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annotate src/com/jcraft/jzlib/CRC32.java @ 387:04a0316bbfe3

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author Carl Byington <carl@five-ten-sg.com>
date Wed, 06 Aug 2014 11:50:58 -0700
parents 46c2115ae1c8
children
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357
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1 /* -*-mode:java; c-basic-offset:2; -*- */
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2 /*
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3 Copyright (c) 2011 ymnk, JCraft,Inc. All rights reserved.
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4
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5 Redistribution and use in source and binary forms, with or without
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6 modification, are permitted provided that the following conditions are met:
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7
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8 1. Redistributions of source code must retain the above copyright notice,
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9 this list of conditions and the following disclaimer.
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10
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11 2. Redistributions in binary form must reproduce the above copyright
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12 notice, this list of conditions and the following disclaimer in
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13 the documentation and/or other materials provided with the distribution.
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14
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15 3. The names of the authors may not be used to endorse or promote products
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16 derived from this software without specific prior written permission.
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17
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18 THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
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19 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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20 FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JCRAFT,
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21 INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT, INDIRECT,
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22 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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23 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
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24 OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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25 LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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26 NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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27 EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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28 */
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29 /*
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30 * This program is based on zlib-1.1.3, so all credit should go authors
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31 * Jean-loup Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu)
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32 * and contributors of zlib.
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33 */
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34
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35 package com.jcraft.jzlib;
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36
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37 final public class CRC32 implements Checksum {
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38
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39 /*
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40 * The following logic has come from RFC1952.
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41 */
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42 private int v = 0;
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43 private static int[] crc_table = null;
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44 static {
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45 crc_table = new int[256];
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46 for (int n = 0; n < 256; n++) {
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47 int c = n;
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48 for (int k = 8; --k >= 0; ) {
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49 if ((c & 1) != 0)
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50 c = 0xedb88320 ^ (c >>> 1);
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51 else
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52 c = c >>> 1;
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53 }
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54 crc_table[n] = c;
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55 }
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56 }
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57
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58 public void update (byte[] buf, int index, int len) {
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59 int c = ~v;
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60 while (--len >= 0)
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61 c = crc_table[(c^buf[index++])&0xff]^(c >>> 8);
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62 v = ~c;
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63 }
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64
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65 public void reset(){
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66 v = 0;
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67 }
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68
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69 public void reset(long vv){
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70 v = (int)(vv&0xffffffffL);
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71 }
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72
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73 public long getValue(){
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74 return (long)(v&0xffffffffL);
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75 }
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76
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77 // The following logic has come from zlib.1.2.
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78 private static final int GF2_DIM = 32;
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79 static long combine(long crc1, long crc2, long len2){
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80 long row;
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81 long[] even = new long[GF2_DIM];
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82 long[] odd = new long[GF2_DIM];
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83
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84 // degenerate case (also disallow negative lengths)
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85 if (len2 <= 0)
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86 return crc1;
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87
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88 // put operator for one zero bit in odd
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89 odd[0] = 0xedb88320L; // CRC-32 polynomial
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90 row = 1;
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91 for (int n = 1; n < GF2_DIM; n++) {
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92 odd[n] = row;
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93 row <<= 1;
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94 }
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95
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96 // put operator for two zero bits in even
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97 gf2_matrix_square(even, odd);
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98
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99 // put operator for four zero bits in odd
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100 gf2_matrix_square(odd, even);
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101
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102 // apply len2 zeros to crc1 (first square will put the operator for one
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103 // zero byte, eight zero bits, in even)
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104 do {
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105 // apply zeros operator for this bit of len2
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106 gf2_matrix_square(even, odd);
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107 if ((len2 & 1)!=0)
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108 crc1 = gf2_matrix_times(even, crc1);
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109 len2 >>= 1;
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110
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111 // if no more bits set, then done
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112 if (len2 == 0)
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113 break;
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114
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115 // another iteration of the loop with odd and even swapped
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116 gf2_matrix_square(odd, even);
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117 if ((len2 & 1)!=0)
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118 crc1 = gf2_matrix_times(odd, crc1);
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119 len2 >>= 1;
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120
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121 // if no more bits set, then done
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122 } while (len2 != 0);
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123
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124 /* return combined crc */
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125 crc1 ^= crc2;
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126 return crc1;
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127 }
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128
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129 private static long gf2_matrix_times(long[] mat, long vec){
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130 long sum = 0;
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131 int index = 0;
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132 while (vec!=0) {
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133 if ((vec & 1)!=0)
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134 sum ^= mat[index];
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135 vec >>= 1;
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136 index++;
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137 }
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138 return sum;
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139 }
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140
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141 static final void gf2_matrix_square(long[] square, long[] mat) {
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142 for (int n = 0; n < GF2_DIM; n++)
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143 square[n] = gf2_matrix_times(mat, mat[n]);
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144 }
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145
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146 /*
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147 private java.util.zip.CRC32 crc32 = new java.util.zip.CRC32();
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148
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149 public void update(byte[] buf, int index, int len){
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150 if(buf==null) {crc32.reset();}
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151 else{crc32.update(buf, index, len);}
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152 }
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153 public void reset(){
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154 crc32.reset();
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155 }
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156 public void reset(long init){
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157 if(init==0L){
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158 crc32.reset();
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159 }
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160 else{
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161 System.err.println("unsupported operation");
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162 }
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163 }
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164 public long getValue(){
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165 return crc32.getValue();
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166 }
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167 */
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168 public CRC32 copy(){
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169 CRC32 foo = new CRC32();
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170 foo.v = this.v;
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171 return foo;
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172 }
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173
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174 public static int[] getCRC32Table(){
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175 int[] tmp = new int[crc_table.length];
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176 System.arraycopy(crc_table, 0, tmp, 0, tmp.length);
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177 return tmp;
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178 }
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179 }