1 #ifndef _LINUX_JHASH_H_
2 #define _LINUX_JHASH_H_
6 /* jhash.h: Jenkins hash support.
8 * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
10 * http://burtleburtle.net/bob/hash/
12 * These are the credits from Bob's sources:
14 * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
15 * hash(), hash2(), hash3, and mix() are externally useful functions.
16 * Routines to test the hash are included if SELF_TEST is defined.
17 * You can use this free for any purpose. It has no warranty.
19 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
21 * I've modified Bob's hash to be useful in the Linux kernel, and
22 * any bugs present are surely my fault. -DaveM
27 /* NOTE: Arguments are modified. */
28 #define __jhash_mix(a, b, c) \
30 a -= b; a -= c; a ^= (c>>13); \
31 b -= c; b -= a; b ^= (a<<8); \
32 c -= a; c -= b; c ^= (b>>13); \
33 a -= b; a -= c; a ^= (c>>12); \
34 b -= c; b -= a; b ^= (a<<16); \
35 c -= a; c -= b; c ^= (b>>5); \
36 a -= b; a -= c; a ^= (c>>3); \
37 b -= c; b -= a; b ^= (a<<10); \
38 c -= a; c -= b; c ^= (b>>15); \
41 /* The golden ration: an arbitrary value */
42 #define JHASH_GOLDEN_RATIO 0x9e3779b9
44 /* The most generic version, hashes an arbitrary sequence
45 * of bytes. No alignment or length assumptions are made about
48 static inline u32 jhash(const void *key, u32 length, u32 initval)
54 a = b = JHASH_GOLDEN_RATIO;
58 a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
59 b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
60 c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
70 case 11: c += ((u32)k[10]<<24);
71 case 10: c += ((u32)k[9]<<16);
72 case 9 : c += ((u32)k[8]<<8);
73 case 8 : b += ((u32)k[7]<<24);
74 case 7 : b += ((u32)k[6]<<16);
75 case 6 : b += ((u32)k[5]<<8);
77 case 4 : a += ((u32)k[3]<<24);
78 case 3 : a += ((u32)k[2]<<16);
79 case 2 : a += ((u32)k[1]<<8);
88 /* A special optimized version that handles 1 or more of u32s.
89 * The length parameter here is the number of u32s in the key.
91 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
95 a = b = JHASH_GOLDEN_RATIO;
103 __jhash_mix(a, b, c);
120 /* A special ultra-optimized versions that knows they are hashing exactly
123 * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
124 * done at the end is not done here.
126 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
128 a += JHASH_GOLDEN_RATIO;
129 b += JHASH_GOLDEN_RATIO;
132 __jhash_mix(a, b, c);
137 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
139 return jhash_3words(a, b, 0, initval);
142 static inline u32 jhash_1word(u32 a, u32 initval)
144 return jhash_3words(a, 0, 0, initval);
147 #endif /* _LINUX_JHASH_H_ */