-
Notifications
You must be signed in to change notification settings - Fork 5
/
jhash.h
157 lines (136 loc) · 3.97 KB
/
jhash.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
#ifndef _LINUX_JHASH_H
#define _LINUX_JHASH_H
/* jhash.h: Jenkins hash support.
*
* Copyright (C) 2006. Bob Jenkins ([email protected])
*
* http://burtleburtle.net/bob/hash/
*
* These are the credits from Bob's sources:
*
* lookup3.c, by Bob Jenkins, May 2006, Public Domain.
*
* These are functions for producing 32-bit hashes for hash table lookup.
* hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
* 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's in
* the public domain. It has no warranty.
*
* Copyright (C) 2009 Jozsef Kadlecsik ([email protected])
*
* I've modified Bob's hash to be useful in the Linux kernel, and
* any bugs present are my fault. Jozsef
*/
#define __rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
/* __jhash_mix - mix 3 32-bit values reversibly. */
#define __jhash_mix(a,b,c) \
{ \
a -= c; a ^= __rot(c, 4); c += b; \
b -= a; b ^= __rot(a, 6); a += c; \
c -= b; c ^= __rot(b, 8); b += a; \
a -= c; a ^= __rot(c,16); c += b; \
b -= a; b ^= __rot(a,19); a += c; \
c -= b; c ^= __rot(b, 4); b += a; \
}
/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
#define __jhash_final(a,b,c) \
{ \
c ^= b; c -= __rot(b,14); \
a ^= c; a -= __rot(c,11); \
b ^= a; b -= __rot(a,25); \
c ^= b; c -= __rot(b,16); \
a ^= c; a -= __rot(c,4); \
b ^= a; b -= __rot(a,14); \
c ^= b; c -= __rot(b,24); \
}
/* The golden ration: an arbitrary value */
#define JHASH_GOLDEN_RATIO 0xdeadbeef
/* The most generic version, hashes an arbitrary sequence
* of bytes. No alignment or length assumptions are made about
* the input key. The result depends on endianness.
*/
static inline u32 jhash(const void *key, u32 length, u32 initval)
{
u32 a,b,c;
const u8 *k = key;
/* Set up the internal state */
a = b = c = JHASH_GOLDEN_RATIO + length + initval;
/* all but the last block: affect some 32 bits of (a,b,c) */
while (length > 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);
length -= 12;
k += 12;
}
/* last block: affect all 32 bits of (c) */
/* all the case statements fall through */
switch (length) {
case 12: c += (u32)k[11]<<24;
case 11: c += (u32)k[10]<<16;
case 10: c += (u32)k[9]<<8;
case 9 : c += k[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_final(a, b, c);
case 0 :
break;
}
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;
/* Set up the internal state */
a = b = c = JHASH_GOLDEN_RATIO + (length<<2) + initval;
/* handle most of the key */
while (length > 3) {
a += k[0];
b += k[1];
c += k[2];
__jhash_mix(a, b, c);
length -= 3;
k += 3;
}
/* handle the last 3 u32's */
/* all the case statements fall through */
switch (length) {
case 3: c += k[2];
case 2: b += k[1];
case 1: a += k[0];
__jhash_final(a, b, c);
case 0: /* case 0: nothing left to add */
break;
}
return c;
}
/* A special ultra-optimized versions that knows they are hashing exactly
* 3, 2 or 1 word(s).
*/
static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
{
a += JHASH_GOLDEN_RATIO + initval;
b += JHASH_GOLDEN_RATIO + initval;
c += JHASH_GOLDEN_RATIO + initval;
__jhash_final(a, b, c);
return c;
}
static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
return jhash_3words(0, a, b, initval);
}
static inline u32 jhash_1word(u32 a, u32 initval)
{
return jhash_3words(0, 0, a, initval);
}
#endif /* _LINUX_JHASH_H */