204 lines
6 KiB
C
204 lines
6 KiB
C
/*
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* LZMA2 definitions
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*
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* Authors: Lasse Collin <lasse.collin@tukaani.org>
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* Igor Pavlov <http://7-zip.org/>
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*
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* This file has been put into the public domain.
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* You can do whatever you want with this file.
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*/
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#ifndef XZ_LZMA2_H
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#define XZ_LZMA2_H
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/* Range coder constants */
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#define RC_SHIFT_BITS 8
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#define RC_TOP_BITS 24
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#define RC_TOP_VALUE (1 << RC_TOP_BITS)
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#define RC_BIT_MODEL_TOTAL_BITS 11
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#define RC_BIT_MODEL_TOTAL (1 << RC_BIT_MODEL_TOTAL_BITS)
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#define RC_MOVE_BITS 5
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/*
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* Maximum number of position states. A position state is the lowest pb
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* number of bits of the current uncompressed offset. In some places there
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* are different sets of probabilities for different position states.
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*/
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#define POS_STATES_MAX (1 << 4)
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/*
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* This enum is used to track which LZMA symbols have occurred most recently
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* and in which order. This information is used to predict the next symbol.
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*
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* Symbols:
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* - Literal: One 8-bit byte
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* - Match: Repeat a chunk of data at some distance
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* - Long repeat: Multi-byte match at a recently seen distance
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* - Short repeat: One-byte repeat at a recently seen distance
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*
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* The symbol names are in from STATE_oldest_older_previous. REP means
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* either short or long repeated match, and NONLIT means any non-literal.
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*/
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enum lzma_state {
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STATE_LIT_LIT,
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STATE_MATCH_LIT_LIT,
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STATE_REP_LIT_LIT,
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STATE_SHORTREP_LIT_LIT,
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STATE_MATCH_LIT,
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STATE_REP_LIT,
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STATE_SHORTREP_LIT,
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STATE_LIT_MATCH,
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STATE_LIT_LONGREP,
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STATE_LIT_SHORTREP,
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STATE_NONLIT_MATCH,
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STATE_NONLIT_REP
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};
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/* Total number of states */
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#define STATES 12
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/* The lowest 7 states indicate that the previous state was a literal. */
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#define LIT_STATES 7
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/* Indicate that the latest symbol was a literal. */
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static inline void lzma_state_literal(enum lzma_state *state)
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{
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if (*state <= STATE_SHORTREP_LIT_LIT)
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*state = STATE_LIT_LIT;
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else if (*state <= STATE_LIT_SHORTREP)
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*state -= 3;
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else
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*state -= 6;
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}
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/* Indicate that the latest symbol was a match. */
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static inline void lzma_state_match(enum lzma_state *state)
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{
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*state = *state < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH;
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}
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/* Indicate that the latest state was a long repeated match. */
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static inline void lzma_state_long_rep(enum lzma_state *state)
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{
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*state = *state < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP;
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}
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/* Indicate that the latest symbol was a short match. */
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static inline void lzma_state_short_rep(enum lzma_state *state)
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{
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*state = *state < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP;
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}
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/* Test if the previous symbol was a literal. */
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static inline bool lzma_state_is_literal(enum lzma_state state)
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{
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return state < LIT_STATES;
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}
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/* Each literal coder is divided in three sections:
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* - 0x001-0x0FF: Without match byte
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* - 0x101-0x1FF: With match byte; match bit is 0
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* - 0x201-0x2FF: With match byte; match bit is 1
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*
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* Match byte is used when the previous LZMA symbol was something else than
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* a literal (that is, it was some kind of match).
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*/
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#define LITERAL_CODER_SIZE 0x300
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/* Maximum number of literal coders */
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#define LITERAL_CODERS_MAX (1 << 4)
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/* Minimum length of a match is two bytes. */
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#define MATCH_LEN_MIN 2
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/* Match length is encoded with 4, 5, or 10 bits.
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*
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* Length Bits
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* 2-9 4 = Choice=0 + 3 bits
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* 10-17 5 = Choice=1 + Choice2=0 + 3 bits
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* 18-273 10 = Choice=1 + Choice2=1 + 8 bits
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*/
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#define LEN_LOW_BITS 3
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#define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS)
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#define LEN_MID_BITS 3
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#define LEN_MID_SYMBOLS (1 << LEN_MID_BITS)
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#define LEN_HIGH_BITS 8
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#define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS)
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#define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS)
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/*
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* Maximum length of a match is 273 which is a result of the encoding
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* described above.
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*/
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#define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1)
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/*
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* Different sets of probabilities are used for match distances that have
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* very short match length: Lengths of 2, 3, and 4 bytes have a separate
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* set of probabilities for each length. The matches with longer length
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* use a shared set of probabilities.
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*/
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#define DIST_STATES 4
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/*
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* Get the index of the appropriate probability array for decoding
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* the distance slot.
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*/
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static inline uint32_t lzma_get_dist_state(uint32_t len)
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{
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return len < DIST_STATES + MATCH_LEN_MIN
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? len - MATCH_LEN_MIN : DIST_STATES - 1;
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}
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/*
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* The highest two bits of a 32-bit match distance are encoded using six bits.
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* This six-bit value is called a distance slot. This way encoding a 32-bit
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* value takes 6-36 bits, larger values taking more bits.
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*/
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#define DIST_SLOT_BITS 6
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#define DIST_SLOTS (1 << DIST_SLOT_BITS)
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/* Match distances up to 127 are fully encoded using probabilities. Since
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* the highest two bits (distance slot) are always encoded using six bits,
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* the distances 0-3 don't need any additional bits to encode, since the
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* distance slot itself is the same as the actual distance. DIST_MODEL_START
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* indicates the first distance slot where at least one additional bit is
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* needed.
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*/
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#define DIST_MODEL_START 4
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/*
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* Match distances greater than 127 are encoded in three pieces:
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* - distance slot: the highest two bits
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* - direct bits: 2-26 bits below the highest two bits
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* - alignment bits: four lowest bits
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*
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* Direct bits don't use any probabilities.
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*
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* The distance slot value of 14 is for distances 128-191.
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*/
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#define DIST_MODEL_END 14
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/* Distance slots that indicate a distance <= 127. */
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#define FULL_DISTANCES_BITS (DIST_MODEL_END / 2)
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#define FULL_DISTANCES (1 << FULL_DISTANCES_BITS)
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/*
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* For match distances greater than 127, only the highest two bits and the
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* lowest four bits (alignment) is encoded using probabilities.
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*/
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#define ALIGN_BITS 4
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#define ALIGN_SIZE (1 << ALIGN_BITS)
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#define ALIGN_MASK (ALIGN_SIZE - 1)
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/* Total number of all probability variables */
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#define PROBS_TOTAL (1846 + LITERAL_CODERS_MAX * LITERAL_CODER_SIZE)
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/*
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* LZMA remembers the four most recent match distances. Reusing these
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* distances tends to take less space than re-encoding the actual
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* distance value.
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*/
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#define REPS 4
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#endif
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