Merge lp:~tangent-org/libmemcached/1.0-build/ Build: jenkins-Libmemcached-187
[m6w6/libmemcached] / libhashkit / jenkins.cc
1 /* vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
2 *
3 * HashKit library
4 *
5 * Copyright (C) 2011-2012 Data Differential, http://datadifferential.com/
6 * Copyright (C) 2006-2009 Brian Aker All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions are
10 * met:
11 *
12 * * Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 *
15 * * Redistributions in binary form must reproduce the above
16 * copyright notice, this list of conditions and the following disclaimer
17 * in the documentation and/or other materials provided with the
18 * distribution.
19 *
20 * * The names of its contributors may not be used to endorse or
21 * promote products derived from this software without specific prior
22 * written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
25 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
26 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
27 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
28 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
29 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
30 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
34 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
35 *
36 */
37
38 /*
39 *
40 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
41 * code any way you wish, private, educational, or commercial. It's free.
42 * Use for hash table lookup, or anything where one collision in 2^^32 is
43 * acceptable. Do NOT use for cryptographic purposes.
44 * http://burtleburtle.net/bob/hash/index.html
45 *
46 * Modified by Brian Pontz for libmemcached
47 * TODO:
48 * Add big endian support
49 */
50
51 #include <libhashkit/common.h>
52
53 #define hashsize(n) ((uint32_t)1<<(n))
54 #define hashmask(n) (hashsize(n)-1)
55 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
56
57 #define mix(a,b,c) \
58 { \
59 a -= c; a ^= rot(c, 4); c += b; \
60 b -= a; b ^= rot(a, 6); a += c; \
61 c -= b; c ^= rot(b, 8); b += a; \
62 a -= c; a ^= rot(c,16); c += b; \
63 b -= a; b ^= rot(a,19); a += c; \
64 c -= b; c ^= rot(b, 4); b += a; \
65 }
66
67 #define final(a,b,c) \
68 { \
69 c ^= b; c -= rot(b,14); \
70 a ^= c; a -= rot(c,11); \
71 b ^= a; b -= rot(a,25); \
72 c ^= b; c -= rot(b,16); \
73 a ^= c; a -= rot(c,4); \
74 b ^= a; b -= rot(a,14); \
75 c ^= b; c -= rot(b,24); \
76 }
77
78 #define JENKINS_INITVAL 13
79
80 /*
81 jenkins_hash() -- hash a variable-length key into a 32-bit value
82 k : the key (the unaligned variable-length array of bytes)
83 length : the length of the key, counting by bytes
84 initval : can be any 4-byte value
85 Returns a 32-bit value. Every bit of the key affects every bit of
86 the return value. Two keys differing by one or two bits will have
87 totally different hash values.
88
89 The best hash table sizes are powers of 2. There is no need to do
90 mod a prime (mod is sooo slow!). If you need less than 32 bits,
91 use a bitmask. For example, if you need only 10 bits, do
92 h = (h & hashmask(10));
93 In which case, the hash table should have hashsize(10) elements.
94 */
95
96 uint32_t hashkit_jenkins(const char *key, size_t length, void *)
97 {
98 uint32_t a,b,c; /* internal state */
99 #ifndef WORDS_BIGENDIAN
100 union { const void *ptr; size_t i; } u;
101 u.ptr = key;
102 #endif
103
104 /* Set up the internal state */
105 a = b = c = 0xdeadbeef + ((uint32_t)length) + JENKINS_INITVAL;
106
107 #ifndef WORDS_BIGENDIAN
108 if ((u.i & 0x3) == 0)
109 {
110 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
111
112 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
113 while (length > 12)
114 {
115 a += k[0];
116 b += k[1];
117 c += k[2];
118 mix(a,b,c);
119 length -= 12;
120 k += 3;
121 }
122
123 /*----------------------------- handle the last (probably partial) block */
124 /*
125 * "k[2]&0xffffff" actually reads beyond the end of the string, but
126 * then masks off the part it's not allowed to read. Because the
127 * string is aligned, the masked-off tail is in the same word as the
128 * rest of the string. Every machine with memory protection I've seen
129 * does it on word boundaries, so is OK with this. But VALGRIND will
130 * still catch it and complain. The masking trick does make the hash
131 * noticably faster for short strings (like English words).
132 */
133 switch(length)
134 {
135 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
136 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
137 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
138 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
139 case 8 : b+=k[1]; a+=k[0]; break;
140 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
141 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
142 case 5 : b+=k[1]&0xff; a+=k[0]; break;
143 case 4 : a+=k[0]; break;
144 case 3 : a+=k[0]&0xffffff; break;
145 case 2 : a+=k[0]&0xffff; break;
146 case 1 : a+=k[0]&0xff; break;
147 case 0 : return c; /* zero length strings require no mixing */
148 default: return c;
149 }
150
151 }
152 else if ((u.i & 0x1) == 0)
153 {
154 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
155 const uint8_t *k8;
156
157 /*--------------- all but last block: aligned reads and different mixing */
158 while (length > 12)
159 {
160 a += k[0] + (((uint32_t)k[1])<<16);
161 b += k[2] + (((uint32_t)k[3])<<16);
162 c += k[4] + (((uint32_t)k[5])<<16);
163 mix(a,b,c);
164 length -= 12;
165 k += 6;
166 }
167
168 /*----------------------------- handle the last (probably partial) block */
169 k8 = (const uint8_t *)k;
170 switch(length)
171 {
172 case 12: c+=k[4]+(((uint32_t)k[5])<<16);
173 b+=k[2]+(((uint32_t)k[3])<<16);
174 a+=k[0]+(((uint32_t)k[1])<<16);
175 break;
176 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
177 case 10: c+=k[4];
178 b+=k[2]+(((uint32_t)k[3])<<16);
179 a+=k[0]+(((uint32_t)k[1])<<16);
180 break;
181 case 9 : c+=k8[8]; /* fall through */
182 case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
183 a+=k[0]+(((uint32_t)k[1])<<16);
184 break;
185 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
186 case 6 : b+=k[2];
187 a+=k[0]+(((uint32_t)k[1])<<16);
188 break;
189 case 5 : b+=k8[4]; /* fall through */
190 case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
191 break;
192 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
193 case 2 : a+=k[0];
194 break;
195 case 1 : a+=k8[0];
196 break;
197 case 0 : return c; /* zero length requires no mixing */
198 default: return c;
199 }
200
201 }
202 else
203 { /* need to read the key one byte at a time */
204 #endif /* little endian */
205 const uint8_t *k = (const uint8_t *)key;
206
207 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
208 while (length > 12)
209 {
210 a += k[0];
211 a += ((uint32_t)k[1])<<8;
212 a += ((uint32_t)k[2])<<16;
213 a += ((uint32_t)k[3])<<24;
214 b += k[4];
215 b += ((uint32_t)k[5])<<8;
216 b += ((uint32_t)k[6])<<16;
217 b += ((uint32_t)k[7])<<24;
218 c += k[8];
219 c += ((uint32_t)k[9])<<8;
220 c += ((uint32_t)k[10])<<16;
221 c += ((uint32_t)k[11])<<24;
222 mix(a,b,c);
223 length -= 12;
224 k += 12;
225 }
226
227 /*-------------------------------- last block: affect all 32 bits of (c) */
228 switch(length) /* all the case statements fall through */
229 {
230 case 12: c+=((uint32_t)k[11])<<24;
231 case 11: c+=((uint32_t)k[10])<<16;
232 case 10: c+=((uint32_t)k[9])<<8;
233 case 9 : c+=k[8];
234 case 8 : b+=((uint32_t)k[7])<<24;
235 case 7 : b+=((uint32_t)k[6])<<16;
236 case 6 : b+=((uint32_t)k[5])<<8;
237 case 5 : b+=k[4];
238 case 4 : a+=((uint32_t)k[3])<<24;
239 case 3 : a+=((uint32_t)k[2])<<16;
240 case 2 : a+=((uint32_t)k[1])<<8;
241 case 1 : a+=k[0];
242 break;
243 case 0 : return c;
244 default : return c;
245 }
246 #ifndef WORDS_BIGENDIAN
247 }
248 #endif
249
250 final(a,b,c);
251 return c;
252 }