1#ifndef _LINUX_JHASH_H
2#define _LINUX_JHASH_H
3
4/* jhash.h: Jenkins hash support.
5 *
6 * Copyright (C) 2006. Bob Jenkins (bob_jenkins@burtleburtle.net)
7 *
8 * https://burtleburtle.net/bob/hash/
9 *
10 * These are the credits from Bob's sources:
11 *
12 * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
13 *
14 * These are functions for producing 32-bit hashes for hash table lookup.
15 * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
16 * are externally useful functions. Routines to test the hash are included
17 * if SELF_TEST is defined. You can use this free for any purpose. It's in
18 * the public domain. It has no warranty.
19 *
20 * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@netfilter.org)
21 *
22 * I've modified Bob's hash to be useful in the Linux kernel, and
23 * any bugs present are my fault.
24 * Jozsef
25 */
26#include <linux/bitops.h>
27#include <linux/unaligned/packed_struct.h>
28
29/* Best hash sizes are of power of two */
30#define jhash_size(n) ((u32)1<<(n))
31/* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
32#define jhash_mask(n) (jhash_size(n)-1)
33
34/* __jhash_mix -- mix 3 32-bit values reversibly. */
35#define __jhash_mix(a, b, c) \
36{ \
37 a -= c; a ^= rol32(c, 4); c += b; \
38 b -= a; b ^= rol32(a, 6); a += c; \
39 c -= b; c ^= rol32(b, 8); b += a; \
40 a -= c; a ^= rol32(c, 16); c += b; \
41 b -= a; b ^= rol32(a, 19); a += c; \
42 c -= b; c ^= rol32(b, 4); b += a; \
43}
44
45/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
46#define __jhash_final(a, b, c) \
47{ \
48 c ^= b; c -= rol32(b, 14); \
49 a ^= c; a -= rol32(c, 11); \
50 b ^= a; b -= rol32(a, 25); \
51 c ^= b; c -= rol32(b, 16); \
52 a ^= c; a -= rol32(c, 4); \
53 b ^= a; b -= rol32(a, 14); \
54 c ^= b; c -= rol32(b, 24); \
55}
56
57/* An arbitrary initial parameter */
58#define JHASH_INITVAL 0xdeadbeef
59
60/* jhash - hash an arbitrary key
61 * @k: sequence of bytes as key
62 * @length: the length of the key
63 * @initval: the previous hash, or an arbitray value
64 *
65 * The generic version, hashes an arbitrary sequence of bytes.
66 * No alignment or length assumptions are made about the input key.
67 *
68 * Returns the hash value of the key. The result depends on endianness.
69 */
70static inline u32 jhash(const void *key, u32 length, u32 initval)
71{
72 u32 a, b, c;
73 const u8 *k = key;
74
75 /* Set up the internal state */
76 a = b = c = JHASH_INITVAL + length + initval;
77
78 /* All but the last block: affect some 32 bits of (a,b,c) */
79 while (length > 12) {
80 a += __get_unaligned_cpu32(k);
81 b += __get_unaligned_cpu32(k + 4);
82 c += __get_unaligned_cpu32(k + 8);
83 __jhash_mix(a, b, c);
84 length -= 12;
85 k += 12;
86 }
87 /* Last block: affect all 32 bits of (c) */
88 switch (length) {
89 case 12: c += (u32)k[11]<<24; fallthrough;
90 case 11: c += (u32)k[10]<<16; fallthrough;
91 case 10: c += (u32)k[9]<<8; fallthrough;
92 case 9: c += k[8]; fallthrough;
93 case 8: b += (u32)k[7]<<24; fallthrough;
94 case 7: b += (u32)k[6]<<16; fallthrough;
95 case 6: b += (u32)k[5]<<8; fallthrough;
96 case 5: b += k[4]; fallthrough;
97 case 4: a += (u32)k[3]<<24; fallthrough;
98 case 3: a += (u32)k[2]<<16; fallthrough;
99 case 2: a += (u32)k[1]<<8; fallthrough;
100 case 1: a += k[0];
101 __jhash_final(a, b, c);
102 break;
103 case 0: /* Nothing left to add */
104 break;
105 }
106
107 return c;
108}
109
110/* jhash2 - hash an array of u32's
111 * @k: the key which must be an array of u32's
112 * @length: the number of u32's in the key
113 * @initval: the previous hash, or an arbitray value
114 *
115 * Returns the hash value of the key.
116 */
117static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
118{
119 u32 a, b, c;
120
121 /* Set up the internal state */
122 a = b = c = JHASH_INITVAL + (length<<2) + initval;
123
124 /* Handle most of the key */
125 while (length > 3) {
126 a += k[0];
127 b += k[1];
128 c += k[2];
129 __jhash_mix(a, b, c);
130 length -= 3;
131 k += 3;
132 }
133
134 /* Handle the last 3 u32's */
135 switch (length) {
136 case 3: c += k[2]; fallthrough;
137 case 2: b += k[1]; fallthrough;
138 case 1: a += k[0];
139 __jhash_final(a, b, c);
140 break;
141 case 0: /* Nothing left to add */
142 break;
143 }
144
145 return c;
146}
147
148
149/* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */
150static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
151{
152 a += initval;
153 b += initval;
154 c += initval;
155
156 __jhash_final(a, b, c);
157
158 return c;
159}
160
161static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
162{
163 return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2));
164}
165
166static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
167{
168 return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
169}
170
171static inline u32 jhash_1word(u32 a, u32 initval)
172{
173 return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2));
174}
175
176#endif /* _LINUX_JHASH_H */
177

source code of linux/include/linux/jhash.h