diff options
author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-17 02:20:36 +0400 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-17 02:20:36 +0400 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /include/linux/jhash.h |
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Diffstat (limited to 'include/linux/jhash.h')
-rw-r--r-- | include/linux/jhash.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/include/linux/jhash.h b/include/linux/jhash.h new file mode 100644 index 000000000000..82c7ae412eec --- /dev/null +++ b/include/linux/jhash.h @@ -0,0 +1,143 @@ +#ifndef _LINUX_JHASH_H +#define _LINUX_JHASH_H + +/* 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 + */ + +/* 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 golden ration: an arbitrary value */ +#define JHASH_GOLDEN_RATIO 0x9e3779b9 + +/* The most generic version, hashes an arbitrary sequence + * of bytes. No alignment or length assumptions are made about + * the input key. + */ +static inline u32 jhash(const void *key, u32 length, u32 initval) +{ + u32 a, b, c, len; + const u8 *k = key; + + len = length; + a = b = JHASH_GOLDEN_RATIO; + c = initval; + + while (len >= 12) { + a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24)); + b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24)); + c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24)); + + __jhash_mix(a,b,c); + + k += 12; + len -= 12; + } + + c += length; + switch (len) { + case 11: c += ((u32)k[10]<<24); + case 10: c += ((u32)k[9]<<16); + case 9 : c += ((u32)k[8]<<8); + case 8 : b += ((u32)k[7]<<24); + case 7 : b += ((u32)k[6]<<16); + case 6 : b += ((u32)k[5]<<8); + case 5 : b += k[4]; + case 4 : a += ((u32)k[3]<<24); + case 3 : a += ((u32)k[2]<<16); + case 2 : a += ((u32)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 u32s. + * The length parameter here is the number of u32s in the key. + */ +static inline u32 jhash2(u32 *k, u32 length, u32 initval) +{ + u32 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. + */ +static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) +{ + a += JHASH_GOLDEN_RATIO; + b += JHASH_GOLDEN_RATIO; + c += initval; + + __jhash_mix(a, b, c); + + return c; +} + +static inline u32 jhash_2words(u32 a, u32 b, u32 initval) +{ + return jhash_3words(a, b, 0, initval); +} + +static inline u32 jhash_1word(u32 a, u32 initval) +{ + return jhash_3words(a, 0, 0, initval); +} + +#endif /* _LINUX_JHASH_H */ |