cleanup: spelling fixes in comments
[urcu.git] / doc / examples / rculfhash / jhash.h
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1#ifndef _JHASH_H
2#define _JHASH_H
3
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4#if defined(__FreeBSD__)
5#include <sys/endian.h>
6#endif
7
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8/*
9 * jhash.h
10 *
11 * Example hash function.
12 *
13 * Copyright 2009-2012 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
14 *
15 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
16 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
17 *
18 * Permission is hereby granted to use or copy this program for any
19 * purpose, provided the above notices are retained on all copies.
20 * Permission to modify the code and to distribute modified code is
21 * granted, provided the above notices are retained, and a notice that
22 * the code was modified is included with the above copyright notice.
23 */
24
25/*
26 * Hash function
27 * Source: http://burtleburtle.net/bob/c/lookup3.c
28 * Originally Public Domain
29 */
30
31#define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
32
33#define mix(a, b, c) \
34do { \
35 a -= c; a ^= rot(c, 4); c += b; \
36 b -= a; b ^= rot(a, 6); a += c; \
37 c -= b; c ^= rot(b, 8); b += a; \
38 a -= c; a ^= rot(c, 16); c += b; \
39 b -= a; b ^= rot(a, 19); a += c; \
40 c -= b; c ^= rot(b, 4); b += a; \
41} while (0)
42
43#define final(a, b, c) \
44{ \
45 c ^= b; c -= rot(b, 14); \
46 a ^= c; a -= rot(c, 11); \
47 b ^= a; b -= rot(a, 25); \
48 c ^= b; c -= rot(b, 16); \
49 a ^= c; a -= rot(c, 4); \
50 b ^= a; b -= rot(a, 14); \
51 c ^= b; c -= rot(b, 24); \
52}
53
54#if (BYTE_ORDER == LITTLE_ENDIAN)
55#define HASH_LITTLE_ENDIAN 1
56#else
57#define HASH_LITTLE_ENDIAN 0
58#endif
59
60/*
61 *
62 * hashlittle() -- hash a variable-length key into a 32-bit value
63 * k : the key (the unaligned variable-length array of bytes)
64 * length : the length of the key, counting by bytes
65 * initval : can be any 4-byte value
66 * Returns a 32-bit value. Every bit of the key affects every bit of
67 * the return value. Two keys differing by one or two bits will have
68 * totally different hash values.
69 *
70 * The best hash table sizes are powers of 2. There is no need to do
71 * mod a prime (mod is sooo slow!). If you need less than 32 bits,
72 * use a bitmask. For example, if you need only 10 bits, do
73 * h = (h & hashmask(10));
74 * In which case, the hash table should have hashsize(10) elements.
75 *
76 * If you are hashing n strings (uint8_t **)k, do it like this:
77 * for (i = 0, h = 0; i < n; ++i) h = hashlittle(k[i], len[i], h);
78 *
79 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
80 * code any way you wish, private, educational, or commercial. It's free.
81 *
82 * Use for hash table lookup, or anything where one collision in 2^^32 is
83 * acceptable. Do NOT use for cryptographic purposes.
84 */
85static
86uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
87{
88 uint32_t a, b, c; /* internal state */
89 union {
90 const void *ptr;
91 size_t i;
92 } u;
93
94 /* Set up the internal state */
95 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
96
97 u.ptr = key;
98 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
99 const uint32_t *k = (const uint32_t *) key; /* read 32-bit chunks */
100
101 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
102 while (length > 12) {
103 a += k[0];
104 b += k[1];
105 c += k[2];
106 mix(a, b, c);
107 length -= 12;
108 k += 3;
109 }
110
111 /*----------------------------- handle the last (probably partial) block */
112 /*
113 * "k[2]&0xffffff" actually reads beyond the end of the string, but
114 * then masks off the part it's not allowed to read. Because the
115 * string is aligned, the masked-off tail is in the same word as the
116 * rest of the string. Every machine with memory protection I've seen
117 * does it on word boundaries, so is OK with this. But VALGRIND will
118 * still catch it and complain. The masking trick does make the hash
f99c6e92 119 * noticeably faster for short strings (like English words).
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120 */
121#ifndef VALGRIND
122
123 switch (length) {
124 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
125 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
126 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
127 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
128 case 8 : b+=k[1]; a+=k[0]; break;
129 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
130 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
131 case 5 : b+=k[1]&0xff; a+=k[0]; break;
132 case 4 : a+=k[0]; break;
133 case 3 : a+=k[0]&0xffffff; break;
134 case 2 : a+=k[0]&0xffff; break;
135 case 1 : a+=k[0]&0xff; break;
136 case 0 : return c; /* zero length strings require no mixing */
137 }
138
139#else /* make valgrind happy */
140 {
141 const uint8_t *k8;
142
143 k8 = (const uint8_t *) k;
144 switch (length) {
145 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
146 case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
147 case 10: c+=((uint32_t) k8[9])<<8; /* fall through */
148 case 9 : c+=k8[8]; /* fall through */
149 case 8 : b+=k[1]; a+=k[0]; break;
150 case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
151 case 6 : b+=((uint32_t) k8[5])<<8; /* fall through */
152 case 5 : b+=k8[4]; /* fall through */
153 case 4 : a+=k[0]; break;
154 case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
155 case 2 : a+=((uint32_t) k8[1])<<8; /* fall through */
156 case 1 : a+=k8[0]; break;
157 case 0 : return c;
158 }
159 }
160#endif /* !valgrind */
161
162 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
163 const uint16_t *k = (const uint16_t *) key; /* read 16-bit chunks */
164 const uint8_t *k8;
165
166 /*--------------- all but last block: aligned reads and different mixing */
167 while (length > 12)
168 {
169 a += k[0] + (((uint32_t) k[1])<<16);
170 b += k[2] + (((uint32_t) k[3])<<16);
171 c += k[4] + (((uint32_t) k[5])<<16);
172 mix(a, b, c);
173 length -= 12;
174 k += 6;
175 }
176
177 /*----------------------------- handle the last (probably partial) block */
178 k8 = (const uint8_t *) k;
179 switch(length)
180 {
181 case 12: c+=k[4]+(((uint32_t) k[5])<<16);
182 b+=k[2]+(((uint32_t) k[3])<<16);
183 a+=k[0]+(((uint32_t) k[1])<<16);
184 break;
185 case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
186 case 10: c+=k[4];
187 b+=k[2]+(((uint32_t) k[3])<<16);
188 a+=k[0]+(((uint32_t) k[1])<<16);
189 break;
190 case 9 : c+=k8[8]; /* fall through */
191 case 8 : b+=k[2]+(((uint32_t) k[3])<<16);
192 a+=k[0]+(((uint32_t) k[1])<<16);
193 break;
194 case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
195 case 6 : b+=k[2];
196 a+=k[0]+(((uint32_t) k[1])<<16);
197 break;
198 case 5 : b+=k8[4]; /* fall through */
199 case 4 : a+=k[0]+(((uint32_t) k[1])<<16);
200 break;
201 case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
202 case 2 : a+=k[0];
203 break;
204 case 1 : a+=k8[0];
205 break;
206 case 0 : return c; /* zero length requires no mixing */
207 }
208
209 } else { /* need to read the key one byte at a time */
210 const uint8_t *k = (const uint8_t *)key;
211
212 /*--------------- all but the last block: affect some 32 bits of (a, b, c) */
213 while (length > 12) {
214 a += k[0];
215 a += ((uint32_t) k[1])<<8;
216 a += ((uint32_t) k[2])<<16;
217 a += ((uint32_t) k[3])<<24;
218 b += k[4];
219 b += ((uint32_t) k[5])<<8;
220 b += ((uint32_t) k[6])<<16;
221 b += ((uint32_t) k[7])<<24;
222 c += k[8];
223 c += ((uint32_t) k[9])<<8;
224 c += ((uint32_t) k[10])<<16;
225 c += ((uint32_t) k[11])<<24;
226 mix(a,b,c);
227 length -= 12;
228 k += 12;
229 }
230
231 /*-------------------------------- last block: affect all 32 bits of (c) */
232 switch (length) { /* all the case statements fall through */
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233 case 12: c+=((uint32_t) k[11])<<24; /* fall through */
234 case 11: c+=((uint32_t) k[10])<<16; /* fall through */
235 case 10: c+=((uint32_t) k[9])<<8; /* fall through */
236 case 9 : c+=k[8]; /* fall through */
237 case 8 : b+=((uint32_t) k[7])<<24; /* fall through */
238 case 7 : b+=((uint32_t) k[6])<<16; /* fall through */
239 case 6 : b+=((uint32_t) k[5])<<8; /* fall through */
240 case 5 : b+=k[4]; /* fall through */
241 case 4 : a+=((uint32_t) k[3])<<24; /* fall through */
242 case 3 : a+=((uint32_t) k[2])<<16; /* fall through */
243 case 2 : a+=((uint32_t) k[1])<<8; /* fall through */
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244 case 1 : a+=k[0];
245 break;
246 case 0 : return c;
247 }
248 }
249
250 final(a, b, c);
251 return c;
252}
253
254static inline
255uint32_t jhash(const void *key, size_t length, uint32_t seed)
256{
257 return hashlittle(key, length, seed);
258}
259
260#endif /* _JHASH_H */
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