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1 /* |
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2 ------------------------------------------------------------------------------- |
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3 lookup3.c, by Bob Jenkins, May 2006, Public Domain. |
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4 |
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5 These are functions for producing 32-bit hashes for hash table lookup. |
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6 hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() |
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7 are externally useful functions. Routines to test the hash are included |
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8 if SELF_TEST is defined. You can use this free for any purpose. It's in |
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9 the public domain. It has no warranty. |
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10 |
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11 You probably want to use hashlittle(). hashlittle() and hashbig() |
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12 hash byte arrays. hashlittle() is is faster than hashbig() on |
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13 little-endian machines. Intel and AMD are little-endian machines. |
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14 On second thought, you probably want hashlittle2(), which is identical to |
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15 hashlittle() except it returns two 32-bit hashes for the price of one. |
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16 You could implement hashbig2() if you wanted but I haven't bothered here. |
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17 |
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18 If you want to find a hash of, say, exactly 7 integers, do |
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19 a = i1; b = i2; c = i3; |
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20 mix(a,b,c); |
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21 a += i4; b += i5; c += i6; |
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22 mix(a,b,c); |
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23 a += i7; |
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24 final(a,b,c); |
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25 then use c as the hash value. If you have a variable length array of |
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26 4-byte integers to hash, use hashword(). If you have a byte array (like |
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27 a character string), use hashlittle(). If you have several byte arrays, or |
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28 a mix of things, see the comments above hashlittle(). |
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29 |
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30 Why is this so big? I read 12 bytes at a time into 3 4-byte integers, |
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31 then mix those integers. This is fast (you can do a lot more thorough |
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32 mixing with 12*3 instructions on 3 integers than you can with 3 instructions |
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33 on 1 byte), but shoehorning those bytes into integers efficiently is messy. |
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34 ------------------------------------------------------------------------------- |
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35 */ |
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36 |
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37 #include <stdlib.h> |
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38 |
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39 #ifdef HAVE_CONFIG_H |
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40 #include <jansson_private_config.h> |
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41 #endif |
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42 |
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43 #ifdef HAVE_STDINT_H |
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44 #include <stdint.h> /* defines uint32_t etc */ |
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45 #endif |
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46 |
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47 #ifdef HAVE_SYS_PARAM_H |
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48 #include <sys/param.h> /* attempt to define endianness */ |
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49 #endif |
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50 |
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51 #ifdef HAVE_ENDIAN_H |
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52 # include <endian.h> /* attempt to define endianness */ |
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53 #endif |
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54 |
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55 /* |
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56 * My best guess at if you are big-endian or little-endian. This may |
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57 * need adjustment. |
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58 */ |
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59 #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \ |
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60 __BYTE_ORDER == __LITTLE_ENDIAN) || \ |
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61 (defined(i386) || defined(__i386__) || defined(__i486__) || \ |
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62 defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL)) |
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63 # define HASH_LITTLE_ENDIAN 1 |
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64 # define HASH_BIG_ENDIAN 0 |
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65 #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \ |
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66 __BYTE_ORDER == __BIG_ENDIAN) || \ |
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67 (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel)) |
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68 # define HASH_LITTLE_ENDIAN 0 |
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69 # define HASH_BIG_ENDIAN 1 |
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70 #else |
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71 # define HASH_LITTLE_ENDIAN 0 |
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72 # define HASH_BIG_ENDIAN 0 |
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73 #endif |
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74 |
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75 #define hashsize(n) ((uint32_t)1<<(n)) |
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76 #define hashmask(n) (hashsize(n)-1) |
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77 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k)))) |
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78 |
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79 /* |
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80 ------------------------------------------------------------------------------- |
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81 mix -- mix 3 32-bit values reversibly. |
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82 |
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83 This is reversible, so any information in (a,b,c) before mix() is |
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84 still in (a,b,c) after mix(). |
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85 |
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86 If four pairs of (a,b,c) inputs are run through mix(), or through |
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87 mix() in reverse, there are at least 32 bits of the output that |
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88 are sometimes the same for one pair and different for another pair. |
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89 This was tested for: |
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90 * pairs that differed by one bit, by two bits, in any combination |
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91 of top bits of (a,b,c), or in any combination of bottom bits of |
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92 (a,b,c). |
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93 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed |
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94 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as |
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95 is commonly produced by subtraction) look like a single 1-bit |
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96 difference. |
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97 * the base values were pseudorandom, all zero but one bit set, or |
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98 all zero plus a counter that starts at zero. |
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99 |
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100 Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that |
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101 satisfy this are |
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102 4 6 8 16 19 4 |
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103 9 15 3 18 27 15 |
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104 14 9 3 7 17 3 |
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105 Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing |
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106 for "differ" defined as + with a one-bit base and a two-bit delta. I |
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107 used http://burtleburtle.net/bob/hash/avalanche.html to choose |
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108 the operations, constants, and arrangements of the variables. |
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109 |
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110 This does not achieve avalanche. There are input bits of (a,b,c) |
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111 that fail to affect some output bits of (a,b,c), especially of a. The |
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112 most thoroughly mixed value is c, but it doesn't really even achieve |
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113 avalanche in c. |
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114 |
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115 This allows some parallelism. Read-after-writes are good at doubling |
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116 the number of bits affected, so the goal of mixing pulls in the opposite |
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117 direction as the goal of parallelism. I did what I could. Rotates |
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118 seem to cost as much as shifts on every machine I could lay my hands |
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119 on, and rotates are much kinder to the top and bottom bits, so I used |
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120 rotates. |
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121 ------------------------------------------------------------------------------- |
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122 */ |
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123 #define mix(a,b,c) \ |
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124 { \ |
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125 a -= c; a ^= rot(c, 4); c += b; \ |
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126 b -= a; b ^= rot(a, 6); a += c; \ |
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127 c -= b; c ^= rot(b, 8); b += a; \ |
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128 a -= c; a ^= rot(c,16); c += b; \ |
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129 b -= a; b ^= rot(a,19); a += c; \ |
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130 c -= b; c ^= rot(b, 4); b += a; \ |
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131 } |
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132 |
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133 /* |
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134 ------------------------------------------------------------------------------- |
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135 final -- final mixing of 3 32-bit values (a,b,c) into c |
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136 |
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137 Pairs of (a,b,c) values differing in only a few bits will usually |
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138 produce values of c that look totally different. This was tested for |
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139 * pairs that differed by one bit, by two bits, in any combination |
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140 of top bits of (a,b,c), or in any combination of bottom bits of |
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141 (a,b,c). |
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142 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed |
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143 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as |
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144 is commonly produced by subtraction) look like a single 1-bit |
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145 difference. |
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146 * the base values were pseudorandom, all zero but one bit set, or |
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147 all zero plus a counter that starts at zero. |
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148 |
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149 These constants passed: |
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150 14 11 25 16 4 14 24 |
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151 12 14 25 16 4 14 24 |
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152 and these came close: |
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153 4 8 15 26 3 22 24 |
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154 10 8 15 26 3 22 24 |
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155 11 8 15 26 3 22 24 |
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156 ------------------------------------------------------------------------------- |
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157 */ |
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158 #define final(a,b,c) \ |
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159 { \ |
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160 c ^= b; c -= rot(b,14); \ |
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161 a ^= c; a -= rot(c,11); \ |
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162 b ^= a; b -= rot(a,25); \ |
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163 c ^= b; c -= rot(b,16); \ |
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164 a ^= c; a -= rot(c,4); \ |
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165 b ^= a; b -= rot(a,14); \ |
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166 c ^= b; c -= rot(b,24); \ |
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167 } |
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168 |
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169 /* |
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170 ------------------------------------------------------------------------------- |
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171 hashlittle() -- hash a variable-length key into a 32-bit value |
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172 k : the key (the unaligned variable-length array of bytes) |
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173 length : the length of the key, counting by bytes |
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174 initval : can be any 4-byte value |
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175 Returns a 32-bit value. Every bit of the key affects every bit of |
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176 the return value. Two keys differing by one or two bits will have |
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177 totally different hash values. |
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178 |
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179 The best hash table sizes are powers of 2. There is no need to do |
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180 mod a prime (mod is sooo slow!). If you need less than 32 bits, |
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181 use a bitmask. For example, if you need only 10 bits, do |
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182 h = (h & hashmask(10)); |
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183 In which case, the hash table should have hashsize(10) elements. |
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184 |
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185 If you are hashing n strings (uint8_t **)k, do it like this: |
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186 for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h); |
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187 |
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188 By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this |
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189 code any way you wish, private, educational, or commercial. It's free. |
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190 |
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191 Use for hash table lookup, or anything where one collision in 2^^32 is |
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192 acceptable. Do NOT use for cryptographic purposes. |
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193 ------------------------------------------------------------------------------- |
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194 */ |
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195 |
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196 static uint32_t hashlittle(const void *key, size_t length, uint32_t initval) |
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197 { |
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198 uint32_t a,b,c; /* internal state */ |
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199 union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */ |
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200 |
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201 /* Set up the internal state */ |
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202 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval; |
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203 |
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204 u.ptr = key; |
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205 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) { |
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206 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */ |
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207 |
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208 /* Detect Valgrind or AddressSanitizer */ |
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209 #ifdef VALGRIND |
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210 # define NO_MASKING_TRICK 1 |
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211 #else |
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212 # if defined(__has_feature) /* Clang */ |
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213 # if __has_feature(address_sanitizer) /* is ASAN enabled? */ |
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214 # define NO_MASKING_TRICK 1 |
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215 # endif |
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216 # else |
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217 # if defined(__SANITIZE_ADDRESS__) /* GCC 4.8.x, is ASAN enabled? */ |
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218 # define NO_MASKING_TRICK 1 |
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219 # endif |
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220 # endif |
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221 #endif |
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222 |
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223 #ifdef NO_MASKING_TRICK |
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224 const uint8_t *k8; |
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225 #endif |
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226 |
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227 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */ |
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228 while (length > 12) |
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229 { |
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230 a += k[0]; |
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231 b += k[1]; |
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232 c += k[2]; |
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233 mix(a,b,c); |
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234 length -= 12; |
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235 k += 3; |
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236 } |
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237 |
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238 /*----------------------------- handle the last (probably partial) block */ |
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239 /* |
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240 * "k[2]&0xffffff" actually reads beyond the end of the string, but |
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241 * then masks off the part it's not allowed to read. Because the |
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242 * string is aligned, the masked-off tail is in the same word as the |
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243 * rest of the string. Every machine with memory protection I've seen |
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244 * does it on word boundaries, so is OK with this. But VALGRIND will |
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245 * still catch it and complain. The masking trick does make the hash |
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246 * noticably faster for short strings (like English words). |
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247 */ |
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248 #ifndef NO_MASKING_TRICK |
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249 |
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250 switch(length) |
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251 { |
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252 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; |
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253 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break; |
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254 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break; |
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255 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break; |
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256 case 8 : b+=k[1]; a+=k[0]; break; |
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257 case 7 : b+=k[1]&0xffffff; a+=k[0]; break; |
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258 case 6 : b+=k[1]&0xffff; a+=k[0]; break; |
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259 case 5 : b+=k[1]&0xff; a+=k[0]; break; |
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260 case 4 : a+=k[0]; break; |
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261 case 3 : a+=k[0]&0xffffff; break; |
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262 case 2 : a+=k[0]&0xffff; break; |
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263 case 1 : a+=k[0]&0xff; break; |
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264 case 0 : return c; /* zero length strings require no mixing */ |
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265 } |
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266 |
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267 #else /* make valgrind happy */ |
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268 |
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269 k8 = (const uint8_t *)k; |
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270 switch(length) |
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271 { |
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272 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; |
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273 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ |
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274 case 10: c+=((uint32_t)k8[9])<<8; /* fall through */ |
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275 case 9 : c+=k8[8]; /* fall through */ |
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276 case 8 : b+=k[1]; a+=k[0]; break; |
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277 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ |
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278 case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */ |
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279 case 5 : b+=k8[4]; /* fall through */ |
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280 case 4 : a+=k[0]; break; |
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281 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ |
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282 case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */ |
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283 case 1 : a+=k8[0]; break; |
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284 case 0 : return c; |
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285 } |
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286 |
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287 #endif /* !valgrind */ |
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288 |
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289 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) { |
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290 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */ |
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291 const uint8_t *k8; |
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292 |
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293 /*--------------- all but last block: aligned reads and different mixing */ |
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294 while (length > 12) |
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295 { |
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296 a += k[0] + (((uint32_t)k[1])<<16); |
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297 b += k[2] + (((uint32_t)k[3])<<16); |
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298 c += k[4] + (((uint32_t)k[5])<<16); |
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299 mix(a,b,c); |
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300 length -= 12; |
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301 k += 6; |
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302 } |
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303 |
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304 /*----------------------------- handle the last (probably partial) block */ |
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305 k8 = (const uint8_t *)k; |
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306 switch(length) |
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307 { |
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308 case 12: c+=k[4]+(((uint32_t)k[5])<<16); |
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309 b+=k[2]+(((uint32_t)k[3])<<16); |
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310 a+=k[0]+(((uint32_t)k[1])<<16); |
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311 break; |
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312 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ |
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313 case 10: c+=k[4]; |
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314 b+=k[2]+(((uint32_t)k[3])<<16); |
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315 a+=k[0]+(((uint32_t)k[1])<<16); |
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316 break; |
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317 case 9 : c+=k8[8]; /* fall through */ |
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318 case 8 : b+=k[2]+(((uint32_t)k[3])<<16); |
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319 a+=k[0]+(((uint32_t)k[1])<<16); |
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320 break; |
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321 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ |
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322 case 6 : b+=k[2]; |
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323 a+=k[0]+(((uint32_t)k[1])<<16); |
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324 break; |
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325 case 5 : b+=k8[4]; /* fall through */ |
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326 case 4 : a+=k[0]+(((uint32_t)k[1])<<16); |
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327 break; |
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328 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ |
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329 case 2 : a+=k[0]; |
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330 break; |
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331 case 1 : a+=k8[0]; |
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332 break; |
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333 case 0 : return c; /* zero length requires no mixing */ |
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334 } |
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335 |
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336 } else { /* need to read the key one byte at a time */ |
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337 const uint8_t *k = (const uint8_t *)key; |
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338 |
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339 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */ |
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340 while (length > 12) |
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341 { |
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342 a += k[0]; |
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343 a += ((uint32_t)k[1])<<8; |
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344 a += ((uint32_t)k[2])<<16; |
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345 a += ((uint32_t)k[3])<<24; |
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346 b += k[4]; |
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347 b += ((uint32_t)k[5])<<8; |
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348 b += ((uint32_t)k[6])<<16; |
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349 b += ((uint32_t)k[7])<<24; |
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350 c += k[8]; |
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351 c += ((uint32_t)k[9])<<8; |
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352 c += ((uint32_t)k[10])<<16; |
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353 c += ((uint32_t)k[11])<<24; |
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354 mix(a,b,c); |
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355 length -= 12; |
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356 k += 12; |
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357 } |
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358 |
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359 /*-------------------------------- last block: affect all 32 bits of (c) */ |
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360 switch(length) /* all the case statements fall through */ |
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361 { |
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362 case 12: c+=((uint32_t)k[11])<<24; |
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363 case 11: c+=((uint32_t)k[10])<<16; |
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364 case 10: c+=((uint32_t)k[9])<<8; |
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365 case 9 : c+=k[8]; |
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366 case 8 : b+=((uint32_t)k[7])<<24; |
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367 case 7 : b+=((uint32_t)k[6])<<16; |
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368 case 6 : b+=((uint32_t)k[5])<<8; |
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369 case 5 : b+=k[4]; |
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370 case 4 : a+=((uint32_t)k[3])<<24; |
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371 case 3 : a+=((uint32_t)k[2])<<16; |
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372 case 2 : a+=((uint32_t)k[1])<<8; |
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373 case 1 : a+=k[0]; |
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374 break; |
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375 case 0 : return c; |
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376 } |
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377 } |
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378 |
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379 final(a,b,c); |
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380 return c; |
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381 } |
