Subversion Repositories shark

Rev

Details | Last modification | View Log | RSS feed

Rev Author Line No. Line
422 giacomo 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
 */
44
static inline u32 jhash(void *key, u32 length, u32 initval)
45
{
46
        u32 a, b, c, len;
47
        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
 */
87
static inline u32 jhash2(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
 */
122
static 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
 
133
static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
134
{
135
        return jhash_3words(a, b, 0, initval);
136
}
137
 
138
static inline u32 jhash_1word(u32 a, u32 initval)
139
{
140
        return jhash_3words(a, 0, 0, initval);
141
}
142
 
143
#endif /* _LINUX_JHASH_H */