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Diffstat (limited to 'doc/lz4_manual.html')
| -rw-r--r-- | doc/lz4_manual.html | 65 |
1 files changed, 33 insertions, 32 deletions
diff --git a/doc/lz4_manual.html b/doc/lz4_manual.html index 46e6c3d..ef715f8 100644 --- a/doc/lz4_manual.html +++ b/doc/lz4_manual.html @@ -42,9 +42,9 @@ <a name="Chapter2"></a><h2>Version</h2><pre></pre> -<pre><b>int LZ4_versionNumber (void); </b>/**< library version number; to be used when checking dll version */<b> +<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; to be used when checking dll version */<b> +<pre><b>const char* LZ4_versionString (void); </b>/**< library version string; unseful to check dll version */<b> </b></pre><BR> <a name="Chapter3"></a><h2>Tuning parameter</h2><pre></pre> @@ -53,7 +53,7 @@ #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 can improve speed, due to cache effect + Reduced memory usage may improve speed, thanks to cache effect Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache </p></pre><BR> @@ -65,12 +65,12 @@ 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 limited 'dst' budget, + If the function cannot compress 'src' into a more limited 'dst' budget, compression stops *immediately*, and the function result is zero. - As a consequence, 'dst' content is not valid. - This function never writes outside 'dst' buffer, nor read outside 'source' buffer. - srcSize : supported max value is LZ4_MAX_INPUT_VALUE - dstCapacity : full or partial size of buffer 'dst' (which must be already allocated) + Note : as a consequence, 'dst' content is not valid. + Note 2 : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer). + 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 </p></pre><BR> @@ -81,8 +81,7 @@ 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. - This function is protected against buffer overflow exploits, including malicious data packets. - It never writes outside output buffer, nor reads outside input buffer. + This function is protected against malicious data packets. </p></pre><BR> <a name="Chapter5"></a><h2>Advanced Functions</h2><pre></pre> @@ -91,18 +90,18 @@ </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) + 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 too large ( > LZ4_MAX_INPUT_SIZE) + 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 to select an "acceleration" factor. +</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 (see lz4.c), which is 1. + Values <= 0 will be replaced by ACCELERATION_DEFAULT (currently == 1, see lz4.c). </p></pre><BR> <pre><b>int LZ4_sizeofState(void); @@ -125,26 +124,28 @@ int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int src </p></pre><BR> <pre><b>int LZ4_decompress_fast (const char* src, char* dst, int originalSize); -</b><p> originalSize : is the original 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 >= 'originalSize' bytes. +</b><p>This function is a bit faster than LZ4_decompress_safe(), +but doesn't provide any security guarantee. + originalSize : is the uncompressed size to regenerate + Destination buffer must be already allocated, and its size must be >= 'originalSize' bytes. + return : number of bytes read from source buffer (== compressed size). + If the source stream is detected malformed, the function stops decoding and return a negative result. note : This function respects 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). + However, it does not provide any protection against malicious input. + It also doesn't know 'src' size, and implies it's >= compressed size. + Use this function in trusted environment **only**. </p></pre><BR> <pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity); </b><p> This function decompress a compressed block of size 'srcSize' at position 'src' into destination buffer 'dst' of size 'dstCapacity'. The function will decompress a minimum of 'targetOutputSize' bytes, and stop after that. - However, it's not accurate, and may write more than 'targetOutputSize' (but <= dstCapacity). + However, it's not accurate, and may write more than 'targetOutputSize' (but always <= dstCapacity). @return : the number of bytes decoded in the destination buffer (necessarily <= dstCapacity) - Note : this number can be < 'targetOutputSize' should the compressed block contain less data. - 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. + Note : this number can also be < targetOutputSize, if compressed block contains less data. + Therefore, always control how many bytes were decoded. + If source stream is detected malformed, function returns a negative result. + This function is protected against malicious data packets. </p></pre><BR> <a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre> @@ -175,7 +176,8 @@ int LZ4_freeStream (LZ4_stream_t* streamPtr); 'dst' buffer must be already allocated. If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster. - Important : Up to 64KB of previously compressed data is assumed to remain present and unmodified in memory ! + Important : The previous 64KB of compressed data is assumed to remain preset and unmodified in memory! + If less than 64KB has been compressed all the data must be present. Special 1 : If input buffer is a double-buffer, it can have any size, including < 64 KB. Special 2 : If input buffer is a ring-buffer, it can have any size, including < 64 KB. @@ -215,7 +217,8 @@ int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const ch </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 accept one block at a time. - Previously decoded blocks *must* remain available at the memory position where they were decoded (up to 64 KB). + 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 application sets a ring buffer for decompression, it must respect one of the following conditions : - Exactly same size as encoding buffer, with same update rule (block boundaries at same positions) @@ -311,11 +314,9 @@ union LZ4_streamDecode_u { # define LZ4_DEPRECATED(message) </b>/* disable deprecation warnings */<b> #else # define LZ4_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__) -# if defined(__clang__) </b>/* clang doesn't handle mixed C++11 and CNU attributes */<b> -# define LZ4_DEPRECATED(message) __attribute__((deprecated(message))) -# elif defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b> +# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b> # define LZ4_DEPRECATED(message) [[deprecated(message)]] -# elif (LZ4_GCC_VERSION >= 405) +# 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)) |