src/liblzma/api/lzma/lzma.h

/**
 * \file        lzma/lzma.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.
	 */
	void *reserved_ptr1;
	void *reserved_ptr2;
	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;

} 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.
 */
extern LZMA_API(lzma_bool) lzma_lzma_preset(
		lzma_options_lzma *options, uint32_t preset) lzma_nothrow;