Revert "Remove useless const qualifier"
[lttng-ust.git] / liblttng-ust / jhash.h
1 /*
2 * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 *
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation;
7 * version 2.1 of the License.
8 *
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Lesser General Public License for more details.
13 *
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with this library; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17 */
18
19 #include <urcu/compiler.h>
20 #include <lttng/ust-endian.h>
21
22 /*
23 * Hash function
24 * Source: http://burtleburtle.net/bob/c/lookup3.c
25 * Originally Public Domain
26 */
27
28 #define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
29
30 #define mix(a, b, c) \
31 do { \
32 a -= c; a ^= rot(c, 4); c += b; \
33 b -= a; b ^= rot(a, 6); a += c; \
34 c -= b; c ^= rot(b, 8); b += a; \
35 a -= c; a ^= rot(c, 16); c += b; \
36 b -= a; b ^= rot(a, 19); a += c; \
37 c -= b; c ^= rot(b, 4); b += a; \
38 } while (0)
39
40 #define final(a, b, c) \
41 { \
42 c ^= b; c -= rot(b, 14); \
43 a ^= c; a -= rot(c, 11); \
44 b ^= a; b -= rot(a, 25); \
45 c ^= b; c -= rot(b, 16); \
46 a ^= c; a -= rot(c, 4);\
47 b ^= a; b -= rot(a, 14); \
48 c ^= b; c -= rot(b, 24); \
49 }
50
51 #if (BYTE_ORDER == LITTLE_ENDIAN)
52 #define HASH_LITTLE_ENDIAN 1
53 #else
54 #define HASH_LITTLE_ENDIAN 0
55 #endif
56
57 /*
58 *
59 * hashlittle() -- hash a variable-length key into a 32-bit value
60 * k : the key (the unaligned variable-length array of bytes)
61 * length : the length of the key, counting by bytes
62 * initval : can be any 4-byte value
63 * Returns a 32-bit value. Every bit of the key affects every bit of
64 * the return value. Two keys differing by one or two bits will have
65 * totally different hash values.
66 *
67 * The best hash table sizes are powers of 2. There is no need to do
68 * mod a prime (mod is sooo slow!). If you need less than 32 bits,
69 * use a bitmask. For example, if you need only 10 bits, do
70 * h = (h & hashmask(10));
71 * In which case, the hash table should have hashsize(10) elements.
72 *
73 * If you are hashing n strings (uint8_t **)k, do it like this:
74 * for (i = 0, h = 0; i < n; ++i) h = hashlittle(k[i], len[i], h);
75 *
76 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
77 * code any way you wish, private, educational, or commercial. It's free.
78 *
79 * Use for hash table lookup, or anything where one collision in 2^^32 is
80 * acceptable. Do NOT use for cryptographic purposes.
81 */
82 static
83 uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
84 {
85 uint32_t a, b, c; /* internal state */
86 union {
87 const void *ptr;
88 size_t i;
89 } u;
90
91 /* Set up the internal state */
92 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
93
94 u.ptr = key;
95 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
96 const uint32_t *k = (const uint32_t *) key; /* read 32-bit chunks */
97
98 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
99 while (length > 12) {
100 a += k[0];
101 b += k[1];
102 c += k[2];
103 mix(a, b, c);
104 length -= 12;
105 k += 3;
106 }
107
108 /*----------------------------- handle the last (probably partial) block */
109 /*
110 * "k[2]&0xffffff" actually reads beyond the end of the string, but
111 * then masks off the part it's not allowed to read. Because the
112 * string is aligned, the masked-off tail is in the same word as the
113 * rest of the string. Every machine with memory protection I've seen
114 * does it on word boundaries, so is OK with this. But VALGRIND will
115 * still catch it and complain. The masking trick does make the hash
116 * noticably faster for short strings (like English words).
117 */
118 #ifndef VALGRIND
119
120 switch (length) {
121 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
122 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
123 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
124 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
125 case 8 : b+=k[1]; a+=k[0]; break;
126 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
127 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
128 case 5 : b+=k[1]&0xff; a+=k[0]; break;
129 case 4 : a+=k[0]; break;
130 case 3 : a+=k[0]&0xffffff; break;
131 case 2 : a+=k[0]&0xffff; break;
132 case 1 : a+=k[0]&0xff; break;
133 case 0 : return c; /* zero length strings require no mixing */
134 }
135
136 #else /* make valgrind happy */
137 {
138 const uint8_t *k8;
139
140 k8 = (const uint8_t *) k;
141 switch (length) {
142 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
143 case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
144 case 10: c+=((uint32_t) k8[9])<<8; /* fall through */
145 case 9 : c+=k8[8]; /* fall through */
146 case 8 : b+=k[1]; a+=k[0]; break;
147 case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
148 case 6 : b+=((uint32_t) k8[5])<<8; /* fall through */
149 case 5 : b+=k8[4]; /* fall through */
150 case 4 : a+=k[0]; break;
151 case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
152 case 2 : a+=((uint32_t) k8[1])<<8; /* fall through */
153 case 1 : a+=k8[0]; break;
154 case 0 : return c;
155 }
156 }
157 #endif /* !valgrind */
158
159 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
160 const uint16_t *k = (const uint16_t *) key; /* read 16-bit chunks */
161 const uint8_t *k8;
162
163 /*--------------- all but last block: aligned reads and different mixing */
164 while (length > 12)
165 {
166 a += k[0] + (((uint32_t) k[1])<<16);
167 b += k[2] + (((uint32_t) k[3])<<16);
168 c += k[4] + (((uint32_t) k[5])<<16);
169 mix(a, b, c);
170 length -= 12;
171 k += 6;
172 }
173
174 /*----------------------------- handle the last (probably partial) block */
175 k8 = (const uint8_t *) k;
176 switch(length)
177 {
178 case 12: c+=k[4]+(((uint32_t) k[5])<<16);
179 b+=k[2]+(((uint32_t) k[3])<<16);
180 a+=k[0]+(((uint32_t) k[1])<<16);
181 break;
182 case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
183 case 10: c+=k[4];
184 b+=k[2]+(((uint32_t) k[3])<<16);
185 a+=k[0]+(((uint32_t) k[1])<<16);
186 break;
187 case 9 : c+=k8[8]; /* fall through */
188 case 8 : b+=k[2]+(((uint32_t) k[3])<<16);
189 a+=k[0]+(((uint32_t) k[1])<<16);
190 break;
191 case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
192 case 6 : b+=k[2];
193 a+=k[0]+(((uint32_t) k[1])<<16);
194 break;
195 case 5 : b+=k8[4]; /* fall through */
196 case 4 : a+=k[0]+(((uint32_t) k[1])<<16);
197 break;
198 case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
199 case 2 : a+=k[0];
200 break;
201 case 1 : a+=k8[0];
202 break;
203 case 0 : return c; /* zero length requires no mixing */
204 }
205
206 } else { /* need to read the key one byte at a time */
207 const uint8_t *k = (const uint8_t *)key;
208
209 /*--------------- all but the last block: affect some 32 bits of (a, b, c) */
210 while (length > 12) {
211 a += k[0];
212 a += ((uint32_t) k[1])<<8;
213 a += ((uint32_t) k[2])<<16;
214 a += ((uint32_t) k[3])<<24;
215 b += k[4];
216 b += ((uint32_t) k[5])<<8;
217 b += ((uint32_t) k[6])<<16;
218 b += ((uint32_t) k[7])<<24;
219 c += k[8];
220 c += ((uint32_t) k[9])<<8;
221 c += ((uint32_t) k[10])<<16;
222 c += ((uint32_t) k[11])<<24;
223 mix(a,b,c);
224 length -= 12;
225 k += 12;
226 }
227
228 /*-------------------------------- last block: affect all 32 bits of (c) */
229 switch (length) { /* all the case statements fall through */
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 }
245 }
246
247 final(a, b, c);
248 return c;
249 }
250
251 static inline
252 uint32_t jhash(const void *key, size_t length, uint32_t seed)
253 {
254 return hashlittle(key, length, seed);
255 }
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