1#ifndef _LINUX_JHASH_H
2#define _LINUX_JHASH_H
3
4/* jhash.h: Jenkins hash support.
5 *
6 * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
7 *
8 * http://burtleburtle.net/bob/hash/
9 *
10 * These are the credits from Bob's sources:
11 *
12 * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
13 * hash(), hash2(), hash3, and mix() are externally useful functions.
14 * Routines to test the hash are included if SELF_TEST is defined.
15 * You can use this free for any purpose.  It has no warranty.
16 *
17 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
18 *
19 * I've modified Bob's hash to be useful in the Linux kernel, and
20 * any bugs present are surely my fault.  -DaveM
21 */
22
23/* NOTE: Arguments are modified. */
24#define __jhash_mix(a, b, c) \
25{ \
26  a -= b; a -= c; a ^= (c>>13); \
27  b -= c; b -= a; b ^= (a<<8); \
28  c -= a; c -= b; c ^= (b>>13); \
29  a -= b; a -= c; a ^= (c>>12);  \
30  b -= c; b -= a; b ^= (a<<16); \
31  c -= a; c -= b; c ^= (b>>5); \
32  a -= b; a -= c; a ^= (c>>3);  \
33  b -= c; b -= a; b ^= (a<<10); \
34  c -= a; c -= b; c ^= (b>>15); \
35}
36
37/* The golden ration: an arbitrary value */
38#define JHASH_GOLDEN_RATIO	0x9e3779b9
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 */
44static inline u32 jhash(const void *key, u32 length, u32 initval)
45{
46	u32 a, b, c, len;
47	const u8 *k = key;
48
49	len = length;
50	a = b = JHASH_GOLDEN_RATIO;
51	c = initval;
52
53	while (len >= 12) {
54		a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
55		b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
56		c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
57
58		__jhash_mix(a,b,c);
59
60		k += 12;
61		len -= 12;
62	}
63
64	c += length;
65	switch (len) {
66	case 11: c += ((u32)k[10]<<24);
67	case 10: c += ((u32)k[9]<<16);
68	case 9 : c += ((u32)k[8]<<8);
69	case 8 : b += ((u32)k[7]<<24);
70	case 7 : b += ((u32)k[6]<<16);
71	case 6 : b += ((u32)k[5]<<8);
72	case 5 : b += k[4];
73	case 4 : a += ((u32)k[3]<<24);
74	case 3 : a += ((u32)k[2]<<16);
75	case 2 : a += ((u32)k[1]<<8);
76	case 1 : a += k[0];
77	};
78
79	__jhash_mix(a,b,c);
80
81	return c;
82}
83
84/* A special optimized version that handles 1 or more of u32s.
85 * The length parameter here is the number of u32s in the key.
86 */
87static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
88{
89	u32 a, b, c, len;
90
91	a = b = JHASH_GOLDEN_RATIO;
92	c = initval;
93	len = length;
94
95	while (len >= 3) {
96		a += k[0];
97		b += k[1];
98		c += k[2];
99		__jhash_mix(a, b, c);
100		k += 3; len -= 3;
101	}
102
103	c += length * 4;
104
105	switch (len) {
106	case 2 : b += k[1];
107	case 1 : a += k[0];
108	};
109
110	__jhash_mix(a,b,c);
111
112	return c;
113}
114
115
116/* A special ultra-optimized versions that knows they are hashing exactly
117 * 3, 2 or 1 word(s).
118 *
119 * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
120 *       done at the end is not done here.
121 */
122static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
123{
124	a += JHASH_GOLDEN_RATIO;
125	b += JHASH_GOLDEN_RATIO;
126	c += initval;
127
128	__jhash_mix(a, b, c);
129
130	return c;
131}
132
133static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
134{
135	return jhash_3words(a, b, 0, initval);
136}
137
138static inline u32 jhash_1word(u32 a, u32 initval)
139{
140	return jhash_3words(a, 0, 0, initval);
141}
142
143#endif /* _LINUX_JHASH_H */
144