3 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
4 * code any way you wish, private, educational, or commercial. It's free.
5 * Use for hash table lookup, or anything where one collision in 2^^32 is
6 * acceptable. Do NOT use for cryptographic purposes.
7 * http://burtleburtle.net/bob/hash/index.html
9 * Modified by Brian Pontz for libmemcached
11 * Add big endian support
16 #define hashsize(n) ((uint32_t)1<<(n))
17 #define hashmask(n) (hashsize(n)-1)
18 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
22 a -= c; a ^= rot(c, 4); c += b; \
23 b -= a; b ^= rot(a, 6); a += c; \
24 c -= b; c ^= rot(b, 8); b += a; \
25 a -= c; a ^= rot(c,16); c += b; \
26 b -= a; b ^= rot(a,19); a += c; \
27 c -= b; c ^= rot(b, 4); b += a; \
30 #define final(a,b,c) \
32 c ^= b; c -= rot(b,14); \
33 a ^= c; a -= rot(c,11); \
34 b ^= a; b -= rot(a,25); \
35 c ^= b; c -= rot(b,16); \
36 a ^= c; a -= rot(c,4); \
37 b ^= a; b -= rot(a,14); \
38 c ^= b; c -= rot(b,24); \
41 #define JENKINS_INITVAL 13
44 jenkins_hash() -- hash a variable-length key into a 32-bit value
45 k : the key (the unaligned variable-length array of bytes)
46 length : the length of the key, counting by bytes
47 initval : can be any 4-byte value
48 Returns a 32-bit value. Every bit of the key affects every bit of
49 the return value. Two keys differing by one or two bits will have
50 totally different hash values.
52 The best hash table sizes are powers of 2. There is no need to do
53 mod a prime (mod is sooo slow!). If you need less than 32 bits,
54 use a bitmask. For example, if you need only 10 bits, do
55 h = (h & hashmask(10));
56 In which case, the hash table should have hashsize(10) elements.
59 uint32_t hashkit_jenkins(const char *key
, size_t length
, void *context
)
61 uint32_t a
,b
,c
; /* internal state */
62 union { const void *ptr
; size_t i
; } u
; /* needed for Mac Powerbook G4 */
65 /* Set up the internal state */
66 a
= b
= c
= 0xdeadbeef + ((uint32_t)length
) + JENKINS_INITVAL
;
69 #ifndef WORDS_BIGENDIAN
72 const uint32_t *k
= (const uint32_t *)key
; /* read 32-bit chunks */
74 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
85 /*----------------------------- handle the last (probably partial) block */
87 * "k[2]&0xffffff" actually reads beyond the end of the string, but
88 * then masks off the part it's not allowed to read. Because the
89 * string is aligned, the masked-off tail is in the same word as the
90 * rest of the string. Every machine with memory protection I've seen
91 * does it on word boundaries, so is OK with this. But VALGRIND will
92 * still catch it and complain. The masking trick does make the hash
93 * noticably faster for short strings (like English words).
97 case 12: c
+=k
[2]; b
+=k
[1]; a
+=k
[0]; break;
98 case 11: c
+=k
[2]&0xffffff; b
+=k
[1]; a
+=k
[0]; break;
99 case 10: c
+=k
[2]&0xffff; b
+=k
[1]; a
+=k
[0]; break;
100 case 9 : c
+=k
[2]&0xff; b
+=k
[1]; a
+=k
[0]; break;
101 case 8 : b
+=k
[1]; a
+=k
[0]; break;
102 case 7 : b
+=k
[1]&0xffffff; a
+=k
[0]; break;
103 case 6 : b
+=k
[1]&0xffff; a
+=k
[0]; break;
104 case 5 : b
+=k
[1]&0xff; a
+=k
[0]; break;
105 case 4 : a
+=k
[0]; break;
106 case 3 : a
+=k
[0]&0xffffff; break;
107 case 2 : a
+=k
[0]&0xffff; break;
108 case 1 : a
+=k
[0]&0xff; break;
109 case 0 : return c
; /* zero length strings require no mixing */
114 else if ((u
.i
& 0x1) == 0)
116 const uint16_t *k
= (const uint16_t *)key
; /* read 16-bit chunks */
119 /*--------------- all but last block: aligned reads and different mixing */
122 a
+= k
[0] + (((uint32_t)k
[1])<<16);
123 b
+= k
[2] + (((uint32_t)k
[3])<<16);
124 c
+= k
[4] + (((uint32_t)k
[5])<<16);
130 /*----------------------------- handle the last (probably partial) block */
131 k8
= (const uint8_t *)k
;
134 case 12: c
+=k
[4]+(((uint32_t)k
[5])<<16);
135 b
+=k
[2]+(((uint32_t)k
[3])<<16);
136 a
+=k
[0]+(((uint32_t)k
[1])<<16);
138 case 11: c
+=((uint32_t)k8
[10])<<16; /* fall through */
140 b
+=k
[2]+(((uint32_t)k
[3])<<16);
141 a
+=k
[0]+(((uint32_t)k
[1])<<16);
143 case 9 : c
+=k8
[8]; /* fall through */
144 case 8 : b
+=k
[2]+(((uint32_t)k
[3])<<16);
145 a
+=k
[0]+(((uint32_t)k
[1])<<16);
147 case 7 : b
+=((uint32_t)k8
[6])<<16; /* fall through */
149 a
+=k
[0]+(((uint32_t)k
[1])<<16);
151 case 5 : b
+=k8
[4]; /* fall through */
152 case 4 : a
+=k
[0]+(((uint32_t)k
[1])<<16);
154 case 3 : a
+=((uint32_t)k8
[2])<<16; /* fall through */
159 case 0 : return c
; /* zero length requires no mixing */
165 { /* need to read the key one byte at a time */
166 #endif /* little endian */
167 const uint8_t *k
= (const uint8_t *)key
;
169 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
173 a
+= ((uint32_t)k
[1])<<8;
174 a
+= ((uint32_t)k
[2])<<16;
175 a
+= ((uint32_t)k
[3])<<24;
177 b
+= ((uint32_t)k
[5])<<8;
178 b
+= ((uint32_t)k
[6])<<16;
179 b
+= ((uint32_t)k
[7])<<24;
181 c
+= ((uint32_t)k
[9])<<8;
182 c
+= ((uint32_t)k
[10])<<16;
183 c
+= ((uint32_t)k
[11])<<24;
189 /*-------------------------------- last block: affect all 32 bits of (c) */
190 switch(length
) /* all the case statements fall through */
192 case 12: c
+=((uint32_t)k
[11])<<24;
193 case 11: c
+=((uint32_t)k
[10])<<16;
194 case 10: c
+=((uint32_t)k
[9])<<8;
196 case 8 : b
+=((uint32_t)k
[7])<<24;
197 case 7 : b
+=((uint32_t)k
[6])<<16;
198 case 6 : b
+=((uint32_t)k
[5])<<8;
200 case 4 : a
+=((uint32_t)k
[3])<<24;
201 case 3 : a
+=((uint32_t)k
[2])<<16;
202 case 2 : a
+=((uint32_t)k
[1])<<8;
208 #ifndef WORDS_BIGENDIAN