Mercurial > embed
comparison jansson/src/lookup3.h @ 0:0047655db1aa
jansson: import 2.7
author | David Demelier <markand@malikania.fr> |
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date | Wed, 24 Feb 2016 20:50:05 +0100 |
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1 /* | |
2 ------------------------------------------------------------------------------- | |
3 lookup3.c, by Bob Jenkins, May 2006, Public Domain. | |
4 | |
5 These are functions for producing 32-bit hashes for hash table lookup. | |
6 hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() | |
7 are externally useful functions. Routines to test the hash are included | |
8 if SELF_TEST is defined. You can use this free for any purpose. It's in | |
9 the public domain. It has no warranty. | |
10 | |
11 You probably want to use hashlittle(). hashlittle() and hashbig() | |
12 hash byte arrays. hashlittle() is is faster than hashbig() on | |
13 little-endian machines. Intel and AMD are little-endian machines. | |
14 On second thought, you probably want hashlittle2(), which is identical to | |
15 hashlittle() except it returns two 32-bit hashes for the price of one. | |
16 You could implement hashbig2() if you wanted but I haven't bothered here. | |
17 | |
18 If you want to find a hash of, say, exactly 7 integers, do | |
19 a = i1; b = i2; c = i3; | |
20 mix(a,b,c); | |
21 a += i4; b += i5; c += i6; | |
22 mix(a,b,c); | |
23 a += i7; | |
24 final(a,b,c); | |
25 then use c as the hash value. If you have a variable length array of | |
26 4-byte integers to hash, use hashword(). If you have a byte array (like | |
27 a character string), use hashlittle(). If you have several byte arrays, or | |
28 a mix of things, see the comments above hashlittle(). | |
29 | |
30 Why is this so big? I read 12 bytes at a time into 3 4-byte integers, | |
31 then mix those integers. This is fast (you can do a lot more thorough | |
32 mixing with 12*3 instructions on 3 integers than you can with 3 instructions | |
33 on 1 byte), but shoehorning those bytes into integers efficiently is messy. | |
34 ------------------------------------------------------------------------------- | |
35 */ | |
36 | |
37 #include <stdlib.h> | |
38 | |
39 #ifdef HAVE_CONFIG_H | |
40 #include <jansson_private_config.h> | |
41 #endif | |
42 | |
43 #ifdef HAVE_STDINT_H | |
44 #include <stdint.h> /* defines uint32_t etc */ | |
45 #endif | |
46 | |
47 #ifdef HAVE_SYS_PARAM_H | |
48 #include <sys/param.h> /* attempt to define endianness */ | |
49 #endif | |
50 | |
51 #ifdef HAVE_ENDIAN_H | |
52 # include <endian.h> /* attempt to define endianness */ | |
53 #endif | |
54 | |
55 /* | |
56 * My best guess at if you are big-endian or little-endian. This may | |
57 * need adjustment. | |
58 */ | |
59 #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \ | |
60 __BYTE_ORDER == __LITTLE_ENDIAN) || \ | |
61 (defined(i386) || defined(__i386__) || defined(__i486__) || \ | |
62 defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL)) | |
63 # define HASH_LITTLE_ENDIAN 1 | |
64 # define HASH_BIG_ENDIAN 0 | |
65 #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \ | |
66 __BYTE_ORDER == __BIG_ENDIAN) || \ | |
67 (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel)) | |
68 # define HASH_LITTLE_ENDIAN 0 | |
69 # define HASH_BIG_ENDIAN 1 | |
70 #else | |
71 # define HASH_LITTLE_ENDIAN 0 | |
72 # define HASH_BIG_ENDIAN 0 | |
73 #endif | |
74 | |
75 #define hashsize(n) ((uint32_t)1<<(n)) | |
76 #define hashmask(n) (hashsize(n)-1) | |
77 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k)))) | |
78 | |
79 /* | |
80 ------------------------------------------------------------------------------- | |
81 mix -- mix 3 32-bit values reversibly. | |
82 | |
83 This is reversible, so any information in (a,b,c) before mix() is | |
84 still in (a,b,c) after mix(). | |
85 | |
86 If four pairs of (a,b,c) inputs are run through mix(), or through | |
87 mix() in reverse, there are at least 32 bits of the output that | |
88 are sometimes the same for one pair and different for another pair. | |
89 This was tested for: | |
90 * pairs that differed by one bit, by two bits, in any combination | |
91 of top bits of (a,b,c), or in any combination of bottom bits of | |
92 (a,b,c). | |
93 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed | |
94 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as | |
95 is commonly produced by subtraction) look like a single 1-bit | |
96 difference. | |
97 * the base values were pseudorandom, all zero but one bit set, or | |
98 all zero plus a counter that starts at zero. | |
99 | |
100 Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that | |
101 satisfy this are | |
102 4 6 8 16 19 4 | |
103 9 15 3 18 27 15 | |
104 14 9 3 7 17 3 | |
105 Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing | |
106 for "differ" defined as + with a one-bit base and a two-bit delta. I | |
107 used http://burtleburtle.net/bob/hash/avalanche.html to choose | |
108 the operations, constants, and arrangements of the variables. | |
109 | |
110 This does not achieve avalanche. There are input bits of (a,b,c) | |
111 that fail to affect some output bits of (a,b,c), especially of a. The | |
112 most thoroughly mixed value is c, but it doesn't really even achieve | |
113 avalanche in c. | |
114 | |
115 This allows some parallelism. Read-after-writes are good at doubling | |
116 the number of bits affected, so the goal of mixing pulls in the opposite | |
117 direction as the goal of parallelism. I did what I could. Rotates | |
118 seem to cost as much as shifts on every machine I could lay my hands | |
119 on, and rotates are much kinder to the top and bottom bits, so I used | |
120 rotates. | |
121 ------------------------------------------------------------------------------- | |
122 */ | |
123 #define mix(a,b,c) \ | |
124 { \ | |
125 a -= c; a ^= rot(c, 4); c += b; \ | |
126 b -= a; b ^= rot(a, 6); a += c; \ | |
127 c -= b; c ^= rot(b, 8); b += a; \ | |
128 a -= c; a ^= rot(c,16); c += b; \ | |
129 b -= a; b ^= rot(a,19); a += c; \ | |
130 c -= b; c ^= rot(b, 4); b += a; \ | |
131 } | |
132 | |
133 /* | |
134 ------------------------------------------------------------------------------- | |
135 final -- final mixing of 3 32-bit values (a,b,c) into c | |
136 | |
137 Pairs of (a,b,c) values differing in only a few bits will usually | |
138 produce values of c that look totally different. This was tested for | |
139 * pairs that differed by one bit, by two bits, in any combination | |
140 of top bits of (a,b,c), or in any combination of bottom bits of | |
141 (a,b,c). | |
142 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed | |
143 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as | |
144 is commonly produced by subtraction) look like a single 1-bit | |
145 difference. | |
146 * the base values were pseudorandom, all zero but one bit set, or | |
147 all zero plus a counter that starts at zero. | |
148 | |
149 These constants passed: | |
150 14 11 25 16 4 14 24 | |
151 12 14 25 16 4 14 24 | |
152 and these came close: | |
153 4 8 15 26 3 22 24 | |
154 10 8 15 26 3 22 24 | |
155 11 8 15 26 3 22 24 | |
156 ------------------------------------------------------------------------------- | |
157 */ | |
158 #define final(a,b,c) \ | |
159 { \ | |
160 c ^= b; c -= rot(b,14); \ | |
161 a ^= c; a -= rot(c,11); \ | |
162 b ^= a; b -= rot(a,25); \ | |
163 c ^= b; c -= rot(b,16); \ | |
164 a ^= c; a -= rot(c,4); \ | |
165 b ^= a; b -= rot(a,14); \ | |
166 c ^= b; c -= rot(b,24); \ | |
167 } | |
168 | |
169 /* | |
170 ------------------------------------------------------------------------------- | |
171 hashlittle() -- hash a variable-length key into a 32-bit value | |
172 k : the key (the unaligned variable-length array of bytes) | |
173 length : the length of the key, counting by bytes | |
174 initval : can be any 4-byte value | |
175 Returns a 32-bit value. Every bit of the key affects every bit of | |
176 the return value. Two keys differing by one or two bits will have | |
177 totally different hash values. | |
178 | |
179 The best hash table sizes are powers of 2. There is no need to do | |
180 mod a prime (mod is sooo slow!). If you need less than 32 bits, | |
181 use a bitmask. For example, if you need only 10 bits, do | |
182 h = (h & hashmask(10)); | |
183 In which case, the hash table should have hashsize(10) elements. | |
184 | |
185 If you are hashing n strings (uint8_t **)k, do it like this: | |
186 for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h); | |
187 | |
188 By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this | |
189 code any way you wish, private, educational, or commercial. It's free. | |
190 | |
191 Use for hash table lookup, or anything where one collision in 2^^32 is | |
192 acceptable. Do NOT use for cryptographic purposes. | |
193 ------------------------------------------------------------------------------- | |
194 */ | |
195 | |
196 static uint32_t hashlittle(const void *key, size_t length, uint32_t initval) | |
197 { | |
198 uint32_t a,b,c; /* internal state */ | |
199 union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */ | |
200 | |
201 /* Set up the internal state */ | |
202 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval; | |
203 | |
204 u.ptr = key; | |
205 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) { | |
206 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */ | |
207 | |
208 /* Detect Valgrind or AddressSanitizer */ | |
209 #ifdef VALGRIND | |
210 # define NO_MASKING_TRICK 1 | |
211 #else | |
212 # if defined(__has_feature) /* Clang */ | |
213 # if __has_feature(address_sanitizer) /* is ASAN enabled? */ | |
214 # define NO_MASKING_TRICK 1 | |
215 # endif | |
216 # else | |
217 # if defined(__SANITIZE_ADDRESS__) /* GCC 4.8.x, is ASAN enabled? */ | |
218 # define NO_MASKING_TRICK 1 | |
219 # endif | |
220 # endif | |
221 #endif | |
222 | |
223 #ifdef NO_MASKING_TRICK | |
224 const uint8_t *k8; | |
225 #endif | |
226 | |
227 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */ | |
228 while (length > 12) | |
229 { | |
230 a += k[0]; | |
231 b += k[1]; | |
232 c += k[2]; | |
233 mix(a,b,c); | |
234 length -= 12; | |
235 k += 3; | |
236 } | |
237 | |
238 /*----------------------------- handle the last (probably partial) block */ | |
239 /* | |
240 * "k[2]&0xffffff" actually reads beyond the end of the string, but | |
241 * then masks off the part it's not allowed to read. Because the | |
242 * string is aligned, the masked-off tail is in the same word as the | |
243 * rest of the string. Every machine with memory protection I've seen | |
244 * does it on word boundaries, so is OK with this. But VALGRIND will | |
245 * still catch it and complain. The masking trick does make the hash | |
246 * noticably faster for short strings (like English words). | |
247 */ | |
248 #ifndef NO_MASKING_TRICK | |
249 | |
250 switch(length) | |
251 { | |
252 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; | |
253 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break; | |
254 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break; | |
255 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break; | |
256 case 8 : b+=k[1]; a+=k[0]; break; | |
257 case 7 : b+=k[1]&0xffffff; a+=k[0]; break; | |
258 case 6 : b+=k[1]&0xffff; a+=k[0]; break; | |
259 case 5 : b+=k[1]&0xff; a+=k[0]; break; | |
260 case 4 : a+=k[0]; break; | |
261 case 3 : a+=k[0]&0xffffff; break; | |
262 case 2 : a+=k[0]&0xffff; break; | |
263 case 1 : a+=k[0]&0xff; break; | |
264 case 0 : return c; /* zero length strings require no mixing */ | |
265 } | |
266 | |
267 #else /* make valgrind happy */ | |
268 | |
269 k8 = (const uint8_t *)k; | |
270 switch(length) | |
271 { | |
272 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break; | |
273 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ | |
274 case 10: c+=((uint32_t)k8[9])<<8; /* fall through */ | |
275 case 9 : c+=k8[8]; /* fall through */ | |
276 case 8 : b+=k[1]; a+=k[0]; break; | |
277 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ | |
278 case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */ | |
279 case 5 : b+=k8[4]; /* fall through */ | |
280 case 4 : a+=k[0]; break; | |
281 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ | |
282 case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */ | |
283 case 1 : a+=k8[0]; break; | |
284 case 0 : return c; | |
285 } | |
286 | |
287 #endif /* !valgrind */ | |
288 | |
289 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) { | |
290 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */ | |
291 const uint8_t *k8; | |
292 | |
293 /*--------------- all but last block: aligned reads and different mixing */ | |
294 while (length > 12) | |
295 { | |
296 a += k[0] + (((uint32_t)k[1])<<16); | |
297 b += k[2] + (((uint32_t)k[3])<<16); | |
298 c += k[4] + (((uint32_t)k[5])<<16); | |
299 mix(a,b,c); | |
300 length -= 12; | |
301 k += 6; | |
302 } | |
303 | |
304 /*----------------------------- handle the last (probably partial) block */ | |
305 k8 = (const uint8_t *)k; | |
306 switch(length) | |
307 { | |
308 case 12: c+=k[4]+(((uint32_t)k[5])<<16); | |
309 b+=k[2]+(((uint32_t)k[3])<<16); | |
310 a+=k[0]+(((uint32_t)k[1])<<16); | |
311 break; | |
312 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */ | |
313 case 10: c+=k[4]; | |
314 b+=k[2]+(((uint32_t)k[3])<<16); | |
315 a+=k[0]+(((uint32_t)k[1])<<16); | |
316 break; | |
317 case 9 : c+=k8[8]; /* fall through */ | |
318 case 8 : b+=k[2]+(((uint32_t)k[3])<<16); | |
319 a+=k[0]+(((uint32_t)k[1])<<16); | |
320 break; | |
321 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */ | |
322 case 6 : b+=k[2]; | |
323 a+=k[0]+(((uint32_t)k[1])<<16); | |
324 break; | |
325 case 5 : b+=k8[4]; /* fall through */ | |
326 case 4 : a+=k[0]+(((uint32_t)k[1])<<16); | |
327 break; | |
328 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */ | |
329 case 2 : a+=k[0]; | |
330 break; | |
331 case 1 : a+=k8[0]; | |
332 break; | |
333 case 0 : return c; /* zero length requires no mixing */ | |
334 } | |
335 | |
336 } else { /* need to read the key one byte at a time */ | |
337 const uint8_t *k = (const uint8_t *)key; | |
338 | |
339 /*--------------- all but the last block: affect some 32 bits of (a,b,c) */ | |
340 while (length > 12) | |
341 { | |
342 a += k[0]; | |
343 a += ((uint32_t)k[1])<<8; | |
344 a += ((uint32_t)k[2])<<16; | |
345 a += ((uint32_t)k[3])<<24; | |
346 b += k[4]; | |
347 b += ((uint32_t)k[5])<<8; | |
348 b += ((uint32_t)k[6])<<16; | |
349 b += ((uint32_t)k[7])<<24; | |
350 c += k[8]; | |
351 c += ((uint32_t)k[9])<<8; | |
352 c += ((uint32_t)k[10])<<16; | |
353 c += ((uint32_t)k[11])<<24; | |
354 mix(a,b,c); | |
355 length -= 12; | |
356 k += 12; | |
357 } | |
358 | |
359 /*-------------------------------- last block: affect all 32 bits of (c) */ | |
360 switch(length) /* all the case statements fall through */ | |
361 { | |
362 case 12: c+=((uint32_t)k[11])<<24; | |
363 case 11: c+=((uint32_t)k[10])<<16; | |
364 case 10: c+=((uint32_t)k[9])<<8; | |
365 case 9 : c+=k[8]; | |
366 case 8 : b+=((uint32_t)k[7])<<24; | |
367 case 7 : b+=((uint32_t)k[6])<<16; | |
368 case 6 : b+=((uint32_t)k[5])<<8; | |
369 case 5 : b+=k[4]; | |
370 case 4 : a+=((uint32_t)k[3])<<24; | |
371 case 3 : a+=((uint32_t)k[2])<<16; | |
372 case 2 : a+=((uint32_t)k[1])<<8; | |
373 case 1 : a+=k[0]; | |
374 break; | |
375 case 0 : return c; | |
376 } | |
377 } | |
378 | |
379 final(a,b,c); | |
380 return c; | |
381 } |