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[xz/debian.git] / src / liblzma / api / lzma / 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;