jhash.h

  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@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 */
 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	/* 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 */
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: 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) */
149static 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
160static 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
165static 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
170static 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 */