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