Merge Monty
[m6w6/libmemcached] / libmemcached / jenkins_hash.c
1 /*
2 *
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
8 *
9 * Modified by Brian Pontz for libmemcached
10 * TODO:
11 * Add big endian support
12 */
13
14 #include "common.h"
15
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))))
19
20 #define mix(a,b,c) \
21 { \
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; \
28 }
29
30 #define final(a,b,c) \
31 { \
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); \
39 }
40
41 /*
42 jenkins_hash() -- hash a variable-length key into a 32-bit value
43 k : the key (the unaligned variable-length array of bytes)
44 length : the length of the key, counting by bytes
45 initval : can be any 4-byte value
46 Returns a 32-bit value. Every bit of the key affects every bit of
47 the return value. Two keys differing by one or two bits will have
48 totally different hash values.
49
50 The best hash table sizes are powers of 2. There is no need to do
51 mod a prime (mod is sooo slow!). If you need less than 32 bits,
52 use a bitmask. For example, if you need only 10 bits, do
53 h = (h & hashmask(10));
54 In which case, the hash table should have hashsize(10) elements.
55 */
56
57 uint32_t jenkins_hash(const void *key, size_t length, uint32_t initval)
58 {
59 uint32_t a,b,c; /* internal state */
60 union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */
61
62 /* Set up the internal state */
63 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
64
65 u.ptr = key;
66 #ifndef WORDS_BIGENDIAN
67 if ((u.i & 0x3) == 0)
68 {
69 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
70
71 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
72 while (length > 12)
73 {
74 a += k[0];
75 b += k[1];
76 c += k[2];
77 mix(a,b,c);
78 length -= 12;
79 k += 3;
80 }
81
82 /*----------------------------- handle the last (probably partial) block */
83 /*
84 * "k[2]&0xffffff" actually reads beyond the end of the string, but
85 * then masks off the part it's not allowed to read. Because the
86 * string is aligned, the masked-off tail is in the same word as the
87 * rest of the string. Every machine with memory protection I've seen
88 * does it on word boundaries, so is OK with this. But VALGRIND will
89 * still catch it and complain. The masking trick does make the hash
90 * noticably faster for short strings (like English words).
91 */
92 switch(length)
93 {
94 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
95 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
96 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
97 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
98 case 8 : b+=k[1]; a+=k[0]; break;
99 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
100 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
101 case 5 : b+=k[1]&0xff; a+=k[0]; break;
102 case 4 : a+=k[0]; break;
103 case 3 : a+=k[0]&0xffffff; break;
104 case 2 : a+=k[0]&0xffff; break;
105 case 1 : a+=k[0]&0xff; break;
106 case 0 : return c; /* zero length strings require no mixing */
107 default: return c;
108 }
109
110 }
111 else if ((u.i & 0x1) == 0)
112 {
113 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
114 const uint8_t *k8;
115
116 /*--------------- all but last block: aligned reads and different mixing */
117 while (length > 12)
118 {
119 a += k[0] + (((uint32_t)k[1])<<16);
120 b += k[2] + (((uint32_t)k[3])<<16);
121 c += k[4] + (((uint32_t)k[5])<<16);
122 mix(a,b,c);
123 length -= 12;
124 k += 6;
125 }
126
127 /*----------------------------- handle the last (probably partial) block */
128 k8 = (const uint8_t *)k;
129 switch(length)
130 {
131 case 12: c+=k[4]+(((uint32_t)k[5])<<16);
132 b+=k[2]+(((uint32_t)k[3])<<16);
133 a+=k[0]+(((uint32_t)k[1])<<16);
134 break;
135 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
136 case 10: c+=k[4];
137 b+=k[2]+(((uint32_t)k[3])<<16);
138 a+=k[0]+(((uint32_t)k[1])<<16);
139 break;
140 case 9 : c+=k8[8]; /* fall through */
141 case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
142 a+=k[0]+(((uint32_t)k[1])<<16);
143 break;
144 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
145 case 6 : b+=k[2];
146 a+=k[0]+(((uint32_t)k[1])<<16);
147 break;
148 case 5 : b+=k8[4]; /* fall through */
149 case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
150 break;
151 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
152 case 2 : a+=k[0];
153 break;
154 case 1 : a+=k8[0];
155 break;
156 case 0 : return c; /* zero length requires no mixing */
157 default: return c;
158 }
159
160 }
161 else
162 { /* need to read the key one byte at a time */
163 #endif /* little endian */
164 const uint8_t *k = (const uint8_t *)key;
165
166 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
167 while (length > 12)
168 {
169 a += k[0];
170 a += ((uint32_t)k[1])<<8;
171 a += ((uint32_t)k[2])<<16;
172 a += ((uint32_t)k[3])<<24;
173 b += k[4];
174 b += ((uint32_t)k[5])<<8;
175 b += ((uint32_t)k[6])<<16;
176 b += ((uint32_t)k[7])<<24;
177 c += k[8];
178 c += ((uint32_t)k[9])<<8;
179 c += ((uint32_t)k[10])<<16;
180 c += ((uint32_t)k[11])<<24;
181 mix(a,b,c);
182 length -= 12;
183 k += 12;
184 }
185
186 /*-------------------------------- last block: affect all 32 bits of (c) */
187 switch(length) /* all the case statements fall through */
188 {
189 case 12: c+=((uint32_t)k[11])<<24;
190 case 11: c+=((uint32_t)k[10])<<16;
191 case 10: c+=((uint32_t)k[9])<<8;
192 case 9 : c+=k[8];
193 case 8 : b+=((uint32_t)k[7])<<24;
194 case 7 : b+=((uint32_t)k[6])<<16;
195 case 6 : b+=((uint32_t)k[5])<<8;
196 case 5 : b+=k[4];
197 case 4 : a+=((uint32_t)k[3])<<24;
198 case 3 : a+=((uint32_t)k[2])<<16;
199 case 2 : a+=((uint32_t)k[1])<<8;
200 case 1 : a+=k[0];
201 break;
202 case 0 : return c;
203 default : return c;
204 }
205 #ifndef WORDS_BIGENDIAN
206 }
207 #endif
208
209 final(a,b,c);
210 return c;
211 }
212
213