From b9790b34c825e390c818044f6666f73beee1d373 Mon Sep 17 00:00:00 2001 From: paul Date: Fri, 9 Jul 2004 14:05:47 +0000 Subject: 2004-07-09 Paul Jakma * jhash.{c,h}: New files. Bob Jenkins' public domain hashing function, as implemented in linux kernel by David Miller. --- lib/jhash.c | 170 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 170 insertions(+) create mode 100644 lib/jhash.c (limited to 'lib/jhash.c') diff --git a/lib/jhash.c b/lib/jhash.c new file mode 100644 index 00000000..071fed6e --- /dev/null +++ b/lib/jhash.c @@ -0,0 +1,170 @@ +/* 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. + */ +u_int32_t +jhash (void *key, u_int32_t length, u_int32_t initval) +{ + u_int32_t a, b, c, len; + u_int8_t *k = key; + + len = length; + a = b = JHASH_GOLDEN_RATIO; + c = initval; + + while (len >= 12) + { + a += + (k[0] + ((u_int32_t) k[1] << 8) + ((u_int32_t) k[2] << 16) + + ((u_int32_t) k[3] << 24)); + b += + (k[4] + ((u_int32_t) k[5] << 8) + ((u_int32_t) k[6] << 16) + + ((u_int32_t) k[7] << 24)); + c += + (k[8] + ((u_int32_t) k[9] << 8) + ((u_int32_t) k[10] << 16) + + ((u_int32_t) k[11] << 24)); + + __jhash_mix (a, b, c); + + k += 12; + len -= 12; + } + + c += length; + switch (len) + { + case 11: + c += ((u_int32_t) k[10] << 24); + case 10: + c += ((u_int32_t) k[9] << 16); + case 9: + c += ((u_int32_t) k[8] << 8); + case 8: + b += ((u_int32_t) k[7] << 24); + case 7: + b += ((u_int32_t) k[6] << 16); + case 6: + b += ((u_int32_t) k[5] << 8); + case 5: + b += k[4]; + case 4: + a += ((u_int32_t) k[3] << 24); + case 3: + a += ((u_int32_t) k[2] << 16); + case 2: + a += ((u_int32_t) k[1] << 8); + case 1: + a += k[0]; + }; + + __jhash_mix (a, b, c); + + return c; +} + +/* A special optimized version that handles 1 or more of u_int32_ts. + * The length parameter here is the number of u_int32_ts in the key. + */ +u_int32_t +jhash2 (u_int32_t * k, u_int32_t length, u_int32_t initval) +{ + u_int32_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]; + 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. + */ +u_int32_t +jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval) +{ + a += JHASH_GOLDEN_RATIO; + b += JHASH_GOLDEN_RATIO; + c += initval; + + __jhash_mix (a, b, c); + + return c; +} + +u_int32_t +jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval) +{ + return jhash_3words (a, b, 0, initval); +} + +u_int32_t +jhash_1word (u_int32_t a, u_int32_t initval) +{ + return jhash_3words (a, 0, 0, initval); +} -- cgit v1.2.1