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 * http://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 */
70 static 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; /* fall through */
90 case 11: c += (u32)k[10]<<16; /* fall through */
91 case 10: c += (u32)k[9]<<8; /* fall through */
92 case 9: c += k[8]; /* fall through */
93 case 8: b += (u32)k[7]<<24; /* fall through */
94 case 7: b += (u32)k[6]<<16; /* fall through */
95 case 6: b += (u32)k[5]<<8; /* fall through */
96 case 5: b += k[4]; /* fall through */
97 case 4: a += (u32)k[3]<<24; /* fall through */
98 case 3: a += (u32)k[2]<<16; /* fall through */
99 case 2: a += (u32)k[1]<<8; /* fall through */
100 case 1: a += k[0];
101 __jhash_final(a, b, c);
102 case 0: /* Nothing left to add */
103 break;
104 }
105
106 return c;
107 }
108
109 /* jhash2 - hash an array of u32's
110 * @k: the key which must be an array of u32's
111 * @length: the number of u32's in the key
112 * @initval: the previous hash, or an arbitray value
113 *
114 * Returns the hash value of the key.
115 */
116 static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
117 {
118 u32 a, b, c;
119
120 /* Set up the internal state */
121 a = b = c = JHASH_INITVAL + (length<<2) + initval;
122
123 /* Handle most of the key */
124 while (length > 3) {
125 a += k[0];
126 b += k[1];
127 c += k[2];
128 __jhash_mix(a, b, c);
129 length -= 3;
130 k += 3;
131 }
132
133 /* Handle the last 3 u32's */
134 switch (length) {
135 case 3: c += k[2]; /* fall through */
136 case 2: b += k[1]; /* fall through */
137 case 1: a += k[0];
138 __jhash_final(a, b, c);
139 case 0: /* Nothing left to add */
140 break;
141 }
142
143 return c;
144 }
145
146
147 /* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */
148 static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
149 {
150 a += initval;
151 b += initval;
152 c += initval;
153
154 __jhash_final(a, b, c);
155
156 return c;
157 }
158
159 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
160 {
161 return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2));
162 }
163
164 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
165 {
166 return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
167 }
168
169 static inline u32 jhash_1word(u32 a, u32 initval)
170 {
171 return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2));
172 }
173
174 #endif /* _LINUX_JHASH_H */