diff options
Diffstat (limited to 'lib/lz4.h')
| -rw-r--r-- | lib/lz4.h | 83 |
1 files changed, 78 insertions, 5 deletions
@@ -65,9 +65,9 @@ extern "C" { Blocks are different from Frames (doc/lz4_Frame_format.md). Frames bundle both blocks and metadata in a specified manner. - This are required for compressed data to be self-contained and portable. + 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. - Note that the `lz4` CLI can only manage frames. + The `lz4` CLI can only manage frames. */ /*^*************************************************************** @@ -388,6 +388,8 @@ LZ4LIB_API int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecod */ LZ4LIB_API int LZ4_decompress_safe_usingDict (const char* src, char* dst, int srcSize, int dstCapcity, const char* dictStart, int dictSize); +#endif /* LZ4_H_2983827168210 */ + /*^************************************* * !!!!!! STATIC LINKING ONLY !!!!!! @@ -413,14 +415,17 @@ LZ4LIB_API int LZ4_decompress_safe_usingDict (const char* src, char* dst, int sr * define LZ4_PUBLISH_STATIC_FUNCTIONS when building the LZ4 library. ******************************************************************************/ +#ifdef LZ4_STATIC_LINKING_ONLY + +#ifndef LZ4_STATIC_3504398509 +#define LZ4_STATIC_3504398509 + #ifdef LZ4_PUBLISH_STATIC_FUNCTIONS #define LZ4LIB_STATIC_API LZ4LIB_API #else #define LZ4LIB_STATIC_API #endif -#ifdef LZ4_STATIC_LINKING_ONLY - /*! LZ4_compress_fast_extState_fastReset() : * A variant of LZ4_compress_fast_extState(). @@ -462,8 +467,75 @@ LZ4LIB_STATIC_API int LZ4_compress_fast_extState_fastReset (void* state, const c */ LZ4LIB_STATIC_API void LZ4_attach_dictionary(LZ4_stream_t* workingStream, const LZ4_stream_t* dictionaryStream); + +/*! In-place compression and decompression + * + * It's possible to have input and output sharing the same buffer, + * for highly contrained memory environments. + * In both cases, it requires input to lay at the end of the buffer, + * and decompression to start at beginning of the buffer. + * Buffer size must feature some margin, hence be larger than final size. + * + * |<------------------------buffer--------------------------------->| + * |<-----------compressed data--------->| + * |<-----------decompressed size------------------>| + * |<----margin---->| + * + * This technique is more useful for decompression, + * since decompressed size is typically larger, + * and margin is short. + * + * In-place decompression will work inside any buffer + * which size is >= LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize). + * This presumes that decompressedSize > compressedSize. + * Otherwise, it means compression actually expanded data, + * and it would be more efficient to store such data with a flag indicating it's not compressed. + * This can happen when data is not compressible (already compressed, or encrypted). + * + * For in-place compression, margin is larger, as it must be able to cope with both + * history preservation, requiring input data to remain unmodified up to LZ4_DISTANCE_MAX, + * and data expansion, which can happen when input is not compressible. + * As a consequence, buffer size requirements are much higher, + * and memory savings offered by in-place compression are more limited. + * + * There are ways to limit this cost for compression : + * - Reduce history size, by modifying LZ4_DISTANCE_MAX. + * Note that it is a compile-time constant, so all compressions will apply this limit. + * Lower values will reduce compression ratio, except when input_size < LZ4_DISTANCE_MAX, + * so it's a reasonable trick when inputs are known to be small. + * - Require the compressor to deliver a "maximum compressed size". + * This is the `dstCapacity` parameter in `LZ4_compress*()`. + * When this size is < LZ4_COMPRESSBOUND(inputSize), then compression can fail, + * in which case, the return code will be 0 (zero). + * The caller must be ready for these cases to happen, + * and typically design a backup scheme to send data uncompressed. + * The combination of both techniques can significantly reduce + * the amount of margin required for in-place compression. + * + * In-place compression can work in any buffer + * which size is >= (maxCompressedSize) + * with maxCompressedSize == LZ4_COMPRESSBOUND(srcSize) for guaranteed compression success. + * LZ4_COMPRESS_INPLACE_BUFFER_SIZE() depends on both maxCompressedSize and LZ4_DISTANCE_MAX, + * so it's possible to reduce memory requirements by playing with them. + */ + +#define LZ4_DECOMPRESS_INPLACE_MARGIN(compressedSize) (((compressedSize) >> 8) + 32) +#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ((decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) /**< note: presumes that compressedSize < decompressedSize. note2: margin is overestimated a bit, since it could use compressedSize instead */ + +#ifndef LZ4_DISTANCE_MAX /* history window size; can be user-defined at compile time */ +# define LZ4_DISTANCE_MAX 65535 /* set to maximum value by default */ #endif +#define LZ4_COMPRESS_INPLACE_MARGIN (LZ4_DISTANCE_MAX + 32) /* LZ4_DISTANCE_MAX can be safely replaced by srcSize when it's smaller */ +#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ((maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) /**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */ + +#endif /* LZ4_STATIC_3504398509 */ +#endif /* LZ4_STATIC_LINKING_ONLY */ + + + +#ifndef LZ4_H_98237428734687 +#define LZ4_H_98237428734687 /*-************************************************************ * PRIVATE DEFINITIONS @@ -567,6 +639,7 @@ union LZ4_streamDecode_u { } ; /* previously typedef'd to LZ4_streamDecode_t */ + /*-************************************ * Obsolete Functions **************************************/ @@ -674,7 +747,7 @@ LZ4LIB_API int LZ4_decompress_fast_usingDict (const char* src, char* dst, int or LZ4LIB_API void LZ4_resetStream (LZ4_stream_t* streamPtr); -#endif /* LZ4_H_2983827168210 */ +#endif /* LZ4_H_98237428734687 */ #if defined (__cplusplus) |