1 | /*
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2 | * RangeEncoder
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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 | package org.tukaani.xz.rangecoder;
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12 |
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13 | import java.io.IOException;
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14 |
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15 | public abstract class RangeEncoder extends RangeCoder {
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16 | private static final int MOVE_REDUCING_BITS = 4;
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17 | private static final int BIT_PRICE_SHIFT_BITS = 4;
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18 |
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19 | private static final int[] prices
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20 | = new int[BIT_MODEL_TOTAL >>> MOVE_REDUCING_BITS];
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21 |
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22 | private long low;
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23 | private int range;
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24 |
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25 | // NOTE: int is OK for LZMA2 because a compressed chunk
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26 | // is not more than 64 KiB, but with LZMA1 there is no chunking
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27 | // so in theory cacheSize can grow very big. To be very safe,
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28 | // use long instead of int since this code is used for LZMA1 too.
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29 | long cacheSize;
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30 | private byte cache;
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31 |
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32 | static {
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33 | for (int i = (1 << MOVE_REDUCING_BITS) / 2; i < BIT_MODEL_TOTAL;
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34 | i += (1 << MOVE_REDUCING_BITS)) {
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35 | int w = i;
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36 | int bitCount = 0;
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37 |
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38 | for (int j = 0; j < BIT_PRICE_SHIFT_BITS; ++j) {
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39 | w *= w;
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40 | bitCount <<= 1;
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41 |
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42 | while ((w & 0xFFFF0000) != 0) {
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43 | w >>>= 1;
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44 | ++bitCount;
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45 | }
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46 | }
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47 |
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48 | prices[i >> MOVE_REDUCING_BITS]
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49 | = (BIT_MODEL_TOTAL_BITS << BIT_PRICE_SHIFT_BITS)
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50 | - 15 - bitCount;
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51 | }
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52 | }
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53 |
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54 | public void reset() {
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55 | low = 0;
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56 | range = 0xFFFFFFFF;
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57 | cache = 0x00;
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58 | cacheSize = 1;
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59 | }
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60 |
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61 | public int getPendingSize() {
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62 | // This function is only needed by users of RangeEncoderToBuffer,
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63 | // but providing a must-be-never-called version here makes
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64 | // LZMAEncoder simpler.
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65 | throw new Error();
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66 | }
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67 |
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68 | public int finish() throws IOException {
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69 | for (int i = 0; i < 5; ++i)
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70 | shiftLow();
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71 |
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72 | // RangeEncoderToBuffer.finish() needs a return value to tell
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73 | // how big the finished buffer is. RangeEncoderToStream has no
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74 | // buffer and thus no return value is needed. Here we use a dummy
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75 | // value which can be overriden in RangeEncoderToBuffer.finish().
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76 | return -1;
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77 | }
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78 |
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79 | abstract void writeByte(int b) throws IOException;
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80 |
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81 | private void shiftLow() throws IOException {
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82 | int lowHi = (int)(low >>> 32);
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83 |
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84 | if (lowHi != 0 || low < 0xFF000000L) {
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85 | int temp = cache;
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86 |
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87 | do {
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88 | writeByte(temp + lowHi);
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89 | temp = 0xFF;
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90 | } while (--cacheSize != 0);
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91 |
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92 | cache = (byte)(low >>> 24);
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93 | }
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94 |
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95 | ++cacheSize;
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96 | low = (low & 0x00FFFFFF) << 8;
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97 | }
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98 |
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99 | public void encodeBit(short[] probs, int index, int bit)
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100 | throws IOException {
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101 | int prob = probs[index];
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102 | int bound = (range >>> BIT_MODEL_TOTAL_BITS) * prob;
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103 |
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104 | // NOTE: Any non-zero value for bit is taken as 1.
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105 | if (bit == 0) {
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106 | range = bound;
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107 | probs[index] = (short)(
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108 | prob + ((BIT_MODEL_TOTAL - prob) >>> MOVE_BITS));
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109 | } else {
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110 | low += bound & 0xFFFFFFFFL;
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111 | range -= bound;
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112 | probs[index] = (short)(prob - (prob >>> MOVE_BITS));
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113 | }
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114 |
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115 | if ((range & TOP_MASK) == 0) {
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116 | range <<= SHIFT_BITS;
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117 | shiftLow();
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118 | }
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119 | }
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120 |
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121 | public static int getBitPrice(int prob, int bit) {
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122 | // NOTE: Unlike in encodeBit(), here bit must be 0 or 1.
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123 | assert bit == 0 || bit == 1;
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124 | return prices[(prob ^ ((-bit) & (BIT_MODEL_TOTAL - 1)))
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125 | >>> MOVE_REDUCING_BITS];
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126 | }
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127 |
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128 | public void encodeBitTree(short[] probs, int symbol) throws IOException {
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129 | int index = 1;
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130 | int mask = probs.length;
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131 |
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132 | do {
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133 | mask >>>= 1;
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134 | int bit = symbol & mask;
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135 | encodeBit(probs, index, bit);
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136 |
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137 | index <<= 1;
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138 | if (bit != 0)
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139 | index |= 1;
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140 |
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141 | } while (mask != 1);
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142 | }
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143 |
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144 | public static int getBitTreePrice(short[] probs, int symbol) {
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145 | int price = 0;
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146 | symbol |= probs.length;
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147 |
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148 | do {
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149 | int bit = symbol & 1;
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150 | symbol >>>= 1;
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151 | price += getBitPrice(probs[symbol], bit);
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152 | } while (symbol != 1);
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153 |
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154 | return price;
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155 | }
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156 |
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157 | public void encodeReverseBitTree(short[] probs, int symbol)
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158 | throws IOException {
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159 | int index = 1;
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160 | symbol |= probs.length;
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161 |
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162 | do {
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163 | int bit = symbol & 1;
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164 | symbol >>>= 1;
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165 | encodeBit(probs, index, bit);
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166 | index = (index << 1) | bit;
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167 | } while (symbol != 1);
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168 | }
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169 |
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170 | public static int getReverseBitTreePrice(short[] probs, int symbol) {
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171 | int price = 0;
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172 | int index = 1;
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173 | symbol |= probs.length;
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174 |
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175 | do {
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176 | int bit = symbol & 1;
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177 | symbol >>>= 1;
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178 | price += getBitPrice(probs[index], bit);
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179 | index = (index << 1) | bit;
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180 | } while (symbol != 1);
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181 |
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182 | return price;
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183 | }
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184 |
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185 | public void encodeDirectBits(int value, int count) throws IOException {
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186 | do {
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187 | range >>>= 1;
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188 | low += range & (0 - ((value >>> --count) & 1));
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189 |
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190 | if ((range & TOP_MASK) == 0) {
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191 | range <<= SHIFT_BITS;
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192 | shiftLow();
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193 | }
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194 | } while (count != 0);
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195 | }
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196 |
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197 | public static int getDirectBitsPrice(int count) {
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198 | return count << BIT_PRICE_SHIFT_BITS;
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199 | }
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200 | }
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