1 | /** |
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2 | * Copyright 2007 The Apache Software Foundation |
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3 | * |
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4 | * Licensed to the Apache Software Foundation (ASF) under one |
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5 | * or more contributor license agreements. See the NOTICE file |
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6 | * distributed with this work for additional information |
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7 | * regarding copyright ownership. The ASF licenses this file |
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8 | * to you under the Apache License, Version 2.0 (the |
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9 | * "License"); you may not use this file except in compliance |
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10 | * with the License. You may obtain a copy of the License at |
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11 | * |
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12 | * http://www.apache.org/licenses/LICENSE-2.0 |
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13 | * |
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14 | * Unless required by applicable law or agreed to in writing, software |
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15 | * distributed under the License is distributed on an "AS IS" BASIS, |
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16 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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17 | * See the License for the specific language governing permissions and |
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18 | * limitations under the License. |
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19 | */ |
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20 | |
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21 | package org.apache.hadoop.util.hash; |
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22 | |
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23 | import java.io.FileInputStream; |
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24 | import java.io.IOException; |
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25 | |
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26 | /** |
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27 | * Produces 32-bit hash for hash table lookup. |
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28 | * |
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29 | * <pre>lookup3.c, by Bob Jenkins, May 2006, Public Domain. |
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30 | * |
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31 | * You can use this free for any purpose. It's in the public domain. |
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32 | * It has no warranty. |
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33 | * </pre> |
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34 | * |
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35 | * @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a> |
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36 | * @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this |
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37 | * function compares to others such as CRC, MD?, etc</a> |
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38 | * @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the |
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39 | * Dr. Dobbs Article</a> |
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40 | */ |
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41 | public class JenkinsHash extends Hash { |
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42 | private static long INT_MASK = 0x00000000ffffffffL; |
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43 | private static long BYTE_MASK = 0x00000000000000ffL; |
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44 | |
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45 | private static JenkinsHash _instance = new JenkinsHash(); |
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46 | |
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47 | public static Hash getInstance() { |
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48 | return _instance; |
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49 | } |
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50 | |
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51 | private static long rot(long val, int pos) { |
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52 | return ((Integer.rotateLeft( |
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53 | (int)(val & INT_MASK), pos)) & INT_MASK); |
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54 | } |
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55 | |
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56 | /** |
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57 | * taken from hashlittle() -- hash a variable-length key into a 32-bit value |
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58 | * |
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59 | * @param key the key (the unaligned variable-length array of bytes) |
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60 | * @param nbytes number of bytes to include in hash |
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61 | * @param initval can be any integer value |
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62 | * @return a 32-bit value. Every bit of the key affects every bit of the |
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63 | * return value. Two keys differing by one or two bits will have totally |
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64 | * different hash values. |
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65 | * |
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66 | * <p>The best hash table sizes are powers of 2. There is no need to do mod |
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67 | * a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. |
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68 | * For example, if you need only 10 bits, do |
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69 | * <code>h = (h & hashmask(10));</code> |
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70 | * In which case, the hash table should have hashsize(10) elements. |
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71 | * |
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72 | * <p>If you are hashing n strings byte[][] k, do it like this: |
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73 | * for (int i = 0, h = 0; i < n; ++i) h = hash( k[i], h); |
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74 | * |
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75 | * <p>By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this |
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76 | * code any way you wish, private, educational, or commercial. It's free. |
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77 | * |
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78 | * <p>Use for hash table lookup, or anything where one collision in 2^^32 is |
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79 | * acceptable. Do NOT use for cryptographic purposes. |
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80 | */ |
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81 | @SuppressWarnings("fallthrough") |
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82 | public int hash(byte[] key, int nbytes, int initval) { |
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83 | int length = nbytes; |
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84 | long a, b, c; // We use longs because we don't have unsigned ints |
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85 | a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK; |
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86 | int offset = 0; |
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87 | for (; length > 12; offset += 12, length -= 12) { |
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88 | a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; |
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89 | a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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90 | a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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91 | a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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92 | b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; |
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93 | b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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94 | b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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95 | b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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96 | c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; |
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97 | c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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98 | c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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99 | c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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100 | |
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101 | /* |
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102 | * mix -- mix 3 32-bit values reversibly. |
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103 | * This is reversible, so any information in (a,b,c) before mix() is |
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104 | * still in (a,b,c) after mix(). |
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105 | * |
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106 | * If four pairs of (a,b,c) inputs are run through mix(), or through |
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107 | * mix() in reverse, there are at least 32 bits of the output that |
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108 | * are sometimes the same for one pair and different for another pair. |
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109 | * |
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110 | * This was tested for: |
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111 | * - pairs that differed by one bit, by two bits, in any combination |
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112 | * of top bits of (a,b,c), or in any combination of bottom bits of |
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113 | * (a,b,c). |
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114 | * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed |
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115 | * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as |
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116 | * is commonly produced by subtraction) look like a single 1-bit |
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117 | * difference. |
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118 | * - the base values were pseudorandom, all zero but one bit set, or |
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119 | * all zero plus a counter that starts at zero. |
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120 | * |
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121 | * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that |
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122 | * satisfy this are |
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123 | * 4 6 8 16 19 4 |
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124 | * 9 15 3 18 27 15 |
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125 | * 14 9 3 7 17 3 |
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126 | * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for |
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127 | * "differ" defined as + with a one-bit base and a two-bit delta. I |
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128 | * used http://burtleburtle.net/bob/hash/avalanche.html to choose |
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129 | * the operations, constants, and arrangements of the variables. |
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130 | * |
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131 | * This does not achieve avalanche. There are input bits of (a,b,c) |
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132 | * that fail to affect some output bits of (a,b,c), especially of a. |
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133 | * The most thoroughly mixed value is c, but it doesn't really even |
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134 | * achieve avalanche in c. |
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135 | * |
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136 | * This allows some parallelism. Read-after-writes are good at doubling |
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137 | * the number of bits affected, so the goal of mixing pulls in the |
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138 | * opposite direction as the goal of parallelism. I did what I could. |
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139 | * Rotates seem to cost as much as shifts on every machine I could lay |
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140 | * my hands on, and rotates are much kinder to the top and bottom bits, |
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141 | * so I used rotates. |
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142 | * |
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143 | * #define mix(a,b,c) \ |
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144 | * { \ |
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145 | * a -= c; a ^= rot(c, 4); c += b; \ |
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146 | * b -= a; b ^= rot(a, 6); a += c; \ |
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147 | * c -= b; c ^= rot(b, 8); b += a; \ |
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148 | * a -= c; a ^= rot(c,16); c += b; \ |
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149 | * b -= a; b ^= rot(a,19); a += c; \ |
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150 | * c -= b; c ^= rot(b, 4); b += a; \ |
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151 | * } |
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152 | * |
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153 | * mix(a,b,c); |
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154 | */ |
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155 | a = (a - c) & INT_MASK; a ^= rot(c, 4); c = (c + b) & INT_MASK; |
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156 | b = (b - a) & INT_MASK; b ^= rot(a, 6); a = (a + c) & INT_MASK; |
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157 | c = (c - b) & INT_MASK; c ^= rot(b, 8); b = (b + a) & INT_MASK; |
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158 | a = (a - c) & INT_MASK; a ^= rot(c,16); c = (c + b) & INT_MASK; |
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159 | b = (b - a) & INT_MASK; b ^= rot(a,19); a = (a + c) & INT_MASK; |
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160 | c = (c - b) & INT_MASK; c ^= rot(b, 4); b = (b + a) & INT_MASK; |
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161 | } |
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162 | |
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163 | //-------------------------------- last block: affect all 32 bits of (c) |
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164 | switch (length) { // all the case statements fall through |
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165 | case 12: |
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166 | c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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167 | case 11: |
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168 | c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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169 | case 10: |
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170 | c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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171 | case 9: |
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172 | c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK; |
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173 | case 8: |
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174 | b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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175 | case 7: |
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176 | b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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177 | case 6: |
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178 | b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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179 | case 5: |
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180 | b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK; |
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181 | case 4: |
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182 | a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK; |
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183 | case 3: |
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184 | a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK; |
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185 | case 2: |
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186 | a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK; |
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187 | case 1: |
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188 | a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK; |
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189 | break; |
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190 | case 0: |
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191 | return (int)(c & INT_MASK); |
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192 | } |
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193 | /* |
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194 | * final -- final mixing of 3 32-bit values (a,b,c) into c |
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195 | * |
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196 | * Pairs of (a,b,c) values differing in only a few bits will usually |
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197 | * produce values of c that look totally different. This was tested for |
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198 | * - pairs that differed by one bit, by two bits, in any combination |
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199 | * of top bits of (a,b,c), or in any combination of bottom bits of |
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200 | * (a,b,c). |
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201 | * |
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202 | * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed |
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203 | * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as |
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204 | * is commonly produced by subtraction) look like a single 1-bit |
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205 | * difference. |
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206 | * |
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207 | * - the base values were pseudorandom, all zero but one bit set, or |
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208 | * all zero plus a counter that starts at zero. |
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209 | * |
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210 | * These constants passed: |
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211 | * 14 11 25 16 4 14 24 |
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212 | * 12 14 25 16 4 14 24 |
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213 | * and these came close: |
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214 | * 4 8 15 26 3 22 24 |
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215 | * 10 8 15 26 3 22 24 |
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216 | * 11 8 15 26 3 22 24 |
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217 | * |
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218 | * #define final(a,b,c) \ |
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219 | * { |
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220 | * c ^= b; c -= rot(b,14); \ |
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221 | * a ^= c; a -= rot(c,11); \ |
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222 | * b ^= a; b -= rot(a,25); \ |
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223 | * c ^= b; c -= rot(b,16); \ |
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224 | * a ^= c; a -= rot(c,4); \ |
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225 | * b ^= a; b -= rot(a,14); \ |
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226 | * c ^= b; c -= rot(b,24); \ |
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227 | * } |
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228 | * |
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229 | */ |
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230 | c ^= b; c = (c - rot(b,14)) & INT_MASK; |
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231 | a ^= c; a = (a - rot(c,11)) & INT_MASK; |
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232 | b ^= a; b = (b - rot(a,25)) & INT_MASK; |
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233 | c ^= b; c = (c - rot(b,16)) & INT_MASK; |
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234 | a ^= c; a = (a - rot(c,4)) & INT_MASK; |
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235 | b ^= a; b = (b - rot(a,14)) & INT_MASK; |
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236 | c ^= b; c = (c - rot(b,24)) & INT_MASK; |
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237 | |
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238 | return (int)(c & INT_MASK); |
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239 | } |
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240 | |
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241 | /** |
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242 | * Compute the hash of the specified file |
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243 | * @param args name of file to compute hash of. |
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244 | * @throws IOException |
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245 | */ |
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246 | public static void main(String[] args) throws IOException { |
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247 | if (args.length != 1) { |
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248 | System.err.println("Usage: JenkinsHash filename"); |
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249 | System.exit(-1); |
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250 | } |
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251 | FileInputStream in = new FileInputStream(args[0]); |
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252 | byte[] bytes = new byte[512]; |
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253 | int value = 0; |
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254 | JenkinsHash hash = new JenkinsHash(); |
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255 | for (int length = in.read(bytes); length > 0 ; length = in.read(bytes)) { |
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256 | value = hash.hash(bytes, length, value); |
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257 | } |
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258 | System.out.println(Math.abs(value)); |
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259 | } |
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260 | } |
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