINOR.LZ4_VERSION_RELEASE |
| #define LZ4_MAX_INPUT_SIZE 0x7E000000 /* 2 113 929 216 bytes */ |
| #define LZ4_MEMORY_USAGE LZ4_MEMORY_USAGE_DEFAULT |
LZ4_MEMORY_USAGE : Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; ) Increasing memory usage improves compression ratio, at the cost of speed. Reduced memory usage may improve speed at the cost of ratio, thanks to better cache locality. Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache
| #define LZ4_MEMORY_USAGE_DEFAULT 14 |
| #define LZ4_MEMORY_USAGE_MAX 20 |
| #define LZ4_MEMORY_USAGE_MIN 10 |
| #define LZ4_QUOTE | ( | str | ) | #str |
| #define LZ4_STREAM_MINSIZE ((1UL << LZ4_MEMORY_USAGE) + 32) /* static size, for inter-version compatibility */ |
| #define LZ4_STREAMDECODE_MINSIZE 32 |
| #define LZ4_VERSION_MINOR 9 /* for new (non-breaking) interface capabilities */ |
| #define LZ4_VERSION_NUMBER (LZ4_VERSION_MAJOR *100*100 + LZ4_VERSION_MINOR *100 + LZ4_VERSION_RELEASE) |
| #define LZ4_VERSION_RELEASE 4 /* for tweaks, bug-fixes, or development */ |
| #define LZ4_VERSION_STRING LZ4_EXPAND_AND_QUOTE(LZ4_LIB_VERSION) /* requires v1.7.3+ */ |
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:
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.
LZ4_stream_t : Never ever use below internal definitions directly ! These definitions are not API/ABI safe, and may change in future versions. If you need static allocation, declare or allocate an LZ4_stream_t object.
| LZ4LIB_API int LZ4_compress_default | ( | const char * | src, |
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity | ||
| ) |
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)
| LZ4LIB_API int LZ4_compress_destSize | ( | const char * | src, |
| char * | dst, | ||
| int * | srcSizePtr, | ||
| int | targetDstSize | ||
| ) |
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.
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 | ( | const char * | src, |
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity, | ||
| int | acceleration | ||
| ) |
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).
| LZ4LIB_API int LZ4_compress_fast_continue | ( | LZ4_stream_t * | streamPtr, |
| const char * | src, | ||
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity, | ||
| int | acceleration | ||
| ) |
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.
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_compress_fast_extState | ( | void * | state, |
| const char * | src, | ||
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity, | ||
| int | acceleration | ||
| ) |
| LZ4LIB_API int LZ4_compressBound | ( | int | inputSize | ) |
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)
| LZ4LIB_API LZ4_stream_t * LZ4_createStream | ( | void | ) |
Note about RC_INVOKED
| LZ4LIB_API LZ4_streamDecode_t * LZ4_createStreamDecode | ( | void | ) |
LZ4_createStreamDecode() and LZ4_freeStreamDecode() : creation / destruction of streaming decompression tracking context. A tracking context can be re-used multiple times.
| LZ4LIB_API int LZ4_decoderRingBufferSize | ( | int | maxBlockSize | ) |
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.
LZ4_decoderRingBufferSize() : when setting a ring buffer for streaming decompression (optional scenario), provides the minimum size of this ring buffer to be compatible with any source respecting maxBlockSize condition. Note : in a ring buffer scenario, blocks are presumed decompressed next to each other. When not enough space remains for next block (remainingSize < maxBlockSize), decoding resumes from beginning of ring buffer.
| LZ4LIB_API int LZ4_decompress_safe | ( | const char * | src, |
| char * | dst, | ||
| int | compressedSize, | ||
| int | dstCapacity | ||
| ) |
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.
| LZ4LIB_API int LZ4_decompress_safe_continue | ( | LZ4_streamDecode_t * | LZ4_streamDecode, |
| const char * | src, | ||
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity | ||
| ) |
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 :
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 | ( | const char * | src, |
| char * | dst, | ||
| int | srcSize, | ||
| int | targetOutputSize, | ||
| int | dstCapacity | ||
| ) |
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.
dst (necessarily <= targetOutputSize) If source stream is detected malformed, function returns a negative result.Note 1 :
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.
| LZ4LIB_API int LZ4_decompress_safe_partial_usingDict | ( | const char * | src, |
| char * | dst, | ||
| int | compressedSize, | ||
| int | targetOutputSize, | ||
| int | maxOutputSize, | ||
| const char * | dictStart, | ||
| int | dictSize | ||
| ) |
| LZ4LIB_API int LZ4_decompress_safe_usingDict | ( | const char * | src, |
| char * | dst, | ||
| int | srcSize, | ||
| int | dstCapacity, | ||
| const char * | dictStart, | ||
| int | dictSize | ||
| ) |
LZ4_decompress_*_usingDict() : These decoding functions work the same as a combination of LZ4_setStreamDecode() followed by LZ4_decompress_*_continue() They are stand-alone, and don't need an LZ4_streamDecode_t structure. Dictionary is presumed stable : it must remain accessible and unmodified during decompression. Performance tip : Decompression speed can be substantially increased when dst == dictStart + dictSize.
| LZ4LIB_API int LZ4_freeStream | ( | LZ4_stream_t * | streamPtr | ) |
| LZ4LIB_API int LZ4_freeStreamDecode | ( | LZ4_streamDecode_t * | LZ4_stream | ) |
| LZ4LIB_API LZ4_stream_t * LZ4_initStream | ( | void * | buffer, |
| size_t | size | ||
| ) |
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
Note : initialization fails if size and alignment conditions are not respected. In which case, the function will
| LZ4LIB_API int LZ4_loadDict | ( | LZ4_stream_t * | streamPtr, |
| const char * | dictionary, | ||
| int | 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 accept any input as dictionary, results are generally better when using Zstandard's Dictionary Builder. Loading a size of 0 is allowed, and is the same as reset.
| LZ4LIB_API void LZ4_resetStream | ( | LZ4_stream_t * | streamPtr | ) |
LZ4_resetStream() : 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.
| LZ4LIB_API void LZ4_resetStream_fast | ( | LZ4_stream_t * | streamPtr | ) |
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.
| LZ4LIB_API int LZ4_saveDict | ( | LZ4_stream_t * | LZ4_dict, |
| char * | safeBuffer, | ||
| int | dictSize | ||
| ) |
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.
LZ4_saveDict() : If previously compressed data block is not guaranteed to remain available at its memory location, save it into a safer place (char* safeBuffer). Note : no need to call LZ4_loadDict() afterwards, dictionary is immediately usable, one can therefore call LZ4_compress_fast_continue() right after.
LZ4_saveDict() : If previously compressed data block is not guaranteed to remain available at its memory location, save it into a safer place (char* safeBuffer). Note : you don't need to call LZ4_loadDict() afterwards, dictionary is immediately usable, you can therefore call LZ4_compress_fast_continue(). Return : saved dictionary size in bytes (necessarily <= dictSize), or 0 if error.
| LZ4LIB_API int LZ4_setStreamDecode | ( | LZ4_streamDecode_t * | LZ4_streamDecode, |
| const char * | dictionary, | ||
| int | dictSize | ||
| ) |
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.
LZ4_setStreamDecode() : Use this function to instruct where to find the dictionary. This function is not necessary if previous data is still available where it was decoded. Loading a size of 0 is allowed (same effect as no dictionary).
| LZ4LIB_API int LZ4_sizeofState | ( | void | ) |
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.
| LZ4LIB_API int LZ4_versionNumber | ( | void | ) |
library version number; useful to check dll version; requires v1.3.0+
| LZ4LIB_API const char * LZ4_versionString | ( | void | ) |
library version string; useful to check dll version; requires v1.7.5+
1.9.8