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 arbitrary 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  */
jhash(const void * key,u32 length,u32 initval)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;	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 arbitrary value
114  *
115  * Returns the hash value of the key.
116  */
jhash2(const u32 * k,u32 length,u32 initval)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 */
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) */
__jhash_nwords(u32 a,u32 b,u32 c,u32 initval)150 static 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 
jhash_3words(u32 a,u32 b,u32 c,u32 initval)161 static 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 
jhash_2words(u32 a,u32 b,u32 initval)166 static 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 
jhash_1word(u32 a,u32 initval)171 static 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