Added srcdir includes so that the include files could be found in vpath builds.
[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 #ifdef BYTEORDER_LITTLE_ENDIAN
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 }
108
109 }
110 else if ((u.i & 0x1) == 0)
111 {
112 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
113 const uint8_t *k8;
114
115 /*--------------- all but last block: aligned reads and different mixing */
116 while (length > 12)
117 {
118 a += k[0] + (((uint32_t)k[1])<<16);
119 b += k[2] + (((uint32_t)k[3])<<16);
120 c += k[4] + (((uint32_t)k[5])<<16);
121 mix(a,b,c);
122 length -= 12;
123 k += 6;
124 }
125
126 /*----------------------------- handle the last (probably partial) block */
127 k8 = (const uint8_t *)k;
128 switch(length)
129 {
130 case 12: c+=k[4]+(((uint32_t)k[5])<<16);
131 b+=k[2]+(((uint32_t)k[3])<<16);
132 a+=k[0]+(((uint32_t)k[1])<<16);
133 break;
134 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
135 case 10: c+=k[4];
136 b+=k[2]+(((uint32_t)k[3])<<16);
137 a+=k[0]+(((uint32_t)k[1])<<16);
138 break;
139 case 9 : c+=k8[8]; /* fall through */
140 case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
141 a+=k[0]+(((uint32_t)k[1])<<16);
142 break;
143 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
144 case 6 : b+=k[2];
145 a+=k[0]+(((uint32_t)k[1])<<16);
146 break;
147 case 5 : b+=k8[4]; /* fall through */
148 case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
149 break;
150 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
151 case 2 : a+=k[0];
152 break;
153 case 1 : a+=k8[0];
154 break;
155 case 0 : return c; /* zero length requires no mixing */
156 }
157
158 }
159 else
160 { /* need to read the key one byte at a time */
161 #endif /* little endian */
162 const uint8_t *k = (const uint8_t *)key;
163
164 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
165 while (length > 12)
166 {
167 a += k[0];
168 a += ((uint32_t)k[1])<<8;
169 a += ((uint32_t)k[2])<<16;
170 a += ((uint32_t)k[3])<<24;
171 b += k[4];
172 b += ((uint32_t)k[5])<<8;
173 b += ((uint32_t)k[6])<<16;
174 b += ((uint32_t)k[7])<<24;
175 c += k[8];
176 c += ((uint32_t)k[9])<<8;
177 c += ((uint32_t)k[10])<<16;
178 c += ((uint32_t)k[11])<<24;
179 mix(a,b,c);
180 length -= 12;
181 k += 12;
182 }
183
184 /*-------------------------------- last block: affect all 32 bits of (c) */
185 switch(length) /* all the case statements fall through */
186 {
187 case 12: c+=((uint32_t)k[11])<<24;
188 case 11: c+=((uint32_t)k[10])<<16;
189 case 10: c+=((uint32_t)k[9])<<8;
190 case 9 : c+=k[8];
191 case 8 : b+=((uint32_t)k[7])<<24;
192 case 7 : b+=((uint32_t)k[6])<<16;
193 case 6 : b+=((uint32_t)k[5])<<8;
194 case 5 : b+=k[4];
195 case 4 : a+=((uint32_t)k[3])<<24;
196 case 3 : a+=((uint32_t)k[2])<<16;
197 case 2 : a+=((uint32_t)k[1])<<8;
198 case 1 : a+=k[0];
199 break;
200 case 0 : return c;
201 }
202 #ifdef BYTEORDER_LITTLE_ENDIAN
203 }
204 #endif
205
206 final(a,b,c);
207 return c;
208 }
209
210