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| <title>1.9.0 Manual</title> |
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| <body> |
| <h1>1.9.0 Manual</h1> |
| <hr> |
| <a name="Contents"></a><h2>Contents</h2> |
| <ol> |
| <li><a href="#Chapter1">Introduction</a></li> |
| <li><a href="#Chapter2">Version</a></li> |
| <li><a href="#Chapter3">Tuning parameter</a></li> |
| <li><a href="#Chapter4">Simple Functions</a></li> |
| <li><a href="#Chapter5">Advanced Functions</a></li> |
| <li><a href="#Chapter6">Streaming Compression Functions</a></li> |
| <li><a href="#Chapter7">Streaming Decompression Functions</a></li> |
| <li><a href="#Chapter8">Experimental section</a></li> |
| <li><a href="#Chapter9">PRIVATE DEFINITIONS</a></li> |
| <li><a href="#Chapter10">Obsolete Functions</a></li> |
| </ol> |
| <hr> |
| <a name="Chapter1"></a><h2>Introduction</h2><pre> |
| LZ4 is lossless compression algorithm, providing compression speed at 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. |
| 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 provides block compression functions. It gives full buffer control to user. |
| Decompressing an lz4-compressed block also requires metadata (such as compressed size). |
| Each application is free to encode such metadata in whichever way it wants. |
| |
| An additional format, called LZ4 frame specification (doc/lz4_Frame_format.md), |
| take care of encoding standard metadata alongside LZ4-compressed blocks. |
| Frame format is required for interoperability. |
| It is delivered through a companion API, declared in lz4frame.h. |
| <BR></pre> |
| |
| <a name="Chapter2"></a><h2>Version</h2><pre></pre> |
| |
| <pre><b>int LZ4_versionNumber (void); </b>/**< library version number; useful to check dll version */<b> |
| </b></pre><BR> |
| <pre><b>const char* LZ4_versionString (void); </b>/**< library version string; useful to check dll version */<b> |
| </b></pre><BR> |
| <a name="Chapter3"></a><h2>Tuning parameter</h2><pre></pre> |
| |
| <pre><b>#ifndef LZ4_MEMORY_USAGE |
| # define LZ4_MEMORY_USAGE 14 |
| #endif |
| </b><p> Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.) |
| Increasing memory usage improves compression ratio. |
| Reduced memory usage may improve speed, thanks to better cache locality. |
| Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache |
| |
| </p></pre><BR> |
| |
| <a name="Chapter4"></a><h2>Simple Functions</h2><pre></pre> |
| |
| <pre><b>int LZ4_compress_default(const char* src, char* dst, int srcSize, int dstCapacity); |
| </b><p> 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). |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_decompress_safe (const char* src, char* dst, int compressedSize, int dstCapacity); |
| </b><p> compressedSize : is the exact complete size of the compressed block. |
| dstCapacity : is the size of destination buffer, which must be already allocated. |
| @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 : This function is protected against malicious data packets (never writes outside 'dst' buffer, nor read outside 'source' buffer). |
| </p></pre><BR> |
| |
| <a name="Chapter5"></a><h2>Advanced Functions</h2><pre></pre> |
| |
| <pre><b>int LZ4_compressBound(int inputSize); |
| </b><p> 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) |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_compress_fast (const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); |
| </b><p> 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 ACCELERATION_DEFAULT (currently == 1, see lz4.c). |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_sizeofState(void); |
| int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); |
| </b><p> 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. |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_compress_destSize (const char* src, char* dst, int* srcSizePtr, int targetDstSize); |
| </b><p> 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. |
| @return : Nb bytes written into 'dst' (necessarily <= targetDestSize) |
| or 0 if compression fails. |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity); |
| </b><p> 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, |
| which can boost performance when only the beginning of a block is required. |
| |
| @return : the number of bytes decoded in `dst` (necessarily <= dstCapacity) |
| If source stream is detected malformed, function returns a negative result. |
| |
| Note : @return can be < targetOutputSize, if compressed block contains less data. |
| |
| Note 2 : this function features 2 parameters, targetOutputSize and dstCapacity, |
| and expects targetOutputSize <= dstCapacity. |
| It effectively stops decoding on reaching targetOutputSize, |
| so dstCapacity is kind of redundant. |
| This is because in a previous version of this function, |
| decoding operation would not "break" a sequence in the middle. |
| As a consequence, there was no guarantee that decoding would stop 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. |
| This is no longer necessary. |
| The function nonetheless keeps its signature, in an effort to not break API. |
| |
| </p></pre><BR> |
| |
| <a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre> |
| |
| <pre><b>void LZ4_resetStream_fast (LZ4_stream_t* streamPtr); |
| </b><p> 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. |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize); |
| </b><p> Use this function to load a static dictionary into LZ4_stream_t. |
| Any previous data will be forgotten, only 'dictionary' will remain in memory. |
| Loading a size of 0 is allowed, and is the same as reset. |
| @return : dictionary size, in bytes (necessarily <= 64 KB) |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); |
| </b><p> 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. |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int maxDictSize); |
| </b><p> 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. |
| |
| </p></pre><BR> |
| |
| <a name="Chapter7"></a><h2>Streaming Decompression Functions</h2><pre> Bufferless synchronous API |
| <BR></pre> |
| |
| <pre><b>LZ4_streamDecode_t* LZ4_createStreamDecode(void); |
| int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream); |
| </b><p> creation / destruction of streaming decompression tracking context. |
| A tracking context can be re-used multiple times. |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize); |
| </b><p> 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 |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_decoderRingBufferSize(int maxBlockSize); |
| #define LZ4_DECODER_RING_BUFFER_SIZE(maxBlockSize) (65536 + 14 + (maxBlockSize)) </b>/* for static allocation; maxBlockSize presumed valid */<b> |
| </b><p> 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). |
| |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int srcSize, int dstCapacity); |
| </b><p> 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. |
| </p></pre><BR> |
| |
| <pre><b>int LZ4_decompress_safe_usingDict (const char* src, char* dst, int srcSize, int dstCapcity, const char* dictStart, int dictSize); |
| </b><p> 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. |
| |
| </p></pre><BR> |
| |
| <a name="Chapter8"></a><h2>Experimental section</h2><pre> |
| Symbols declared in this section must be considered unstable. Their |
| signatures or semantics may change, or they may be removed altogether in the |
| future. They are therefore only safe to depend on when the caller is |
| statically linked against the library. |
| |
| To protect against unsafe usage, not only are the declarations guarded, |
| the definitions are hidden by default |
| when building LZ4 as a shared/dynamic library. |
| |
| In order to access these declarations, |
| define LZ4_STATIC_LINKING_ONLY in your application |
| before including LZ4's headers. |
| |
| In order to make their implementations accessible dynamically, you must |
| define LZ4_PUBLISH_STATIC_FUNCTIONS when building the LZ4 library. |
| <BR></pre> |
| |
| <pre><b>LZ4LIB_STATIC_API int LZ4_compress_fast_extState_fastReset (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); |
| </b><p> A variant of LZ4_compress_fast_extState(). |
| |
| Using this variant avoids an expensive initialization step. |
| It is only safe to call if the state buffer is known to be correctly initialized already |
| (see above comment on LZ4_resetStream_fast() for a definition of "correctly initialized"). |
| From a high level, the difference is that |
| this function initializes the provided state with a call to something like LZ4_resetStream_fast() |
| while LZ4_compress_fast_extState() starts with a call to LZ4_resetStream(). |
| |
| </p></pre><BR> |
| |
| <pre><b>LZ4LIB_STATIC_API void LZ4_attach_dictionary(LZ4_stream_t* workingStream, const LZ4_stream_t* dictionaryStream); |
| </b><p> This is an experimental API that allows |
| efficient 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_stream_t into a |
| working LZ4_stream_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_loadDict() 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. The dictionary |
| stream (and source buffer) must remain in-place / accessible / unchanged |
| through the completion of the first compression call on the stream. |
| |
| </p></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 code to API and/or ABI break in future versions of the library. |
| <BR></pre> |
| |
| <pre><b>typedef struct { |
| const uint8_t* externalDict; |
| size_t extDictSize; |
| const uint8_t* prefixEnd; |
| size_t prefixSize; |
| } LZ4_streamDecode_t_internal; |
| </b></pre><BR> |
| <pre><b>typedef struct { |
| const unsigned char* externalDict; |
| const unsigned char* prefixEnd; |
| size_t extDictSize; |
| size_t prefixSize; |
| } LZ4_streamDecode_t_internal; |
| </b></pre><BR> |
| <pre><b>#define LZ4_STREAMSIZE_U64 ((1 << (LZ4_MEMORY_USAGE-3)) + 4 + ((sizeof(void*)==16) ? 4 : 0) </b>/*AS-400*/ )<b> |
| #define LZ4_STREAMSIZE (LZ4_STREAMSIZE_U64 * sizeof(unsigned long long)) |
| union LZ4_stream_u { |
| unsigned long long table[LZ4_STREAMSIZE_U64]; |
| LZ4_stream_t_internal internal_donotuse; |
| } ; </b>/* previously typedef'd to LZ4_stream_t */<b> |
| </b><p> information structure to track an LZ4 stream. |
| 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 a future version. |
| |
| </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. |
| |
| </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 |
| # define LZ4_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__) |
| # if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b> |
| # define LZ4_DEPRECATED(message) [[deprecated(message)]] |
| # elif (LZ4_GCC_VERSION >= 405) || defined(__clang__) |
| # define LZ4_DEPRECATED(message) __attribute__((deprecated(message))) |
| # elif (LZ4_GCC_VERSION >= 301) |
| # define LZ4_DEPRECATED(message) __attribute__((deprecated)) |
| # elif defined(_MSC_VER) |
| # define LZ4_DEPRECATED(message) __declspec(deprecated(message)) |
| # else |
| # pragma message("WARNING: You need to implement LZ4_DEPRECATED for this compiler") |
| # define LZ4_DEPRECATED(message) |
| # 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("This function is deprecated and unsafe. Consider using LZ4_decompress_safe() instead") LZ4LIB_API |
| 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") LZ4LIB_API |
| 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") LZ4LIB_API |
| int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize); |
| </b><p> These functions used to be a bit faster than LZ4_decompress_safe(), |
| but situation has changed in recent versions. |
| Now, `LZ4_decompress_safe()` is as fast and sometimes even faster than `LZ4_decompress_fast()`. |
| Moreover, LZ4_decompress_safe() is protected vs malformed input, while `LZ4_decompress_fast()` is not, making it a security liability. |
| As a consequence, LZ4_decompress_fast() is strongly discouraged, and deprecated. |
| |
| Last LZ4_decompress_fast() specificity is that it can decompress a block without knowing its compressed size. |
| Note that even that functionality could be achieved in a more secure manner if need be, |
| though it would require new prototypes, and adaptation of the implementation to this new use case. |
| |
| 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, and overflow input buffer. |
| Also, since match offsets are not validated, match reads from 'src' may underflow. |
| These issues never happen if input 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> |
| |
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