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TOMOYO Linux Cross Reference
Linux/include/linux/jhash.h

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  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@blackhole.kfki.hu)
 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         /* All the case statements fall through */
 89         switch (length) {
 90         case 12: c += (u32)k[11]<<24;
 91         case 11: c += (u32)k[10]<<16;
 92         case 10: c += (u32)k[9]<<8;
 93         case 9:  c += k[8];
 94         case 8:  b += (u32)k[7]<<24;
 95         case 7:  b += (u32)k[6]<<16;
 96         case 6:  b += (u32)k[5]<<8;
 97         case 5:  b += k[4];
 98         case 4:  a += (u32)k[3]<<24;
 99         case 3:  a += (u32)k[2]<<16;
100         case 2:  a += (u32)k[1]<<8;
101         case 1:  a += k[0];
102                  __jhash_final(a, b, c);
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  */
117 static 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: all the case statements fall through */
135         switch (length) {
136         case 3: c += k[2];
137         case 2: b += k[1];
138         case 1: a += k[0];
139                 __jhash_final(a, b, c);
140         case 0: /* Nothing left to add */
141                 break;
142         }
143 
144         return c;
145 }
146 
147 
148 /* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */
149 static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
150 {
151         a += initval;
152         b += initval;
153         c += initval;
154 
155         __jhash_final(a, b, c);
156 
157         return c;
158 }
159 
160 static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
161 {
162         return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2));
163 }
164 
165 static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
166 {
167         return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
168 }
169 
170 static inline u32 jhash_1word(u32 a, u32 initval)
171 {
172         return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2));
173 }
174 
175 #endif /* _LINUX_JHASH_H */
176 

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