7 * Example hash function.
9 * Copyright 2009-2012 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
11 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
12 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
14 * Permission is hereby granted to use or copy this program for any
15 * purpose, provided the above notices are retained on all copies.
16 * Permission to modify the code and to distribute modified code is
17 * granted, provided the above notices are retained, and a notice that
18 * the code was modified is included with the above copyright notice.
23 * Source: http://burtleburtle.net/bob/c/lookup3.c
24 * Originally Public Domain
27 #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
29 #define mix(a, b, c) \
31 a -= c; a ^= rot(c, 4); c += b; \
32 b -= a; b ^= rot(a, 6); a += c; \
33 c -= b; c ^= rot(b, 8); b += a; \
34 a -= c; a ^= rot(c, 16); c += b; \
35 b -= a; b ^= rot(a, 19); a += c; \
36 c -= b; c ^= rot(b, 4); b += a; \
39 #define final(a, b, c) \
41 c ^= b; c -= rot(b, 14); \
42 a ^= c; a -= rot(c, 11); \
43 b ^= a; b -= rot(a, 25); \
44 c ^= b; c -= rot(b, 16); \
45 a ^= c; a -= rot(c, 4); \
46 b ^= a; b -= rot(a, 14); \
47 c ^= b; c -= rot(b, 24); \
50 #if (BYTE_ORDER == LITTLE_ENDIAN)
51 #define HASH_LITTLE_ENDIAN 1
53 #define HASH_LITTLE_ENDIAN 0
58 * hashlittle() -- hash a variable-length key into a 32-bit value
59 * k : the key (the unaligned variable-length array of bytes)
60 * length : the length of the key, counting by bytes
61 * initval : can be any 4-byte value
62 * Returns a 32-bit value. Every bit of the key affects every bit of
63 * the return value. Two keys differing by one or two bits will have
64 * totally different hash values.
66 * The best hash table sizes are powers of 2. There is no need to do
67 * mod a prime (mod is sooo slow!). If you need less than 32 bits,
68 * use a bitmask. For example, if you need only 10 bits, do
69 * h = (h & hashmask(10));
70 * In which case, the hash table should have hashsize(10) elements.
72 * If you are hashing n strings (uint8_t **)k, do it like this:
73 * for (i = 0, h = 0; i < n; ++i) h = hashlittle(k[i], len[i], h);
75 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
76 * code any way you wish, private, educational, or commercial. It's free.
78 * Use for hash table lookup, or anything where one collision in 2^^32 is
79 * acceptable. Do NOT use for cryptographic purposes.
82 uint32_t hashlittle(const void *key
, size_t length
, uint32_t initval
)
84 uint32_t a
, b
, c
; /* internal state */
90 /* Set up the internal state */
91 a
= b
= c
= 0xdeadbeef + ((uint32_t)length
) + initval
;
94 if (HASH_LITTLE_ENDIAN
&& ((u
.i
& 0x3) == 0)) {
95 const uint32_t *k
= (const uint32_t *) key
; /* read 32-bit chunks */
97 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
107 /*----------------------------- handle the last (probably partial) block */
109 * "k[2]&0xffffff" actually reads beyond the end of the string, but
110 * then masks off the part it's not allowed to read. Because the
111 * string is aligned, the masked-off tail is in the same word as the
112 * rest of the string. Every machine with memory protection I've seen
113 * does it on word boundaries, so is OK with this. But VALGRIND will
114 * still catch it and complain. The masking trick does make the hash
115 * noticably faster for short strings (like English words).
120 case 12: c
+=k
[2]; b
+=k
[1]; a
+=k
[0]; break;
121 case 11: c
+=k
[2]&0xffffff; b
+=k
[1]; a
+=k
[0]; break;
122 case 10: c
+=k
[2]&0xffff; b
+=k
[1]; a
+=k
[0]; break;
123 case 9 : c
+=k
[2]&0xff; b
+=k
[1]; a
+=k
[0]; break;
124 case 8 : b
+=k
[1]; a
+=k
[0]; break;
125 case 7 : b
+=k
[1]&0xffffff; a
+=k
[0]; break;
126 case 6 : b
+=k
[1]&0xffff; a
+=k
[0]; break;
127 case 5 : b
+=k
[1]&0xff; a
+=k
[0]; break;
128 case 4 : a
+=k
[0]; break;
129 case 3 : a
+=k
[0]&0xffffff; break;
130 case 2 : a
+=k
[0]&0xffff; break;
131 case 1 : a
+=k
[0]&0xff; break;
132 case 0 : return c
; /* zero length strings require no mixing */
135 #else /* make valgrind happy */
139 k8
= (const uint8_t *) k
;
141 case 12: c
+=k
[2]; b
+=k
[1]; a
+=k
[0]; break;
142 case 11: c
+=((uint32_t) k8
[10])<<16; /* fall through */
143 case 10: c
+=((uint32_t) k8
[9])<<8; /* fall through */
144 case 9 : c
+=k8
[8]; /* fall through */
145 case 8 : b
+=k
[1]; a
+=k
[0]; break;
146 case 7 : b
+=((uint32_t) k8
[6])<<16; /* fall through */
147 case 6 : b
+=((uint32_t) k8
[5])<<8; /* fall through */
148 case 5 : b
+=k8
[4]; /* fall through */
149 case 4 : a
+=k
[0]; break;
150 case 3 : a
+=((uint32_t) k8
[2])<<16; /* fall through */
151 case 2 : a
+=((uint32_t) k8
[1])<<8; /* fall through */
152 case 1 : a
+=k8
[0]; break;
156 #endif /* !valgrind */
158 } else if (HASH_LITTLE_ENDIAN
&& ((u
.i
& 0x1) == 0)) {
159 const uint16_t *k
= (const uint16_t *) key
; /* read 16-bit chunks */
162 /*--------------- all but last block: aligned reads and different mixing */
165 a
+= k
[0] + (((uint32_t) k
[1])<<16);
166 b
+= k
[2] + (((uint32_t) k
[3])<<16);
167 c
+= k
[4] + (((uint32_t) k
[5])<<16);
173 /*----------------------------- handle the last (probably partial) block */
174 k8
= (const uint8_t *) k
;
177 case 12: c
+=k
[4]+(((uint32_t) k
[5])<<16);
178 b
+=k
[2]+(((uint32_t) k
[3])<<16);
179 a
+=k
[0]+(((uint32_t) k
[1])<<16);
181 case 11: c
+=((uint32_t) k8
[10])<<16; /* fall through */
183 b
+=k
[2]+(((uint32_t) k
[3])<<16);
184 a
+=k
[0]+(((uint32_t) k
[1])<<16);
186 case 9 : c
+=k8
[8]; /* fall through */
187 case 8 : b
+=k
[2]+(((uint32_t) k
[3])<<16);
188 a
+=k
[0]+(((uint32_t) k
[1])<<16);
190 case 7 : b
+=((uint32_t) k8
[6])<<16; /* fall through */
192 a
+=k
[0]+(((uint32_t) k
[1])<<16);
194 case 5 : b
+=k8
[4]; /* fall through */
195 case 4 : a
+=k
[0]+(((uint32_t) k
[1])<<16);
197 case 3 : a
+=((uint32_t) k8
[2])<<16; /* fall through */
202 case 0 : return c
; /* zero length requires no mixing */
205 } else { /* need to read the key one byte at a time */
206 const uint8_t *k
= (const uint8_t *)key
;
208 /*--------------- all but the last block: affect some 32 bits of (a, b, c) */
209 while (length
> 12) {
211 a
+= ((uint32_t) k
[1])<<8;
212 a
+= ((uint32_t) k
[2])<<16;
213 a
+= ((uint32_t) k
[3])<<24;
215 b
+= ((uint32_t) k
[5])<<8;
216 b
+= ((uint32_t) k
[6])<<16;
217 b
+= ((uint32_t) k
[7])<<24;
219 c
+= ((uint32_t) k
[9])<<8;
220 c
+= ((uint32_t) k
[10])<<16;
221 c
+= ((uint32_t) k
[11])<<24;
227 /*-------------------------------- last block: affect all 32 bits of (c) */
228 switch (length
) { /* all the case statements fall through */
229 case 12: c
+=((uint32_t) k
[11])<<24; /* fall through */
230 case 11: c
+=((uint32_t) k
[10])<<16; /* fall through */
231 case 10: c
+=((uint32_t) k
[9])<<8; /* fall through */
232 case 9 : c
+=k
[8]; /* fall through */
233 case 8 : b
+=((uint32_t) k
[7])<<24; /* fall through */
234 case 7 : b
+=((uint32_t) k
[6])<<16; /* fall through */
235 case 6 : b
+=((uint32_t) k
[5])<<8; /* fall through */
236 case 5 : b
+=k
[4]; /* fall through */
237 case 4 : a
+=((uint32_t) k
[3])<<24; /* fall through */
238 case 3 : a
+=((uint32_t) k
[2])<<16; /* fall through */
239 case 2 : a
+=((uint32_t) k
[1])<<8; /* fall through */
251 uint32_t jhash(const void *key
, size_t length
, uint32_t seed
)
253 return hashlittle(key
, length
, seed
);
256 #endif /* _JHASH_H */
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