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Annotation of embedaddon/quagga/lib/jhash.c, revision 1.1.1.1

1.1       misho       1: /* jhash.h: Jenkins hash support.
                      2:  *
                      3:  * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
                      4:  *
                      5:  * http://burtleburtle.net/bob/hash/
                      6:  *
                      7:  * These are the credits from Bob's sources:
                      8:  *
                      9:  * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
                     10:  * hash(), hash2(), hash3, and mix() are externally useful functions.
                     11:  * Routines to test the hash are included if SELF_TEST is defined.
                     12:  * You can use this free for any purpose.  It has no warranty.
                     13:  *
                     14:  * Copyright (C) 2003 David S. Miller (davem@redhat.com)
                     15:  *
                     16:  * I've modified Bob's hash to be useful in the Linux kernel, and
                     17:  * any bugs present are surely my fault.  -DaveM
                     18:  */
                     19: 
                     20: #include "zebra.h"
                     21: #include "jhash.h"
                     22: 
                     23: /* The golden ration: an arbitrary value */
                     24: #define JHASH_GOLDEN_RATIO  0x9e3779b9
                     25: 
                     26: /* NOTE: Arguments are modified. */
                     27: #define __jhash_mix(a, b, c) \
                     28: { \
                     29:   a -= b; a -= c; a ^= (c>>13); \
                     30:   b -= c; b -= a; b ^= (a<<8); \
                     31:   c -= a; c -= b; c ^= (b>>13); \
                     32:   a -= b; a -= c; a ^= (c>>12);  \
                     33:   b -= c; b -= a; b ^= (a<<16); \
                     34:   c -= a; c -= b; c ^= (b>>5); \
                     35:   a -= b; a -= c; a ^= (c>>3);  \
                     36:   b -= c; b -= a; b ^= (a<<10); \
                     37:   c -= a; c -= b; c ^= (b>>15); \
                     38: }
                     39: 
                     40: /* The most generic version, hashes an arbitrary sequence
                     41:  * of bytes.  No alignment or length assumptions are made about
                     42:  * the input key.
                     43:  */
                     44: u_int32_t
                     45: jhash (void *key, u_int32_t length, u_int32_t initval)
                     46: {
                     47:   u_int32_t a, b, c, len;
                     48:   u_int8_t *k = key;
                     49: 
                     50:   len = length;
                     51:   a = b = JHASH_GOLDEN_RATIO;
                     52:   c = initval;
                     53: 
                     54:   while (len >= 12)
                     55:     {
                     56:       a +=
                     57:         (k[0] + ((u_int32_t) k[1] << 8) + ((u_int32_t) k[2] << 16) +
                     58:          ((u_int32_t) k[3] << 24));
                     59:       b +=
                     60:         (k[4] + ((u_int32_t) k[5] << 8) + ((u_int32_t) k[6] << 16) +
                     61:          ((u_int32_t) k[7] << 24));
                     62:       c +=
                     63:         (k[8] + ((u_int32_t) k[9] << 8) + ((u_int32_t) k[10] << 16) +
                     64:          ((u_int32_t) k[11] << 24));
                     65: 
                     66:       __jhash_mix (a, b, c);
                     67: 
                     68:       k += 12;
                     69:       len -= 12;
                     70:     }
                     71: 
                     72:   c += length;
                     73:   switch (len)
                     74:     {
                     75:     case 11:
                     76:       c += ((u_int32_t) k[10] << 24);
                     77:     case 10:
                     78:       c += ((u_int32_t) k[9] << 16);
                     79:     case 9:
                     80:       c += ((u_int32_t) k[8] << 8);
                     81:     case 8:
                     82:       b += ((u_int32_t) k[7] << 24);
                     83:     case 7:
                     84:       b += ((u_int32_t) k[6] << 16);
                     85:     case 6:
                     86:       b += ((u_int32_t) k[5] << 8);
                     87:     case 5:
                     88:       b += k[4];
                     89:     case 4:
                     90:       a += ((u_int32_t) k[3] << 24);
                     91:     case 3:
                     92:       a += ((u_int32_t) k[2] << 16);
                     93:     case 2:
                     94:       a += ((u_int32_t) k[1] << 8);
                     95:     case 1:
                     96:       a += k[0];
                     97:     };
                     98: 
                     99:   __jhash_mix (a, b, c);
                    100: 
                    101:   return c;
                    102: }
                    103: 
                    104: /* A special optimized version that handles 1 or more of u_int32_ts.
                    105:  * The length parameter here is the number of u_int32_ts in the key.
                    106:  */
                    107: u_int32_t
                    108: jhash2 (u_int32_t * k, u_int32_t length, u_int32_t initval)
                    109: {
                    110:   u_int32_t a, b, c, len;
                    111: 
                    112:   a = b = JHASH_GOLDEN_RATIO;
                    113:   c = initval;
                    114:   len = length;
                    115: 
                    116:   while (len >= 3)
                    117:     {
                    118:       a += k[0];
                    119:       b += k[1];
                    120:       c += k[2];
                    121:       __jhash_mix (a, b, c);
                    122:       k += 3;
                    123:       len -= 3;
                    124:     }
                    125: 
                    126:   c += length * 4;
                    127: 
                    128:   switch (len)
                    129:     {
                    130:     case 2:
                    131:       b += k[1];
                    132:     case 1:
                    133:       a += k[0];
                    134:     };
                    135: 
                    136:   __jhash_mix (a, b, c);
                    137: 
                    138:   return c;
                    139: }
                    140: 
                    141: 
                    142: /* A special ultra-optimized versions that knows they are hashing exactly
                    143:  * 3, 2 or 1 word(s).
                    144:  *
                    145:  * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
                    146:  *       done at the end is not done here.
                    147:  */
                    148: u_int32_t
                    149: jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval)
                    150: {
                    151:   a += JHASH_GOLDEN_RATIO;
                    152:   b += JHASH_GOLDEN_RATIO;
                    153:   c += initval;
                    154: 
                    155:   __jhash_mix (a, b, c);
                    156: 
                    157:   return c;
                    158: }
                    159: 
                    160: u_int32_t
                    161: jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval)
                    162: {
                    163:   return jhash_3words (a, b, 0, initval);
                    164: }
                    165: 
                    166: u_int32_t
                    167: jhash_1word (u_int32_t a, u_int32_t initval)
                    168: {
                    169:   return jhash_3words (a, 0, 0, initval);
                    170: }