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Diffstat (limited to 'lib/jhash.c')
| -rw-r--r-- | lib/jhash.c | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/lib/jhash.c b/lib/jhash.c new file mode 100644 index 0000000..0d561ef --- /dev/null +++ b/lib/jhash.c @@ -0,0 +1,187 @@ +/* jhash.h: Jenkins hash support. + * + * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net) + * + * http://burtleburtle.net/bob/hash/ + * + * These are the credits from Bob's sources: + * + * lookup2.c, by Bob Jenkins, December 1996, Public Domain. + * hash(), hash2(), hash3, and mix() are externally useful functions. + * Routines to test the hash are included if SELF_TEST is defined. + * You can use this free for any purpose. It has no warranty. + * + * Copyright (C) 2003 David S. Miller (davem@redhat.com) + * + * I've modified Bob's hash to be useful in the Linux kernel, and + * any bugs present are surely my fault. -DaveM + */ + +#include "zebra.h" +#include "jhash.h" + +/* The golden ration: an arbitrary value */ +#define JHASH_GOLDEN_RATIO 0x9e3779b9 + +/* NOTE: Arguments are modified. */ +#define __jhash_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); \ + } + +/* The most generic version, hashes an arbitrary sequence + * of bytes. No alignment or length assumptions are made about + * the input key. + */ +uint32_t jhash(const void *key, uint32_t length, uint32_t initval) +{ + uint32_t a, b, c, len; + const uint8_t *k = key; + + len = length; + a = b = JHASH_GOLDEN_RATIO; + c = initval; + + while (len >= 12) { + a += (k[0] + ((uint32_t)k[1] << 8) + ((uint32_t)k[2] << 16) + + ((uint32_t)k[3] << 24)); + b += (k[4] + ((uint32_t)k[5] << 8) + ((uint32_t)k[6] << 16) + + ((uint32_t)k[7] << 24)); + c += (k[8] + ((uint32_t)k[9] << 8) + ((uint32_t)k[10] << 16) + + ((uint32_t)k[11] << 24)); + + __jhash_mix(a, b, c); + + k += 12; + len -= 12; + } + + c += length; + switch (len) { + case 11: + c += ((uint32_t)k[10] << 24); + /* fallthru */ + case 10: + c += ((uint32_t)k[9] << 16); + /* fallthru */ + case 9: + c += ((uint32_t)k[8] << 8); + /* fallthru */ + case 8: + b += ((uint32_t)k[7] << 24); + /* fallthru */ + case 7: + b += ((uint32_t)k[6] << 16); + /* fallthru */ + case 6: + b += ((uint32_t)k[5] << 8); + /* fallthru */ + case 5: + b += k[4]; + /* fallthru */ + case 4: + a += ((uint32_t)k[3] << 24); + /* fallthru */ + case 3: + a += ((uint32_t)k[2] << 16); + /* fallthru */ + case 2: + a += ((uint32_t)k[1] << 8); + /* fallthru */ + case 1: + a += k[0]; + } + + __jhash_mix(a, b, c); + + return c; +} + +/* A special optimized version that handles 1 or more of uint32_ts. + * The length parameter here is the number of uint32_ts in the key. + */ +uint32_t jhash2(const uint32_t *k, uint32_t length, uint32_t initval) +{ + uint32_t a, b, c, len; + + a = b = JHASH_GOLDEN_RATIO; + c = initval; + len = length; + + while (len >= 3) { + a += k[0]; + b += k[1]; + c += k[2]; + __jhash_mix(a, b, c); + k += 3; + len -= 3; + } + + c += length * 4; + + switch (len) { + case 2: + b += k[1]; + /* fallthru */ + case 1: + a += k[0]; + } + + __jhash_mix(a, b, c); + + return c; +} + + +/* A special ultra-optimized versions that knows they are hashing exactly + * 3, 2 or 1 word(s). + * + * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally + * done at the end is not done here. + */ +uint32_t jhash_3words(uint32_t a, uint32_t b, uint32_t c, uint32_t initval) +{ + a += JHASH_GOLDEN_RATIO; + b += JHASH_GOLDEN_RATIO; + c += initval; + + __jhash_mix(a, b, c); + + return c; +} + +uint32_t jhash_2words(uint32_t a, uint32_t b, uint32_t initval) +{ + return jhash_3words(a, b, 0, initval); +} + +uint32_t jhash_1word(uint32_t a, uint32_t initval) +{ + return jhash_3words(a, 0, 0, initval); +} |