| /* |
| * Hash lookup function. |
| * Copyright (C) 2003, 2004 Mondru AB. |
| * |
| * The contents of this file may be used under the terms of the GNU |
| * General Public License Version 2, provided that the above copyright |
| * notice and this permission notice is included in all copies or |
| * substantial portions of the software. |
| * |
| */ |
| |
| /** |
| * lookup() |
| * Generates a 32 bit hash. |
| * Based on public domain code by Bob Jenkins |
| * It should be one of the best hash functions around in terms of both |
| * statistical properties and speed. It is NOT recommended for cryptographic |
| * purposes. |
| **/ |
| unsigned long int lookup(k, length, level) |
| register unsigned char *k; /* the key */ |
| register unsigned long int length; /* the length of the key */ |
| register unsigned long int level; /* the previous hash, or an arbitrary value */ |
| { |
| |
| #define mix(a,b,c) \ |
| { \ |
| a -= b; a -= c; a ^= (c>>13); \ |
| b -= c; b -= a; b ^= (a<<8); \ |
| c -= a; c -= b; c ^= (b>>13); \ |
| a -= b; a -= c; a ^= (c>>12); \ |
| b -= c; b -= a; b ^= (a<<16); \ |
| c -= a; c -= b; c ^= (b>>5); \ |
| a -= b; a -= c; a ^= (c>>3); \ |
| b -= c; b -= a; b ^= (a<<10); \ |
| c -= a; c -= b; c ^= (b>>15); \ |
| } |
| |
| typedef unsigned long int ub4; /* unsigned 4-byte quantities */ |
| register unsigned long int a, b, c, len; |
| |
| /* Set up the internal state */ |
| len = length; |
| a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */ |
| c = level; /* the previous hash value */ |
| |
| /*---------------------------------------- handle most of the key */ |
| while (len >= 12) { |
| a += (k[0] + ((ub4) k[1] << 8) + ((ub4) k[2] << 16) + |
| ((ub4) k[3] << 24)); |
| b += (k[4] + ((ub4) k[5] << 8) + ((ub4) k[6] << 16) + |
| ((ub4) k[7] << 24)); |
| c += (k[8] + ((ub4) k[9] << 8) + ((ub4) k[10] << 16) + |
| ((ub4) k[11] << 24)); |
| mix(a, b, c); |
| k += 12; |
| len -= 12; |
| } |
| |
| /*------------------------------------- handle the last 11 bytes */ |
| c += length; |
| switch (len) { /* all the case statements fall through */ |
| case 11: |
| c += ((ub4) k[10] << 24); |
| case 10: |
| c += ((ub4) k[9] << 16); |
| case 9: |
| c += ((ub4) k[8] << 8); |
| /* the first byte of c is reserved for the length */ |
| case 8: |
| b += ((ub4) k[7] << 24); |
| case 7: |
| b += ((ub4) k[6] << 16); |
| case 6: |
| b += ((ub4) k[5] << 8); |
| case 5: |
| b += k[4]; |
| case 4: |
| a += ((ub4) k[3] << 24); |
| case 3: |
| a += ((ub4) k[2] << 16); |
| case 2: |
| a += ((ub4) k[1] << 8); |
| case 1: |
| a += k[0]; |
| /* case 0: nothing left to add */ |
| } |
| mix(a, b, c); |
| /*-------------------------------------------- report the result */ |
| return c; |
| } |