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