📝 Editando: lzma12.h

/** * \file lzma/lzma12.h * \brief LZMA1 and LZMA2 filters */ /* * Author: Lasse Collin * * This file has been put into the public domain. * You can do whatever you want with this file. * * See ../lzma.h for information about liblzma as a whole. */ #ifndef LZMA_H_INTERNAL # error Never include this file directly. Use <lzma.h> instead. #endif /** * \brief LZMA1 Filter ID * * LZMA1 is the very same thing as what was called just LZMA in LZMA Utils, * 7-Zip, and LZMA SDK. It's called LZMA1 here to prevent developers from * accidentally using LZMA when they actually want LZMA2. * * LZMA1 shouldn't be used for new applications unless you _really_ know * what you are doing. LZMA2 is almost always a better choice. */ #define LZMA_FILTER_LZMA1 LZMA_VLI_C(0x4000000000000001) /** * \brief LZMA2 Filter ID * * Usually you want this instead of LZMA1. Compared to LZMA1, LZMA2 adds * support for LZMA_SYNC_FLUSH, uncompressed chunks (smaller expansion * when trying to compress uncompressible data), possibility to change * lc/lp/pb in the middle of encoding, and some other internal improvements. */ #define LZMA_FILTER_LZMA2 LZMA_VLI_C(0x21) /** * \brief Match finders * * Match finder has major effect on both speed and compression ratio. * Usually hash chains are faster than binary trees. * * If you will use LZMA_SYNC_FLUSH often, the hash chains may be a better * choice, because binary trees get much higher compression ratio penalty * with LZMA_SYNC_FLUSH. * * The memory usage formulas are only rough estimates, which are closest to * reality when dict_size is a power of two. The formulas are more complex * in reality, and can also change a little between liblzma versions. Use * lzma_raw_encoder_memusage() to get more accurate estimate of memory usage. */ typedef enum { LZMA_MF_HC3 = 0x03, /**< * \brief Hash Chain with 2- and 3-byte hashing * * Minimum nice_len: 3 * * Memory usage: * - dict_size <= 16 MiB: dict_size * 7.5 * - dict_size > 16 MiB: dict_size * 5.5 + 64 MiB */ LZMA_MF_HC4 = 0x04, /**< * \brief Hash Chain with 2-, 3-, and 4-byte hashing * * Minimum nice_len: 4 * * Memory usage: * - dict_size <= 32 MiB: dict_size * 7.5 * - dict_size > 32 MiB: dict_size * 6.5 */ LZMA_MF_BT2 = 0x12, /**< * \brief Binary Tree with 2-byte hashing * * Minimum nice_len: 2 * * Memory usage: dict_size * 9.5 */ LZMA_MF_BT3 = 0x13, /**< * \brief Binary Tree with 2- and 3-byte hashing * * Minimum nice_len: 3 * * Memory usage: * - dict_size <= 16 MiB: dict_size * 11.5 * - dict_size > 16 MiB: dict_size * 9.5 + 64 MiB */ LZMA_MF_BT4 = 0x14 /**< * \brief Binary Tree with 2-, 3-, and 4-byte hashing * * Minimum nice_len: 4 * * Memory usage: * - dict_size <= 32 MiB: dict_size * 11.5 * - dict_size > 32 MiB: dict_size * 10.5 */ } lzma_match_finder; /** * \brief Test if given match finder is supported * * Return true if the given match finder is supported by this liblzma build. * Otherwise false is returned. It is safe to call this with a value that * isn't listed in lzma_match_finder enumeration; the return value will be * false. * * There is no way to list which match finders are available in this * particular liblzma version and build. It would be useless, because * a new match finder, which the application developer wasn't aware, * could require giving additional options to the encoder that the older * match finders don't need. */ extern LZMA_API(lzma_bool) lzma_mf_is_supported(lzma_match_finder match_finder) lzma_nothrow lzma_attr_const; /** * \brief Compression modes * * This selects the function used to analyze the data produced by the match * finder. */ typedef enum { LZMA_MODE_FAST = 1, /**< * \brief Fast compression * * Fast mode is usually at its best when combined with * a hash chain match finder. */ LZMA_MODE_NORMAL = 2 /**< * \brief Normal compression * * This is usually notably slower than fast mode. Use this * together with binary tree match finders to expose the * full potential of the LZMA1 or LZMA2 encoder. */ } lzma_mode; /** * \brief Test if given compression mode is supported * * Return true if the given compression mode is supported by this liblzma * build. Otherwise false is returned. It is safe to call this with a value * that isn't listed in lzma_mode enumeration; the return value will be false. * * There is no way to list which modes are available in this particular * liblzma version and build. It would be useless, because a new compression * mode, which the application developer wasn't aware, could require giving * additional options to the encoder that the older modes don't need. */ extern LZMA_API(lzma_bool) lzma_mode_is_supported(lzma_mode mode) lzma_nothrow lzma_attr_const; /** * \brief Options specific to the LZMA1 and LZMA2 filters * * Since LZMA1 and LZMA2 share most of the code, it's simplest to share * the options structure too. For encoding, all but the reserved variables * need to be initialized unless specifically mentioned otherwise. * lzma_lzma_preset() can be used to get a good starting point. * * For raw decoding, both LZMA1 and LZMA2 need dict_size, preset_dict, and * preset_dict_size (if preset_dict != NULL). LZMA1 needs also lc, lp, and pb. */ typedef struct { /** * \brief Dictionary size in bytes * * Dictionary size indicates how many bytes of the recently processed * uncompressed data is kept in memory. One method to reduce size of * the uncompressed data is to store distance-length pairs, which * indicate what data to repeat from the dictionary buffer. Thus, * the bigger the dictionary, the better the compression ratio * usually is. * * Maximum size of the dictionary depends on multiple things: * - Memory usage limit * - Available address space (not a problem on 64-bit systems) * - Selected match finder (encoder only) * * Currently the maximum dictionary size for encoding is 1.5 GiB * (i.e. (UINT32_C(1) << 30) + (UINT32_C(1) << 29)) even on 64-bit * systems for certain match finder implementation reasons. In the * future, there may be match finders that support bigger * dictionaries. * * Decoder already supports dictionaries up to 4 GiB - 1 B (i.e. * UINT32_MAX), so increasing the maximum dictionary size of the * encoder won't cause problems for old decoders. * * Because extremely small dictionaries sizes would have unneeded * overhead in the decoder, the minimum dictionary size is 4096 bytes. * * \note When decoding, too big dictionary does no other harm * than wasting memory. */ uint32_t dict_size; # define LZMA_DICT_SIZE_MIN UINT32_C(4096) # define LZMA_DICT_SIZE_DEFAULT (UINT32_C(1) << 23) /** * \brief Pointer to an initial dictionary * * It is possible to initialize the LZ77 history window using * a preset dictionary. It is useful when compressing many * similar, relatively small chunks of data independently from * each other. The preset dictionary should contain typical * strings that occur in the files being compressed. The most * probable strings should be near the end of the preset dictionary. * * This feature should be used only in special situations. For * now, it works correctly only with raw encoding and decoding. * Currently none of the container formats supported by * liblzma allow preset dictionary when decoding, thus if * you create a .xz or .lzma file with preset dictionary, it * cannot be decoded with the regular decoder functions. In the * future, the .xz format will likely get support for preset * dictionary though. */ const uint8_t *preset_dict; /** * \brief Size of the preset dictionary * * Specifies the size of the preset dictionary. If the size is * bigger than dict_size, only the last dict_size bytes are * processed. * * This variable is read only when preset_dict is not NULL. * If preset_dict is not NULL but preset_dict_size is zero, * no preset dictionary is used (identical to only setting * preset_dict to NULL). */ uint32_t preset_dict_size; /** * \brief Number of literal context bits * * How many of the highest bits of the previous uncompressed * eight-bit byte (also known as `literal') are taken into * account when predicting the bits of the next literal. * * E.g. in typical English text, an upper-case letter is * often followed by a lower-case letter, and a lower-case * letter is usually followed by another lower-case letter. * In the US-ASCII character set, the highest three bits are 010 * for upper-case letters and 011 for lower-case letters. * When lc is at least 3, the literal coding can take advantage of * this property in the uncompressed data. * * There is a limit that applies to literal context bits and literal * position bits together: lc + lp <= 4. Without this limit the * decoding could become very slow, which could have security related * results in some cases like email servers doing virus scanning. * This limit also simplifies the internal implementation in liblzma. * * There may be LZMA1 streams that have lc + lp > 4 (maximum possible * lc would be 8). It is not possible to decode such streams with * liblzma. */ uint32_t lc; # define LZMA_LCLP_MIN 0 # define LZMA_LCLP_MAX 4 # define LZMA_LC_DEFAULT 3 /** * \brief Number of literal position bits * * lp affects what kind of alignment in the uncompressed data is * assumed when encoding literals. A literal is a single 8-bit byte. * See pb below for more information about alignment. */ uint32_t lp; # define LZMA_LP_DEFAULT 0 /** * \brief Number of position bits * * pb affects what kind of alignment in the uncompressed data is * assumed in general. The default means four-byte alignment * (2^ pb =2^2=4), which is often a good choice when there's * no better guess. * * When the aligment is known, setting pb accordingly may reduce * the file size a little. E.g. with text files having one-byte * alignment (US-ASCII, ISO-8859-*, UTF-8), setting pb=0 can * improve compression slightly. For UTF-16 text, pb=1 is a good * choice. If the alignment is an odd number like 3 bytes, pb=0 * might be the best choice. * * Even though the assumed alignment can be adjusted with pb and * lp, LZMA1 and LZMA2 still slightly favor 16-byte alignment. * It might be worth taking into account when designing file formats * that are likely to be often compressed with LZMA1 or LZMA2. */ uint32_t pb; # define LZMA_PB_MIN 0 # define LZMA_PB_MAX 4 # define LZMA_PB_DEFAULT 2 /** Compression mode */ lzma_mode mode; /** * \brief Nice length of a match * * This determines how many bytes the encoder compares from the match * candidates when looking for the best match. Once a match of at * least nice_len bytes long is found, the encoder stops looking for * better candidates and encodes the match. (Naturally, if the found * match is actually longer than nice_len, the actual length is * encoded; it's not truncated to nice_len.) * * Bigger values usually increase the compression ratio and * compression time. For most files, 32 to 128 is a good value, * which gives very good compression ratio at good speed. * * The exact minimum value depends on the match finder. The maximum * is 273, which is the maximum length of a match that LZMA1 and * LZMA2 can encode. */ uint32_t nice_len; /** Match finder ID */ lzma_match_finder mf; /** * \brief Maximum search depth in the match finder * * For every input byte, match finder searches through the hash chain * or binary tree in a loop, each iteration going one step deeper in * the chain or tree. The searching stops if * - a match of at least nice_len bytes long is found; * - all match candidates from the hash chain or binary tree have * been checked; or * - maximum search depth is reached. * * Maximum search depth is needed to prevent the match finder from * wasting too much time in case there are lots of short match * candidates. On the other hand, stopping the search before all * candidates have been checked can reduce compression ratio. * * Setting depth to zero tells liblzma to use an automatic default * value, that depends on the selected match finder and nice_len. * The default is in the range [4, 200] or so (it may vary between * liblzma versions). * * Using a bigger depth value than the default can increase * compression ratio in some cases. There is no strict maximum value, * but high values (thousands or millions) should be used with care: * the encoder could remain fast enough with typical input, but * malicious input could cause the match finder to slow down * dramatically, possibly creating a denial of service attack. */ uint32_t depth; /* * Reserved space to allow possible future extensions without * breaking the ABI. You should not touch these, because the names * of these variables may change. These are and will never be used * with the currently supported options, so it is safe to leave these * uninitialized. */ uint32_t reserved_int1; uint32_t reserved_int2; uint32_t reserved_int3; uint32_t reserved_int4; uint32_t reserved_int5; uint32_t reserved_int6; uint32_t reserved_int7; uint32_t reserved_int8; lzma_reserved_enum reserved_enum1; lzma_reserved_enum reserved_enum2; lzma_reserved_enum reserved_enum3; lzma_reserved_enum reserved_enum4; void *reserved_ptr1; void *reserved_ptr2; } lzma_options_lzma; /** * \brief Set a compression preset to lzma_options_lzma structure * * 0 is the fastest and 9 is the slowest. These match the switches -0 .. -9 * of the xz command line tool. In addition, it is possible to bitwise-or * flags to the preset. Currently only LZMA_PRESET_EXTREME is supported. * The flags are defined in container.h, because the flags are used also * with lzma_easy_encoder(). * * The preset values are subject to changes between liblzma versions. * * This function is available only if LZMA1 or LZMA2 encoder has been enabled * when building liblzma. * * \return On success, false is returned. If the preset is not * supported, true is returned. */ extern LZMA_API(lzma_bool) lzma_lzma_preset( lzma_options_lzma *options, uint32_t preset) lzma_nothrow;
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