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diff --git a/doc/lz4_manual.html b/doc/lz4_manual.html new file mode 100644 index 0000000..838dbf4 --- /dev/null +++ b/doc/lz4_manual.html @@ -0,0 +1,240 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>lz4 1.7.2 Manual</title> +</head> +<body> +<h1>lz4 1.7.2 Manual</h1> +<hr> +<a name="Contents"></a><h2>Contents</h2> +<ol> +<li><a href="#Chapter1">Introduction</a></li> +<li><a href="#Chapter2">Tuning parameter</a></li> +<li><a href="#Chapter3">Simple Functions</a></li> +<li><a href="#Chapter4">Advanced Functions</a></li> +<li><a href="#Chapter5">Streaming Compression Functions</a></li> +<li><a href="#Chapter6">Streaming Decompression Functions</a></li> +</ol> +<hr> +<a name="Chapter1"></a><h2>Introduction</h2><pre> + LZ4 is lossless compression algorithm, providing compression speed at 400 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. + Block compression functions are not-enough to send information, + since it's still necessary to provide metadata (such as compressed size), + and each application can do it in whichever way it wants. + For interoperability, there is LZ4 frame specification (doc/lz4_Frame_format.md). + A library is provided to take care of it, see lz4frame.h. +<BR></pre> + +<h3>Version</h3><pre><b>int LZ4_versionNumber (void); +const char* LZ4_versionString (void); +</b></pre><BR> +<a name="Chapter2"></a><h2>Tuning parameter</h2><pre></pre> + +<pre><b>#define LZ4_MEMORY_USAGE 14 +</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 can improve speed, due to cache effect + Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache + +</p></pre><BR> + +<a name="Chapter3"></a><h2>Simple Functions</h2><pre></pre> + +<pre><b>int LZ4_compress_default(const char* source, char* dest, int sourceSize, int maxDestSize); +</b><p> Compresses 'sourceSize' bytes from buffer 'source' + into already allocated 'dest' buffer of size 'maxDestSize'. + Compression is guaranteed to succeed if 'maxDestSize' >= LZ4_compressBound(sourceSize). + It also runs faster, so it's a recommended setting. + If the function cannot compress 'source' into a more limited 'dest' budget, + compression stops *immediately*, and the function result is zero. + As a consequence, 'dest' content is not valid. + This function never writes outside 'dest' buffer, nor read outside 'source' buffer. + sourceSize : Max supported value is LZ4_MAX_INPUT_VALUE + maxDestSize : full or partial size of buffer 'dest' (which must be already allocated) + return : the number of bytes written into buffer 'dest' (necessarily <= maxOutputSize) + or 0 if compression fails +</p></pre><BR> + +<pre><b>int LZ4_decompress_safe (const char* source, char* dest, int compressedSize, int maxDecompressedSize); +</b><p> compressedSize : is the precise full size of the compressed block. + maxDecompressedSize : is the size of destination buffer, which must be already allocated. + return : the number of bytes decompressed into destination buffer (necessarily <= maxDecompressedSize) + If destination buffer is not large enough, decoding will stop and output an error code (<0). + If the source stream is detected malformed, the function will stop decoding and return a negative result. + This function is protected against buffer overflow exploits, including malicious data packets. + It never writes outside output buffer, nor reads outside input buffer. +</p></pre><BR> + +<a name="Chapter4"></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() compress faster when dest buffer size 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 too large ( > LZ4_MAX_INPUT_SIZE) +</p></pre><BR> + +<pre><b>int LZ4_compress_fast (const char* source, char* dest, int sourceSize, int maxDestSize, int acceleration); +</b><p> Same as LZ4_compress_default(), but allows to select an "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 (see lz4.c), which is 1. +</p></pre><BR> + +<pre><b>int LZ4_sizeofState(void); +int LZ4_compress_fast_extState (void* state, const char* source, char* dest, int inputSize, int maxDestSize, int acceleration); +</b><p> Same compression function, just using an externally allocated memory space to store compression state. + Use LZ4_sizeofState() to know how much memory must be allocated, + and allocate it on 8-bytes boundaries (using malloc() typically). + Then, provide it as 'void* state' to compression function. +</p></pre><BR> + +<pre><b>int LZ4_compress_destSize (const char* source, char* dest, int* sourceSizePtr, int targetDestSize); +</b><p> Reverse the logic, by compressing as much data as possible from 'source' buffer + into already allocated buffer 'dest' of size 'targetDestSize'. + This function either compresses the entire 'source' content into 'dest' if it's large enough, + or fill 'dest' buffer completely with as much data as possible from 'source'. + *sourceSizePtr : will be modified to indicate how many bytes where read from 'source' to fill 'dest'. + New value is necessarily <= old value. + return : Nb bytes written into 'dest' (necessarily <= targetDestSize) + or 0 if compression fails +</p></pre><BR> + +<pre><b>int LZ4_decompress_fast (const char* source, char* dest, int originalSize); +</b><p> originalSize : is the original and therefore uncompressed size + return : the number of bytes read from the source buffer (in other words, the compressed size) + If the source stream is detected malformed, the function will stop decoding and return a negative result. + Destination buffer must be already allocated. Its size must be a minimum of 'originalSize' bytes. + note : This function fully respect memory boundaries for properly formed compressed data. + It is a bit faster than LZ4_decompress_safe(). + However, it does not provide any protection against intentionally modified data stream (malicious input). + Use this function in trusted environment only (data to decode comes from a trusted source). +</p></pre><BR> + +<pre><b>int LZ4_decompress_safe_partial (const char* source, char* dest, int compressedSize, int targetOutputSize, int maxDecompressedSize); +</b><p> This function decompress a compressed block of size 'compressedSize' at position 'source' + into destination buffer 'dest' of size 'maxDecompressedSize'. + The function tries to stop decompressing operation as soon as 'targetOutputSize' has been reached, + reducing decompression time. + return : the number of bytes decoded in the destination buffer (necessarily <= maxDecompressedSize) + Note : this number can be < 'targetOutputSize' should the compressed block to decode be smaller. + Always control how many bytes were decoded. + If the source stream is detected malformed, the function will stop decoding and return a negative result. + This function never writes outside of output buffer, and never reads outside of input buffer. It is therefore protected against malicious data packets +</p></pre><BR> + +<a name="Chapter5"></a><h2>Streaming Compression Functions</h2><pre></pre> + +<pre><b>typedef struct { long long table[LZ4_STREAMSIZE_U64]; } LZ4_stream_t; +</b><p> information structure to track an LZ4 stream. + important : init this structure content before first use ! + note : only allocated directly the structure if you are statically linking LZ4 + If you are using liblz4 as a DLL, please use below construction methods instead. + +</p></pre><BR> + +<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr); +</b><p> Use this function to init an allocated `LZ4_stream_t` structure + +</p></pre><BR> + +<pre><b>LZ4_stream_t* LZ4_createStream(void); +int LZ4_freeStream (LZ4_stream_t* streamPtr); +</b><p> LZ4_createStream() will allocate and initialize an `LZ4_stream_t` structure. + LZ4_freeStream() releases its memory. + In the context of a DLL (liblz4), please use these methods rather than the static struct. + They are more future proof, in case of a change of `LZ4_stream_t` size. + +</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. + Any previous data will be forgotten, only 'dictionary' will remain in memory. + Loading a size of 0 is allowed. + 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 maxDstSize, int acceleration); +</b><p> Compress buffer content 'src', using data from previously compressed blocks as dictionary to improve compression ratio. + Important : Previous data blocks are assumed to still be present and unmodified ! + 'dst' buffer must be already allocated. + If maxDstSize >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster. + If not, and if compressed data cannot fit into 'dst' buffer size, compression stops, and function returns a zero. + +</p></pre><BR> + +<pre><b>int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int dictSize); +</b><p> 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. + +</p></pre><BR> + +<a name="Chapter6"></a><h2>Streaming Decompression Functions</h2><pre></pre> + +<pre><b>typedef struct { unsigned long long table[LZ4_STREAMDECODESIZE_U64]; } LZ4_streamDecode_t; +</b></pre><BR> +<pre><b>LZ4_streamDecode_t* LZ4_createStreamDecode(void); +int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream); +</b><p> information structure to track an LZ4 stream. + init this structure content using LZ4_setStreamDecode or memset() before first use ! + + In the context of a DLL (liblz4) please prefer usage of construction methods below. + They are more future proof, in case of a change of LZ4_streamDecode_t size in the future. + LZ4_createStreamDecode will allocate and initialize an LZ4_streamDecode_t structure + LZ4_freeStreamDecode releases its memory. + +</p></pre><BR> + +<pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize); +</b><p> Use this function to instruct where to find the dictionary. + Setting a size of 0 is allowed (same effect as reset). + @return : 1 if OK, 0 if error + +</p></pre><BR> + +<pre><b>int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* source, char* dest, int compressedSize, int maxDecompressedSize); +int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* source, char* dest, int originalSize); +</b><p> These decoding functions allow decompression of multiple blocks in "streaming" mode. + Previously decoded blocks *must* remain available at the memory position where they were decoded (up to 64 KB) + In the case of a ring buffers, decoding buffer must be either : + - Exactly same size as encoding buffer, with same update rule (block boundaries at same positions) + In which case, the decoding & encoding ring buffer can have any size, including very small ones ( < 64 KB). + - Larger than encoding buffer, by a minimum of maxBlockSize more bytes. + maxBlockSize is implementation dependent. It's the maximum size you intend to compress into a single block. + 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). + - _At least_ 64 KB + 8 bytes + maxBlockSize. + In which case, encoding and decoding buffers do not need to be synchronized, + and encoding ring buffer can have any size, including larger than decoding buffer. + Whenever these conditions are not possible, save the last 64KB of decoded data into a safe buffer, + and indicate where it is saved using LZ4_setStreamDecode() +</p></pre><BR> + +<pre><b>int LZ4_decompress_safe_usingDict (const char* source, char* dest, int compressedSize, int maxDecompressedSize, const char* dictStart, int dictSize); +int LZ4_decompress_fast_usingDict (const char* source, char* dest, int originalSize, const char* dictStart, int dictSize); +</b><p>Advanced decoding functions : + These decoding functions work the same as + a combination of LZ4_setStreamDecode() followed by LZ4_decompress_x_continue() + They are stand-alone. They don't need nor update an LZ4_streamDecode_t structure. +</p></pre><BR> + +</html> +</body> |