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DEFINITIONS
This source file includes following definitions.
- LZMA_API
- LZMA_API
/**
* \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.
*/
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;