1 | /* |
2 | * LZMA2 definitions |
3 | * |
4 | * Authors: Lasse Collin <lasse.collin@tukaani.org> |
5 | * Igor Pavlov <https://7-zip.org/> |
6 | * |
7 | * This file has been put into the public domain. |
8 | * You can do whatever you want with this file. |
9 | */ |
10 | |
11 | #ifndef XZ_LZMA2_H |
12 | #define XZ_LZMA2_H |
13 | |
14 | /* Range coder constants */ |
15 | #define RC_SHIFT_BITS 8 |
16 | #define RC_TOP_BITS 24 |
17 | #define RC_TOP_VALUE (1 << RC_TOP_BITS) |
18 | #define RC_BIT_MODEL_TOTAL_BITS 11 |
19 | #define RC_BIT_MODEL_TOTAL (1 << RC_BIT_MODEL_TOTAL_BITS) |
20 | #define RC_MOVE_BITS 5 |
21 | |
22 | /* |
23 | * Maximum number of position states. A position state is the lowest pb |
24 | * number of bits of the current uncompressed offset. In some places there |
25 | * are different sets of probabilities for different position states. |
26 | */ |
27 | #define POS_STATES_MAX (1 << 4) |
28 | |
29 | /* |
30 | * This enum is used to track which LZMA symbols have occurred most recently |
31 | * and in which order. This information is used to predict the next symbol. |
32 | * |
33 | * Symbols: |
34 | * - Literal: One 8-bit byte |
35 | * - Match: Repeat a chunk of data at some distance |
36 | * - Long repeat: Multi-byte match at a recently seen distance |
37 | * - Short repeat: One-byte repeat at a recently seen distance |
38 | * |
39 | * The symbol names are in from STATE_oldest_older_previous. REP means |
40 | * either short or long repeated match, and NONLIT means any non-literal. |
41 | */ |
42 | enum lzma_state { |
43 | STATE_LIT_LIT, |
44 | STATE_MATCH_LIT_LIT, |
45 | STATE_REP_LIT_LIT, |
46 | STATE_SHORTREP_LIT_LIT, |
47 | STATE_MATCH_LIT, |
48 | STATE_REP_LIT, |
49 | STATE_SHORTREP_LIT, |
50 | STATE_LIT_MATCH, |
51 | STATE_LIT_LONGREP, |
52 | STATE_LIT_SHORTREP, |
53 | STATE_NONLIT_MATCH, |
54 | STATE_NONLIT_REP |
55 | }; |
56 | |
57 | /* Total number of states */ |
58 | #define STATES 12 |
59 | |
60 | /* The lowest 7 states indicate that the previous state was a literal. */ |
61 | #define LIT_STATES 7 |
62 | |
63 | /* Indicate that the latest symbol was a literal. */ |
64 | static inline void lzma_state_literal(enum lzma_state *state) |
65 | { |
66 | if (*state <= STATE_SHORTREP_LIT_LIT) |
67 | *state = STATE_LIT_LIT; |
68 | else if (*state <= STATE_LIT_SHORTREP) |
69 | *state -= 3; |
70 | else |
71 | *state -= 6; |
72 | } |
73 | |
74 | /* Indicate that the latest symbol was a match. */ |
75 | static inline void lzma_state_match(enum lzma_state *state) |
76 | { |
77 | *state = *state < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH; |
78 | } |
79 | |
80 | /* Indicate that the latest state was a long repeated match. */ |
81 | static inline void lzma_state_long_rep(enum lzma_state *state) |
82 | { |
83 | *state = *state < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP; |
84 | } |
85 | |
86 | /* Indicate that the latest symbol was a short match. */ |
87 | static inline void lzma_state_short_rep(enum lzma_state *state) |
88 | { |
89 | *state = *state < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP; |
90 | } |
91 | |
92 | /* Test if the previous symbol was a literal. */ |
93 | static inline bool lzma_state_is_literal(enum lzma_state state) |
94 | { |
95 | return state < LIT_STATES; |
96 | } |
97 | |
98 | /* Each literal coder is divided in three sections: |
99 | * - 0x001-0x0FF: Without match byte |
100 | * - 0x101-0x1FF: With match byte; match bit is 0 |
101 | * - 0x201-0x2FF: With match byte; match bit is 1 |
102 | * |
103 | * Match byte is used when the previous LZMA symbol was something else than |
104 | * a literal (that is, it was some kind of match). |
105 | */ |
106 | #define LITERAL_CODER_SIZE 0x300 |
107 | |
108 | /* Maximum number of literal coders */ |
109 | #define LITERAL_CODERS_MAX (1 << 4) |
110 | |
111 | /* Minimum length of a match is two bytes. */ |
112 | #define MATCH_LEN_MIN 2 |
113 | |
114 | /* Match length is encoded with 4, 5, or 10 bits. |
115 | * |
116 | * Length Bits |
117 | * 2-9 4 = Choice=0 + 3 bits |
118 | * 10-17 5 = Choice=1 + Choice2=0 + 3 bits |
119 | * 18-273 10 = Choice=1 + Choice2=1 + 8 bits |
120 | */ |
121 | #define LEN_LOW_BITS 3 |
122 | #define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS) |
123 | #define LEN_MID_BITS 3 |
124 | #define LEN_MID_SYMBOLS (1 << LEN_MID_BITS) |
125 | #define LEN_HIGH_BITS 8 |
126 | #define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS) |
127 | #define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS) |
128 | |
129 | /* |
130 | * Maximum length of a match is 273 which is a result of the encoding |
131 | * described above. |
132 | */ |
133 | #define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1) |
134 | |
135 | /* |
136 | * Different sets of probabilities are used for match distances that have |
137 | * very short match length: Lengths of 2, 3, and 4 bytes have a separate |
138 | * set of probabilities for each length. The matches with longer length |
139 | * use a shared set of probabilities. |
140 | */ |
141 | #define DIST_STATES 4 |
142 | |
143 | /* |
144 | * Get the index of the appropriate probability array for decoding |
145 | * the distance slot. |
146 | */ |
147 | static inline uint32_t lzma_get_dist_state(uint32_t len) |
148 | { |
149 | return len < DIST_STATES + MATCH_LEN_MIN |
150 | ? len - MATCH_LEN_MIN : DIST_STATES - 1; |
151 | } |
152 | |
153 | /* |
154 | * The highest two bits of a 32-bit match distance are encoded using six bits. |
155 | * This six-bit value is called a distance slot. This way encoding a 32-bit |
156 | * value takes 6-36 bits, larger values taking more bits. |
157 | */ |
158 | #define DIST_SLOT_BITS 6 |
159 | #define DIST_SLOTS (1 << DIST_SLOT_BITS) |
160 | |
161 | /* Match distances up to 127 are fully encoded using probabilities. Since |
162 | * the highest two bits (distance slot) are always encoded using six bits, |
163 | * the distances 0-3 don't need any additional bits to encode, since the |
164 | * distance slot itself is the same as the actual distance. DIST_MODEL_START |
165 | * indicates the first distance slot where at least one additional bit is |
166 | * needed. |
167 | */ |
168 | #define DIST_MODEL_START 4 |
169 | |
170 | /* |
171 | * Match distances greater than 127 are encoded in three pieces: |
172 | * - distance slot: the highest two bits |
173 | * - direct bits: 2-26 bits below the highest two bits |
174 | * - alignment bits: four lowest bits |
175 | * |
176 | * Direct bits don't use any probabilities. |
177 | * |
178 | * The distance slot value of 14 is for distances 128-191. |
179 | */ |
180 | #define DIST_MODEL_END 14 |
181 | |
182 | /* Distance slots that indicate a distance <= 127. */ |
183 | #define FULL_DISTANCES_BITS (DIST_MODEL_END / 2) |
184 | #define FULL_DISTANCES (1 << FULL_DISTANCES_BITS) |
185 | |
186 | /* |
187 | * For match distances greater than 127, only the highest two bits and the |
188 | * lowest four bits (alignment) is encoded using probabilities. |
189 | */ |
190 | #define ALIGN_BITS 4 |
191 | #define ALIGN_SIZE (1 << ALIGN_BITS) |
192 | #define ALIGN_MASK (ALIGN_SIZE - 1) |
193 | |
194 | /* Total number of all probability variables */ |
195 | #define PROBS_TOTAL (1846 + LITERAL_CODERS_MAX * LITERAL_CODER_SIZE) |
196 | |
197 | /* |
198 | * LZMA remembers the four most recent match distances. Reusing these |
199 | * distances tends to take less space than re-encoding the actual |
200 | * distance value. |
201 | */ |
202 | #define REPS 4 |
203 | |
204 | #endif |
205 | |