From 93e2477ca4271a9c97e99863ad7f062cdeb92e0a Mon Sep 17 00:00:00 2001 From: Przemyslaw Skibinski Date: Thu, 10 Nov 2016 17:22:26 +0100 Subject: added lz4_manual.html --- doc/lz4_manual.html | 240 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 240 insertions(+) create mode 100644 doc/lz4_manual.html 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 @@ + + + +lz4 1.7.2 Manual + + +

lz4 1.7.2 Manual

Introduction
Tuning parameter
Simple Functions
Advanced Functions
Streaming Compression Functions
Streaming Decompression Functions

Introduction

+  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.
+

+ +

Version

int LZ4_versionNumber (void);
+const char* LZ4_versionString (void);
+

Tuning parameter

+ +

#define LZ4_MEMORY_USAGE 14
+ 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
+ 
+

+ +

Simple Functions

+ +

int LZ4_compress_default(const char* source, char* dest, int sourceSize, int maxDestSize);
+    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 
+

+ +

int LZ4_decompress_safe (const char* source, char* dest, int compressedSize, int maxDecompressedSize);
+    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.
+

+ +

Advanced Functions

+ +

int LZ4_compressBound(int inputSize);
+    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)
+

+ +

int LZ4_compress_fast (const char* source, char* dest, int sourceSize, int maxDestSize, int acceleration);
+    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.
+

+ +

int LZ4_sizeofState(void);
+int LZ4_compress_fast_extState (void* state, const char* source, char* dest, int inputSize, int maxDestSize, int acceleration);
+    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.
+

+ +

int LZ4_compress_destSize (const char* source, char* dest, int* sourceSizePtr, int targetDestSize);
+    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
+

+ +

int LZ4_decompress_fast (const char* source, char* dest, int originalSize);
+    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).
+

+ +

int LZ4_decompress_safe_partial (const char* source, char* dest, int compressedSize, int targetOutputSize, int maxDecompressedSize);
+    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
+

+ +

Streaming Compression Functions

+ +

typedef struct { long long table[LZ4_STREAMSIZE_U64]; } LZ4_stream_t;
+ 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.
+ 
+

+ +

void LZ4_resetStream (LZ4_stream_t* streamPtr);
+  Use this function to init an allocated `LZ4_stream_t` structure
+ 
+

+ +

LZ4_stream_t* LZ4_createStream(void);
+int           LZ4_freeStream (LZ4_stream_t* streamPtr);
+  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.
+ 
+

+ +

int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize);
+  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)
+ 
+

+ +

int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int maxDstSize, int acceleration);
+  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.
+ 
+

+ +

int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int dictSize);
+  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.
+ 
+

+ +

Streaming Decompression Functions

+ +

typedef struct { unsigned long long table[LZ4_STREAMDECODESIZE_U64]; } LZ4_streamDecode_t;
+

LZ4_streamDecode_t* LZ4_createStreamDecode(void); +int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream); +

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. + +

+ +

int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize);
+  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
+ 
+

+ +

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);
+    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()
+

+ +

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);
+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.
+

+ + + -- cgit v0.12