1// SPDX-License-Identifier: 0BSD 2 3/////////////////////////////////////////////////////////////////////////////// 4// 5/// \file lzma_common.h 6/// \brief Private definitions common to LZMA encoder and decoder 7/// 8// Authors: Igor Pavlov 9// Lasse Collin 10// 11/////////////////////////////////////////////////////////////////////////////// 12 13#ifndef LZMA_LZMA_COMMON_H 14#define LZMA_LZMA_COMMON_H 15 16#include "common.h" 17#include "range_common.h" 18 19 20/////////////////// 21// Miscellaneous // 22/////////////////// 23 24/// Maximum number of position states. A position state is the lowest pos bits 25/// number of bits of the current uncompressed offset. In some places there 26/// are different sets of probabilities for different pos states. 27#define POS_STATES_MAX (1 << LZMA_PB_MAX) 28 29 30/// Validates lc, lp, and pb. 31static inline bool 32is_lclppb_valid(const lzma_options_lzma *options) 33{ 34 return options->lc <= LZMA_LCLP_MAX && options->lp <= LZMA_LCLP_MAX 35 && options->lc + options->lp <= LZMA_LCLP_MAX 36 && options->pb <= LZMA_PB_MAX; 37} 38 39 40/////////// 41// State // 42/////////// 43 44/// This enum is used to track which events have occurred most recently and 45/// in which order. This information is used to predict the next event. 46/// 47/// Events: 48/// - Literal: One 8-bit byte 49/// - Match: Repeat a chunk of data at some distance 50/// - Long repeat: Multi-byte match at a recently seen distance 51/// - Short repeat: One-byte repeat at a recently seen distance 52/// 53/// The event names are in from STATE_oldest_older_previous. REP means 54/// either short or long repeated match, and NONLIT means any non-literal. 55typedef enum { 56 STATE_LIT_LIT, 57 STATE_MATCH_LIT_LIT, 58 STATE_REP_LIT_LIT, 59 STATE_SHORTREP_LIT_LIT, 60 STATE_MATCH_LIT, 61 STATE_REP_LIT, 62 STATE_SHORTREP_LIT, 63 STATE_LIT_MATCH, 64 STATE_LIT_LONGREP, 65 STATE_LIT_SHORTREP, 66 STATE_NONLIT_MATCH, 67 STATE_NONLIT_REP, 68} lzma_lzma_state; 69 70 71/// Total number of states 72#define STATES 12 73 74/// The lowest 7 states indicate that the previous state was a literal. 75#define LIT_STATES 7 76 77 78/// Indicate that the latest state was a literal. 79#define update_literal(state) \ 80 state = ((state) <= STATE_SHORTREP_LIT_LIT \ 81 ? STATE_LIT_LIT \ 82 : ((state) <= STATE_LIT_SHORTREP \ 83 ? (state) - 3 \ 84 : (state) - 6)) 85 86/// Like update_literal(state) but when it is already known that 87/// is_literal_state(state) is true. 88#define update_literal_normal(state) \ 89 state = ((state) <= STATE_SHORTREP_LIT_LIT \ 90 ? STATE_LIT_LIT \ 91 : (state) - 3); 92 93/// Like update_literal(state) but when it is already known that 94/// is_literal_state(state) is false. 95#define update_literal_matched(state) \ 96 state = ((state) <= STATE_LIT_SHORTREP \ 97 ? (state) - 3 \ 98 : (state) - 6); 99 100/// Indicate that the latest state was a match. 101#define update_match(state) \ 102 state = ((state) < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH) 103 104/// Indicate that the latest state was a long repeated match. 105#define update_long_rep(state) \ 106 state = ((state) < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP) 107 108/// Indicate that the latest state was a short match. 109#define update_short_rep(state) \ 110 state = ((state) < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP) 111 112/// Test if the previous state was a literal. 113#define is_literal_state(state) \ 114 ((state) < LIT_STATES) 115 116 117///////////// 118// Literal // 119///////////// 120 121/// Each literal coder is divided in three sections: 122/// - 0x001-0x0FF: Without match byte 123/// - 0x101-0x1FF: With match byte; match bit is 0 124/// - 0x201-0x2FF: With match byte; match bit is 1 125/// 126/// Match byte is used when the previous LZMA symbol was something else than 127/// a literal (that is, it was some kind of match). 128#define LITERAL_CODER_SIZE UINT32_C(0x300) 129 130/// Maximum number of literal coders 131#define LITERAL_CODERS_MAX (1 << LZMA_LCLP_MAX) 132 133/// Calculates the literal_mask that literal_subcoder() needs. 134#define literal_mask_calc(lc, lp) \ 135 ((UINT32_C(0x100) << (lp)) - (UINT32_C(0x100) >> (lc))) 136 137/// Locate the literal coder for the next literal byte. The choice depends on 138/// - the lowest literal_pos_bits bits of the position of the current 139/// byte; and 140/// - the highest literal_context_bits bits of the previous byte. 141#define literal_subcoder(probs, lc, literal_mask, pos, prev_byte) \ 142 ((probs) + UINT32_C(3) * \ 143 (((((pos) << 8) + (prev_byte)) & (literal_mask)) << (lc))) 144 145 146static inline void 147literal_init(probability *probs, uint32_t lc, uint32_t lp) 148{ 149 assert(lc + lp <= LZMA_LCLP_MAX); 150 151 const size_t coders = LITERAL_CODER_SIZE << (lc + lp); 152 153 for (size_t i = 0; i < coders; ++i) 154 bit_reset(probs[i]); 155 156 return; 157} 158 159 160////////////////// 161// Match length // 162////////////////// 163 164// Minimum length of a match is two bytes. 165#define MATCH_LEN_MIN 2 166 167// Match length is encoded with 4, 5, or 10 bits. 168// 169// Length Bits 170// 2-9 4 = Choice=0 + 3 bits 171// 10-17 5 = Choice=1 + Choice2=0 + 3 bits 172// 18-273 10 = Choice=1 + Choice2=1 + 8 bits 173#define LEN_LOW_BITS 3 174#define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS) 175#define LEN_MID_BITS 3 176#define LEN_MID_SYMBOLS (1 << LEN_MID_BITS) 177#define LEN_HIGH_BITS 8 178#define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS) 179#define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS) 180 181// Maximum length of a match is 273 which is a result of the encoding 182// described above. 183#define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1) 184 185 186//////////////////// 187// Match distance // 188//////////////////// 189 190// Different sets of probabilities are used for match distances that have very 191// short match length: Lengths of 2, 3, and 4 bytes have a separate set of 192// probabilities for each length. The matches with longer length use a shared 193// set of probabilities. 194#define DIST_STATES 4 195 196// Macro to get the index of the appropriate probability array. 197#define get_dist_state(len) \ 198 ((len) < DIST_STATES + MATCH_LEN_MIN \ 199 ? (len) - MATCH_LEN_MIN \ 200 : DIST_STATES - 1) 201 202// The highest two bits of a match distance (distance slot) are encoded 203// using six bits. See fastpos.h for more explanation. 204#define DIST_SLOT_BITS 6 205#define DIST_SLOTS (1 << DIST_SLOT_BITS) 206 207// Match distances up to 127 are fully encoded using probabilities. Since 208// the highest two bits (distance slot) are always encoded using six bits, 209// the distances 0-3 don't need any additional bits to encode, since the 210// distance slot itself is the same as the actual distance. DIST_MODEL_START 211// indicates the first distance slot where at least one additional bit is 212// needed. 213#define DIST_MODEL_START 4 214 215// Match distances greater than 127 are encoded in three pieces: 216// - distance slot: the highest two bits 217// - direct bits: 2-26 bits below the highest two bits 218// - alignment bits: four lowest bits 219// 220// Direct bits don't use any probabilities. 221// 222// The distance slot value of 14 is for distances 128-191 (see the table in 223// fastpos.h to understand why). 224#define DIST_MODEL_END 14 225 226// Distance slots that indicate a distance <= 127. 227#define FULL_DISTANCES_BITS (DIST_MODEL_END / 2) 228#define FULL_DISTANCES (1 << FULL_DISTANCES_BITS) 229 230// For match distances greater than 127, only the highest two bits and the 231// lowest four bits (alignment) is encoded using probabilities. 232#define ALIGN_BITS 4 233#define ALIGN_SIZE (1 << ALIGN_BITS) 234#define ALIGN_MASK (ALIGN_SIZE - 1) 235 236// LZMA remembers the four most recent match distances. Reusing these distances 237// tends to take less space than re-encoding the actual distance value. 238#define REPS 4 239 240#endif 241