jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 1 | /* |
| 2 | -------------------------------------------------------------------- |
| 3 | lookupa.c, by Bob Jenkins, December 1996. Same as lookup2.c |
| 4 | Use this code however you wish. Public Domain. No warranty. |
| 5 | Source is http://burtleburtle.net/bob/c/lookupa.c |
| 6 | -------------------------------------------------------------------- |
| 7 | */ |
| 8 | #ifndef STANDARD |
| 9 | /* |
| 10 | #include "standard.h" |
| 11 | */ |
| 12 | #endif |
| 13 | #ifndef LOOKUPA |
| 14 | #include "lookupa.h" |
| 15 | #endif |
| 16 | |
| 17 | /* |
| 18 | -------------------------------------------------------------------- |
| 19 | mix -- mix 3 32-bit values reversibly. |
| 20 | For every delta with one or two bit set, and the deltas of all three |
| 21 | high bits or all three low bits, whether the original value of a,b,c |
| 22 | is almost all zero or is uniformly distributed, |
| 23 | * If mix() is run forward or backward, at least 32 bits in a,b,c |
| 24 | have at least 1/4 probability of changing. |
| 25 | * If mix() is run forward, every bit of c will change between 1/3 and |
| 26 | 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.) |
| 27 | mix() was built out of 36 single-cycle latency instructions in a |
| 28 | structure that could supported 2x parallelism, like so: |
| 29 | a -= b; |
| 30 | a -= c; x = (c>>13); |
| 31 | b -= c; a ^= x; |
| 32 | b -= a; x = (a<<8); |
| 33 | c -= a; b ^= x; |
| 34 | c -= b; x = (b>>13); |
| 35 | ... |
| 36 | Unfortunately, superscalar Pentiums and Sparcs can't take advantage |
| 37 | of that parallelism. They've also turned some of those single-cycle |
| 38 | latency instructions into multi-cycle latency instructions. Still, |
| 39 | this is the fastest good hash I could find. There were about 2^^68 |
| 40 | to choose from. I only looked at a billion or so. |
| 41 | -------------------------------------------------------------------- |
| 42 | */ |
| 43 | #define mix(a,b,c) \ |
| 44 | { \ |
| 45 | a -= b; a -= c; a ^= (c>>13); \ |
| 46 | b -= c; b -= a; b ^= (a<<8); \ |
| 47 | c -= a; c -= b; c ^= (b>>13); \ |
| 48 | a -= b; a -= c; a ^= (c>>12); \ |
| 49 | b -= c; b -= a; b ^= (a<<16); \ |
| 50 | c -= a; c -= b; c ^= (b>>5); \ |
| 51 | a -= b; a -= c; a ^= (c>>3); \ |
| 52 | b -= c; b -= a; b ^= (a<<10); \ |
| 53 | c -= a; c -= b; c ^= (b>>15); \ |
| 54 | } |
| 55 | |
| 56 | /* |
| 57 | -------------------------------------------------------------------- |
| 58 | lookup() -- hash a variable-length key into a 32-bit value |
| 59 | k : the key (the unaligned variable-length array of bytes) |
| 60 | len : the length of the key, counting by bytes |
| 61 | level : can be any 4-byte value |
| 62 | Returns a 32-bit value. Every bit of the key affects every bit of |
| 63 | the return value. Every 1-bit and 2-bit delta achieves avalanche. |
| 64 | About 6len+35 instructions. |
| 65 | |
| 66 | The best hash table sizes are powers of 2. There is no need to do |
| 67 | mod a prime (mod is sooo slow!). If you need less than 32 bits, |
| 68 | use a bitmask. For example, if you need only 10 bits, do |
| 69 | h = (h & hashmask(10)); |
| 70 | In which case, the hash table should have hashsize(10) elements. |
| 71 | |
| 72 | If you are hashing n strings (ub1 **)k, do it like this: |
| 73 | for (i=0, h=0; i<n; ++i) h = lookup( k[i], len[i], h); |
| 74 | |
| 75 | By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this |
| 76 | code any way you wish, private, educational, or commercial. |
| 77 | |
| 78 | See http://burtleburtle.net/bob/hash/evahash.html |
| 79 | Use for hash table lookup, or anything where one collision in 2^32 is |
| 80 | acceptable. Do NOT use for cryptographic purposes. |
| 81 | -------------------------------------------------------------------- |
| 82 | */ |
| 83 | |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 84 | ub4 lookup(k, length, level) |
| 85 | register ub1 *k; /* the key */ |
| 86 | register ub4 length; /* the length of the key */ |
| 87 | register ub4 level; /* the previous hash, or an arbitrary value */ |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 88 | { |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 89 | register ub4 a, b, c, len; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 90 | |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 91 | /* Set up the internal state */ |
| 92 | len = length; |
| 93 | a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */ |
| 94 | c = level; /* the previous hash value */ |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 95 | |
| 96 | /*---------------------------------------- handle most of the key */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 97 | while (len >= 12) { |
| 98 | a += (k[0] + ((ub4) k[1] << 8) + ((ub4) k[2] << 16) + |
| 99 | ((ub4) k[3] << 24)); |
| 100 | b += (k[4] + ((ub4) k[5] << 8) + ((ub4) k[6] << 16) + |
| 101 | ((ub4) k[7] << 24)); |
| 102 | c += (k[8] + ((ub4) k[9] << 8) + ((ub4) k[10] << 16) + |
| 103 | ((ub4) k[11] << 24)); |
| 104 | mix(a, b, c); |
| 105 | k += 12; |
| 106 | len -= 12; |
| 107 | } |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 108 | |
| 109 | /*------------------------------------- handle the last 11 bytes */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 110 | c += length; |
| 111 | switch (len) { /* all the case statements fall through */ |
| 112 | case 11: |
| 113 | c += ((ub4) k[10] << 24); |
| 114 | case 10: |
| 115 | c += ((ub4) k[9] << 16); |
| 116 | case 9: |
| 117 | c += ((ub4) k[8] << 8); |
| 118 | /* the first byte of c is reserved for the length */ |
| 119 | case 8: |
| 120 | b += ((ub4) k[7] << 24); |
| 121 | case 7: |
| 122 | b += ((ub4) k[6] << 16); |
| 123 | case 6: |
| 124 | b += ((ub4) k[5] << 8); |
| 125 | case 5: |
| 126 | b += k[4]; |
| 127 | case 4: |
| 128 | a += ((ub4) k[3] << 24); |
| 129 | case 3: |
| 130 | a += ((ub4) k[2] << 16); |
| 131 | case 2: |
| 132 | a += ((ub4) k[1] << 8); |
| 133 | case 1: |
| 134 | a += k[0]; |
| 135 | /* case 0: nothing left to add */ |
| 136 | } |
| 137 | mix(a, b, c); |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 138 | /*-------------------------------------------- report the result */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 139 | return c; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 140 | } |
| 141 | |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 142 | /* |
| 143 | -------------------------------------------------------------------- |
| 144 | mixc -- mixc 8 4-bit values as quickly and thoroughly as possible. |
| 145 | Repeating mix() three times achieves avalanche. |
| 146 | Repeating mix() four times eliminates all funnels and all |
| 147 | characteristics stronger than 2^{-11}. |
| 148 | -------------------------------------------------------------------- |
| 149 | */ |
| 150 | #define mixc(a,b,c,d,e,f,g,h) \ |
| 151 | { \ |
| 152 | a^=b<<11; d+=a; b+=c; \ |
| 153 | b^=c>>2; e+=b; c+=d; \ |
| 154 | c^=d<<8; f+=c; d+=e; \ |
| 155 | d^=e>>16; g+=d; e+=f; \ |
| 156 | e^=f<<10; h+=e; f+=g; \ |
| 157 | f^=g>>4; a+=f; g+=h; \ |
| 158 | g^=h<<8; b+=g; h+=a; \ |
| 159 | h^=a>>9; c+=h; a+=b; \ |
| 160 | } |
| 161 | |
| 162 | /* |
| 163 | -------------------------------------------------------------------- |
| 164 | checksum() -- hash a variable-length key into a 256-bit value |
| 165 | k : the key (the unaligned variable-length array of bytes) |
| 166 | len : the length of the key, counting by bytes |
| 167 | state : an array of CHECKSTATE 4-byte values (256 bits) |
| 168 | The state is the checksum. Every bit of the key affects every bit of |
| 169 | the state. There are no funnels. About 112+6.875len instructions. |
| 170 | |
| 171 | If you are hashing n strings (ub1 **)k, do it like this: |
| 172 | for (i=0; i<8; ++i) state[i] = 0x9e3779b9; |
| 173 | for (i=0, h=0; i<n; ++i) checksum( k[i], len[i], state); |
| 174 | |
| 175 | (c) Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this |
| 176 | code any way you wish, private, educational, or commercial, as long |
| 177 | as this whole comment accompanies it. |
| 178 | |
| 179 | See http://burtleburtle.net/bob/hash/evahash.html |
| 180 | Use to detect changes between revisions of documents, assuming nobody |
| 181 | is trying to cause collisions. Do NOT use for cryptography. |
| 182 | -------------------------------------------------------------------- |
| 183 | */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 184 | void checksum(k, len, state) |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 185 | register ub1 *k; |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 186 | register ub4 len; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 187 | register ub4 *state; |
| 188 | { |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 189 | register ub4 a, b, c, d, e, f, g, h, length; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 190 | |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 191 | /* Use the length and level; add in the golden ratio. */ |
| 192 | length = len; |
| 193 | a = state[0]; |
| 194 | b = state[1]; |
| 195 | c = state[2]; |
| 196 | d = state[3]; |
| 197 | e = state[4]; |
| 198 | f = state[5]; |
| 199 | g = state[6]; |
| 200 | h = state[7]; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 201 | |
| 202 | /*---------------------------------------- handle most of the key */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 203 | while (len >= 32) { |
| 204 | a += (k[0] + (k[1] << 8) + (k[2] << 16) + (k[3] << 24)); |
| 205 | b += (k[4] + (k[5] << 8) + (k[6] << 16) + (k[7] << 24)); |
| 206 | c += (k[8] + (k[9] << 8) + (k[10] << 16) + (k[11] << 24)); |
| 207 | d += (k[12] + (k[13] << 8) + (k[14] << 16) + (k[15] << 24)); |
| 208 | e += (k[16] + (k[17] << 8) + (k[18] << 16) + (k[19] << 24)); |
| 209 | f += (k[20] + (k[21] << 8) + (k[22] << 16) + (k[23] << 24)); |
| 210 | g += (k[24] + (k[25] << 8) + (k[26] << 16) + (k[27] << 24)); |
| 211 | h += (k[28] + (k[29] << 8) + (k[30] << 16) + (k[31] << 24)); |
| 212 | mixc(a, b, c, d, e, f, g, h); |
| 213 | mixc(a, b, c, d, e, f, g, h); |
| 214 | mixc(a, b, c, d, e, f, g, h); |
| 215 | mixc(a, b, c, d, e, f, g, h); |
| 216 | k += 32; |
| 217 | len -= 32; |
| 218 | } |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 219 | |
| 220 | /*------------------------------------- handle the last 31 bytes */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 221 | h += length; |
| 222 | switch (len) { |
| 223 | case 31: |
| 224 | h += (k[30] << 24); |
| 225 | case 30: |
| 226 | h += (k[29] << 16); |
| 227 | case 29: |
| 228 | h += (k[28] << 8); |
| 229 | case 28: |
| 230 | g += (k[27] << 24); |
| 231 | case 27: |
| 232 | g += (k[26] << 16); |
| 233 | case 26: |
| 234 | g += (k[25] << 8); |
| 235 | case 25: |
| 236 | g += k[24]; |
| 237 | case 24: |
| 238 | f += (k[23] << 24); |
| 239 | case 23: |
| 240 | f += (k[22] << 16); |
| 241 | case 22: |
| 242 | f += (k[21] << 8); |
| 243 | case 21: |
| 244 | f += k[20]; |
| 245 | case 20: |
| 246 | e += (k[19] << 24); |
| 247 | case 19: |
| 248 | e += (k[18] << 16); |
| 249 | case 18: |
| 250 | e += (k[17] << 8); |
| 251 | case 17: |
| 252 | e += k[16]; |
| 253 | case 16: |
| 254 | d += (k[15] << 24); |
| 255 | case 15: |
| 256 | d += (k[14] << 16); |
| 257 | case 14: |
| 258 | d += (k[13] << 8); |
| 259 | case 13: |
| 260 | d += k[12]; |
| 261 | case 12: |
| 262 | c += (k[11] << 24); |
| 263 | case 11: |
| 264 | c += (k[10] << 16); |
| 265 | case 10: |
| 266 | c += (k[9] << 8); |
| 267 | case 9: |
| 268 | c += k[8]; |
| 269 | case 8: |
| 270 | b += (k[7] << 24); |
| 271 | case 7: |
| 272 | b += (k[6] << 16); |
| 273 | case 6: |
| 274 | b += (k[5] << 8); |
| 275 | case 5: |
| 276 | b += k[4]; |
| 277 | case 4: |
| 278 | a += (k[3] << 24); |
| 279 | case 3: |
| 280 | a += (k[2] << 16); |
| 281 | case 2: |
| 282 | a += (k[1] << 8); |
| 283 | case 1: |
| 284 | a += k[0]; |
| 285 | } |
| 286 | mixc(a, b, c, d, e, f, g, h); |
| 287 | mixc(a, b, c, d, e, f, g, h); |
| 288 | mixc(a, b, c, d, e, f, g, h); |
| 289 | mixc(a, b, c, d, e, f, g, h); |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 290 | |
| 291 | /*-------------------------------------------- report the result */ |
Harald Welte | bed35df | 2011-11-02 13:06:18 +0100 | [diff] [blame] | 292 | state[0] = a; |
| 293 | state[1] = b; |
| 294 | state[2] = c; |
| 295 | state[3] = d; |
| 296 | state[4] = e; |
| 297 | state[5] = f; |
| 298 | state[6] = g; |
| 299 | state[7] = h; |
jjako | 52c2414 | 2002-12-16 13:33:51 +0000 | [diff] [blame] | 300 | } |