Fix warning about hash type
[lttng-tools.git] / hashtable / hash.c
1 /*
2 * Copyright (C) - Bob Jenkins, May 2006, Public Domain.
3 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
4 * Copyright (C) 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 *
6 * These are functions for producing 32-bit hashes for hash table lookup.
7 * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() are
8 * externally useful functions. Routines to test the hash are included if
9 * SELF_TEST is defined. You can use this free for any purpose. It's in the
10 * public domain. It has no warranty.
11 *
12 * You probably want to use hashlittle(). hashlittle() and hashbig() hash byte
13 * arrays. hashlittle() is is faster than hashbig() on little-endian machines.
14 * Intel and AMD are little-endian machines. On second thought, you probably
15 * want hashlittle2(), which is identical to hashlittle() except it returns two
16 * 32-bit hashes for the price of one. You could implement hashbig2() if you
17 * wanted but I haven't bothered here.
18 *
19 * If you want to find a hash of, say, exactly 7 integers, do
20 * a = i1; b = i2; c = i3;
21 * mix(a,b,c);
22 * a += i4; b += i5; c += i6;
23 * mix(a,b,c);
24 * a += i7;
25 * final(a,b,c);
26 * then use c as the hash value. If you have a variable length array of
27 * 4-byte integers to hash, use hashword(). If you have a byte array (like
28 * a character string), use hashlittle(). If you have several byte arrays, or
29 * a mix of things, see the comments above hashlittle().
30 *
31 * Why is this so big? I read 12 bytes at a time into 3 4-byte integers, then
32 * mix those integers. This is fast (you can do a lot more thorough mixing
33 * with 12*3 instructions on 3 integers than you can with 3 instructions on 1
34 * byte), but shoehorning those bytes into integers efficiently is messy.
35 */
36
37 #include <stdio.h> /* defines printf for tests */
38 #include <time.h> /* defines time_t for timings in the test */
39 #include <stdint.h> /* defines uint32_t etc */
40 #include <sys/param.h> /* attempt to define endianness */
41 #include <endian.h> /* attempt to define endianness */
42 #include <string.h>
43 #include <assert.h>
44 #include <urcu/compiler.h>
45
46 /*
47 * My best guess at if you are big-endian or little-endian. This may
48 * need adjustment.
49 */
50 #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \
51 __BYTE_ORDER == __LITTLE_ENDIAN) || \
52 (defined(i386) || defined(__i386__) || defined(__i486__) || \
53 defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL))
54 # define HASH_LITTLE_ENDIAN 1
55 # define HASH_BIG_ENDIAN 0
56 #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \
57 __BYTE_ORDER == __BIG_ENDIAN) || \
58 (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel))
59 # define HASH_LITTLE_ENDIAN 0
60 # define HASH_BIG_ENDIAN 1
61 #else
62 # define HASH_LITTLE_ENDIAN 0
63 # define HASH_BIG_ENDIAN 0
64 #endif
65
66 #define hashsize(n) ((uint32_t)1<<(n))
67 #define hashmask(n) (hashsize(n)-1)
68 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
69
70 /*
71 * mix -- mix 3 32-bit values reversibly.
72 *
73 * This is reversible, so any information in (a,b,c) before mix() is
74 * still in (a,b,c) after mix().
75 *
76 * If four pairs of (a,b,c) inputs are run through mix(), or through
77 * mix() in reverse, there are at least 32 bits of the output that
78 * are sometimes the same for one pair and different for another pair.
79 * This was tested for:
80 * * pairs that differed by one bit, by two bits, in any combination
81 * of top bits of (a,b,c), or in any combination of bottom bits of
82 * (a,b,c).
83 * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
84 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
85 * is commonly produced by subtraction) look like a single 1-bit
86 * difference.
87 * * the base values were pseudorandom, all zero but one bit set, or
88 * all zero plus a counter that starts at zero.
89 *
90 * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
91 * satisfy this are
92 * 4 6 8 16 19 4
93 * 9 15 3 18 27 15
94 * 14 9 3 7 17 3
95 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
96 * for "differ" defined as + with a one-bit base and a two-bit delta. I
97 * used http://burtleburtle.net/bob/hash/avalanche.html to choose
98 * the operations, constants, and arrangements of the variables.
99 *
100 * This does not achieve avalanche. There are input bits of (a,b,c)
101 * that fail to affect some output bits of (a,b,c), especially of a. The
102 * most thoroughly mixed value is c, but it doesn't really even achieve
103 * avalanche in c.
104 *
105 * This allows some parallelism. Read-after-writes are good at doubling
106 * the number of bits affected, so the goal of mixing pulls in the opposite
107 * direction as the goal of parallelism. I did what I could. Rotates
108 * seem to cost as much as shifts on every machine I could lay my hands
109 * on, and rotates are much kinder to the top and bottom bits, so I used
110 * rotates.
111 */
112 #define mix(a,b,c) \
113 { \
114 a -= c; a ^= rot(c, 4); c += b; \
115 b -= a; b ^= rot(a, 6); a += c; \
116 c -= b; c ^= rot(b, 8); b += a; \
117 a -= c; a ^= rot(c,16); c += b; \
118 b -= a; b ^= rot(a,19); a += c; \
119 c -= b; c ^= rot(b, 4); b += a; \
120 }
121
122 /*
123 * final -- final mixing of 3 32-bit values (a,b,c) into c
124 *
125 * Pairs of (a,b,c) values differing in only a few bits will usually
126 * produce values of c that look totally different. This was tested for
127 * * pairs that differed by one bit, by two bits, in any combination
128 * of top bits of (a,b,c), or in any combination of bottom bits of
129 * (a,b,c).
130 * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
131 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
132 * is commonly produced by subtraction) look like a single 1-bit
133 * difference.
134 * * the base values were pseudorandom, all zero but one bit set, or
135 * all zero plus a counter that starts at zero.
136 *
137 * These constants passed:
138 * 14 11 25 16 4 14 24
139 * 12 14 25 16 4 14 24
140 * and these came close:
141 * 4 8 15 26 3 22 24
142 * 10 8 15 26 3 22 24
143 * 11 8 15 26 3 22 24
144 */
145 #define final(a,b,c) \
146 { \
147 c ^= b; c -= rot(b,14); \
148 a ^= c; a -= rot(c,11); \
149 b ^= a; b -= rot(a,25); \
150 c ^= b; c -= rot(b,16); \
151 a ^= c; a -= rot(c,4); \
152 b ^= a; b -= rot(a,14); \
153 c ^= b; c -= rot(b,24); \
154 }
155
156 static __attribute__((unused))
157 uint32_t hashword(
158 const uint32_t *k, /* the key, an array of uint32_t values */
159 size_t length, /* the length of the key, in uint32_ts */
160 uint32_t initval) /* the previous hash, or an arbitrary value */
161 {
162 uint32_t a, b, c;
163
164 /* Set up the internal state */
165 a = b = c = 0xdeadbeef + (((uint32_t) length) << 2) + initval;
166
167 /*----------------------------------------- handle most of the key */
168 while (length > 3) {
169 a += k[0];
170 b += k[1];
171 c += k[2];
172 mix(a, b, c);
173 length -= 3;
174 k += 3;
175 }
176
177 /*----------------------------------- handle the last 3 uint32_t's */
178 switch (length) { /* all the case statements fall through */
179 case 3: c += k[2];
180 case 2: b += k[1];
181 case 1: a += k[0];
182 final(a, b, c);
183 case 0: /* case 0: nothing left to add */
184 break;
185 }
186 /*---------------------------------------------- report the result */
187 return c;
188 }
189
190
191 /*
192 * hashword2() -- same as hashword(), but take two seeds and return two 32-bit
193 * values. pc and pb must both be nonnull, and *pc and *pb must both be
194 * initialized with seeds. If you pass in (*pb)==0, the output (*pc) will be
195 * the same as the return value from hashword().
196 */
197 static __attribute__((unused))
198 void hashword2(const uint32_t *k, size_t length,
199 uint32_t *pc, uint32_t *pb)
200 {
201 uint32_t a, b, c;
202
203 /* Set up the internal state */
204 a = b = c = 0xdeadbeef + ((uint32_t) (length << 2)) + *pc;
205 c += *pb;
206
207 while (length > 3) {
208 a += k[0];
209 b += k[1];
210 c += k[2];
211 mix(a, b, c);
212 length -= 3;
213 k += 3;
214 }
215
216 switch (length) {
217 case 3 :
218 c += k[2];
219 case 2 :
220 b += k[1];
221 case 1 :
222 a += k[0];
223 final(a, b, c);
224 case 0: /* case 0: nothing left to add */
225 break;
226 }
227
228 *pc = c;
229 *pb = b;
230 }
231
232 /*
233 * hashlittle() -- hash a variable-length key into a 32-bit value
234 * k : the key (the unaligned variable-length array of bytes)
235 * length : the length of the key, counting by bytes
236 * initval : can be any 4-byte value
237 * Returns a 32-bit value. Every bit of the key affects every bit of
238 * the return value. Two keys differing by one or two bits will have
239 * totally different hash values.
240 *
241 * The best hash table sizes are powers of 2. There is no need to do
242 * mod a prime (mod is sooo slow!). If you need less than 32 bits,
243 * use a bitmask. For example, if you need only 10 bits, do
244 * h = (h & hashmask(10));
245 * In which case, the hash table should have hashsize(10) elements.
246 *
247 * If you are hashing n strings (uint8_t **)k, do it like this:
248 * for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
249 *
250 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
251 * code any way you wish, private, educational, or commercial. It's free.
252 *
253 * Use for hash table lookup, or anything where one collision in 2^^32 is
254 * acceptable. Do NOT use for cryptographic purposes.
255 */
256
257 static uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
258 {
259 uint32_t a,b,c;
260 union {
261 const void *ptr;
262 size_t i;
263 } u; /* needed for Mac Powerbook G4 */
264
265 /* Set up the internal state */
266 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
267
268 u.ptr = key;
269 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
270 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
271
272 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
273 while (length > 12) {
274 a += k[0];
275 b += k[1];
276 c += k[2];
277 mix(a,b,c);
278 length -= 12;
279 k += 3;
280 }
281
282 /*
283 * "k[2]&0xffffff" actually reads beyond the end of the string, but
284 * then masks off the part it's not allowed to read. Because the
285 * string is aligned, the masked-off tail is in the same word as the
286 * rest of the string. Every machine with memory protection I've seen
287 * does it on word boundaries, so is OK with this. But VALGRIND will
288 * still catch it and complain. The masking trick does make the hash
289 * noticably faster for short strings (like English words).
290 */
291 #ifndef VALGRIND
292
293 switch (length) {
294 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
295 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
296 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
297 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
298 case 8 : b+=k[1]; a+=k[0]; break;
299 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
300 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
301 case 5 : b+=k[1]&0xff; a+=k[0]; break;
302 case 4 : a+=k[0]; break;
303 case 3 : a+=k[0]&0xffffff; break;
304 case 2 : a+=k[0]&0xffff; break;
305 case 1 : a+=k[0]&0xff; break;
306 case 0 : return c; /* zero length strings require no mixing */
307 }
308 #else /* make valgrind happy */
309 const uint8_t *k8;
310
311 k8 = (const uint8_t *)k;
312 switch (length) {
313 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
314 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
315 case 10: c+=((uint32_t)k8[9])<<8; /* fall through */
316 case 9 : c+=k8[8]; /* fall through */
317 case 8 : b+=k[1]; a+=k[0]; break;
318 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
319 case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */
320 case 5 : b+=k8[4]; /* fall through */
321 case 4 : a+=k[0]; break;
322 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
323 case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */
324 case 1 : a+=k8[0]; break;
325 case 0 : return c;
326 }
327 #endif /* !valgrind */
328 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
329 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
330 const uint8_t *k8;
331
332 /*--------------- all but last block: aligned reads and different mixing */
333 while (length > 12) {
334 a += k[0] + (((uint32_t)k[1])<<16);
335 b += k[2] + (((uint32_t)k[3])<<16);
336 c += k[4] + (((uint32_t)k[5])<<16);
337 mix(a,b,c);
338 length -= 12;
339 k += 6;
340 }
341
342 k8 = (const uint8_t *)k;
343 switch (length) {
344 case 12:
345 c+=k[4]+(((uint32_t)k[5])<<16);
346 b+=k[2]+(((uint32_t)k[3])<<16);
347 a+=k[0]+(((uint32_t)k[1])<<16);
348 break;
349 case 11:
350 c+=((uint32_t)k8[10])<<16; /* fall through */
351 case 10:
352 c+=k[4];
353 b+=k[2]+(((uint32_t)k[3])<<16);
354 a+=k[0]+(((uint32_t)k[1])<<16);
355 break;
356 case 9:
357 c+=k8[8]; /* fall through */
358 case 8:
359 b+=k[2]+(((uint32_t)k[3])<<16);
360 a+=k[0]+(((uint32_t)k[1])<<16);
361 break;
362 case 7:
363 b+=((uint32_t)k8[6])<<16; /* fall through */
364 case 6:
365 b+=k[2];
366 a+=k[0]+(((uint32_t)k[1])<<16);
367 break;
368 case 5:
369 b+=k8[4]; /* fall through */
370 case 4:
371 a+=k[0]+(((uint32_t)k[1])<<16);
372 break;
373 case 3:
374 a+=((uint32_t)k8[2])<<16; /* fall through */
375 case 2:
376 a+=k[0];
377 break;
378 case 1:
379 a+=k8[0];
380 break;
381 case 0:
382 return c; /* zero length requires no mixing */
383 }
384
385 } else { /* need to read the key one byte at a time */
386 const uint8_t *k = (const uint8_t *)key;
387
388 while (length > 12) {
389 a += k[0];
390 a += ((uint32_t)k[1])<<8;
391 a += ((uint32_t)k[2])<<16;
392 a += ((uint32_t)k[3])<<24;
393 b += k[4];
394 b += ((uint32_t)k[5])<<8;
395 b += ((uint32_t)k[6])<<16;
396 b += ((uint32_t)k[7])<<24;
397 c += k[8];
398 c += ((uint32_t)k[9])<<8;
399 c += ((uint32_t)k[10])<<16;
400 c += ((uint32_t)k[11])<<24;
401 mix(a,b,c);
402 length -= 12;
403 k += 12;
404 }
405
406 switch(length) { /* all the case statements fall through */
407 case 12: c+=((uint32_t)k[11])<<24;
408 case 11: c+=((uint32_t)k[10])<<16;
409 case 10: c+=((uint32_t)k[9])<<8;
410 case 9: c+=k[8];
411 case 8: b+=((uint32_t)k[7])<<24;
412 case 7: b+=((uint32_t)k[6])<<16;
413 case 6: b+=((uint32_t)k[5])<<8;
414 case 5: b+=k[4];
415 case 4: a+=((uint32_t)k[3])<<24;
416 case 3: a+=((uint32_t)k[2])<<16;
417 case 2: a+=((uint32_t)k[1])<<8;
418 case 1:
419 a+=k[0];
420 break;
421 case 0:
422 return c;
423 }
424 }
425
426 final(a,b,c);
427 return c;
428 }
429
430 #if (CAA_BITS_PER_LONG == 64)
431 /*
432 * Hash function for number value.
433 */
434 unsigned long hash_key(void *_key, size_t length, unsigned long seed)
435 {
436 union {
437 uint64_t v64;
438 uint32_t v32[2];
439 } v;
440 union {
441 uint64_t v64;
442 uint32_t v32[2];
443 } key;
444
445 assert(length == sizeof(unsigned long));
446 v.v64 = (uint64_t) seed;
447 key.v64 = (uint64_t) _key;
448 hashword2(key.v32, 2, &v.v32[0], &v.v32[1]);
449 return v.v64;
450 }
451 #else
452 /*
453 * Hash function for number value.
454 */
455 unsigned long hash_key(void *_key, size_t length, unsigned long seed)
456 {
457 uint32_t key = (uint32_t) _key;
458
459 assert(length == sizeof(uint32_t));
460 return hashword(&key, 1, seed);
461 }
462 #endif
463
464 /*
465 * Hash function for string.
466 */
467 unsigned long hash_key_str(void *key, size_t length, unsigned long seed)
468 {
469 return hashlittle(key, length, seed);
470 }
471
472 /*
473 * Hash function compare for number value.
474 */
475 unsigned long hash_compare_key(void *key1, size_t key1_len,
476 void *key2, size_t key2_len)
477 {
478 if (key1_len != key2_len) {
479 return -1;
480 }
481
482 if (key1 == key2) {
483 return 0;
484 }
485
486 return 1;
487 }
488
489 /*
490 * Hash compare function for string.
491 */
492 unsigned long hash_compare_key_str(void *key1, size_t key1_len,
493 void *key2, size_t key2_len)
494 {
495 if (key1_len != key2_len) {
496 return -1;
497 }
498
499 if (strncmp(key1, key2, key1_len) == 0) {
500 return 0;
501 }
502
503 return 1;
504 }
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