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204 lines
6.0 KiB
204 lines
6.0 KiB
/* |
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* LZMA2 definitions |
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* |
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* Authors: Lasse Collin <[email protected]> |
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* Igor Pavlov <https://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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