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1 /***************************************************************************
2 * __________ __ ___.
3 * Open \______ \ ____ ____ | | _\_ |__ _______ ___
4 * Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
5 * Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
6 * Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
7 * \/ \/ \/ \/ \/
8 * $Id$
10 * Copyright (C) 2006 Bob Jenkins
11 * http://burtleburtle.net/bob/c/lookup3.c
13 * This program is free software; you can redistribute it and/or
14 * modify it under the terms of the GNU General Public License
15 * as published by the Free Software Foundation; either version 2
16 * of the License, or (at your option) any later version.
18 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
19 * KIND, either express or implied.
21 ****************************************************************************/
23 lookup3.c, by Bob Jenkins, May 2006, Public Domain.
25 These are functions for producing 32-bit hashes for hash table lookup.
26 hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
27 are externally useful functions. Routines to test the hash are included
28 if SELF_TEST is defined. You can use this free for any purpose. It's in
29 the public domain. It has no warranty.
31 You probably want to use hashlittle(). hashlittle() and hashbig()
32 hash byte arrays. hashlittle() is is faster than hashbig() on
33 little-endian machines. Intel and AMD are little-endian machines.
34 On second thought, you probably want hashlittle2(), which is identical to
35 hashlittle() except it returns two 32-bit hashes for the price of one.
36 You could implement hashbig2() if you wanted but I haven't bothered here.
38 If you want to find a hash of, say, exactly 7 integers, do
39 a = i1; b = i2; c = i3;
40 mix(a,b,c);
41 a += i4; b += i5; c += i6;
42 mix(a,b,c);
43 a += i7;
44 final(a,b,c);
45 then use c as the hash value. If you have a variable length array of
46 4-byte integers to hash, use hashword(). If you have a byte array (like
47 a character string), use hashlittle(). If you have several byte arrays, or
48 a mix of things, see the comments above hashlittle().
50 Why is this so big? I read 12 bytes at a time into 3 4-byte integers,
51 then mix those integers. This is fast (you can do a lot more thorough
52 mixing with 12*3 instructions on 3 integers than you can with 3 instructions
53 on 1 byte), but shoehorning those bytes into integers efficiently is messy.
56 #include "jhash.h"
59 * My best guess at if you are big-endian or little-endian. This may
60 * need adjustment.
62 #if defined(ROCKBOX_LITTLE_ENDIAN)
63 # define HASH_LITTLE_ENDIAN 1
64 # define HASH_BIG_ENDIAN 0
65 #elif defined(ROCKBOX_BIG_ENDIAN)
66 # define HASH_LITTLE_ENDIAN 0
67 # define HASH_BIG_ENDIAN 1
68 #else
69 # define HASH_LITTLE_ENDIAN 0
70 # define HASH_BIG_ENDIAN 0
71 #endif
73 #define hashsize(n) ((uint32_t)1<<(n))
74 #define hashmask(n) (hashsize(n)-1)
75 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
79 mix -- mix 3 32-bit values reversibly.
81 This is reversible, so any information in (a,b,c) before mix() is
82 still in (a,b,c) after mix().
84 If four pairs of (a,b,c) inputs are run through mix(), or through
85 mix() in reverse, there are at least 32 bits of the output that
86 are sometimes the same for one pair and different for another pair.
87 This was tested for:
88 * pairs that differed by one bit, by two bits, in any combination
89 of top bits of (a,b,c), or in any combination of bottom bits of
90 (a,b,c).
91 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
92 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
93 is commonly produced by subtraction) look like a single 1-bit
94 difference.
95 * the base values were pseudorandom, all zero but one bit set, or
96 all zero plus a counter that starts at zero.
98 Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
99 satisfy this are
100 4 6 8 16 19 4
101 9 15 3 18 27 15
102 14 9 3 7 17 3
103 Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
104 for "differ" defined as + with a one-bit base and a two-bit delta. I
105 used http://burtleburtle.net/bob/hash/avalanche.html to choose
106 the operations, constants, and arrangements of the variables.
108 This does not achieve avalanche. There are input bits of (a,b,c)
109 that fail to affect some output bits of (a,b,c), especially of a. The
110 most thoroughly mixed value is c, but it doesn't really even achieve
111 avalanche in c.
113 This allows some parallelism. Read-after-writes are good at doubling
114 the number of bits affected, so the goal of mixing pulls in the opposite
115 direction as the goal of parallelism. I did what I could. Rotates
116 seem to cost as much as shifts on every machine I could lay my hands
117 on, and rotates are much kinder to the top and bottom bits, so I used
118 rotates.
120 #define mix(a,b,c) \
122 a -= c; a ^= rot(c, 4); c += b; \
123 b -= a; b ^= rot(a, 6); a += c; \
124 c -= b; c ^= rot(b, 8); b += a; \
125 a -= c; a ^= rot(c,16); c += b; \
126 b -= a; b ^= rot(a,19); a += c; \
127 c -= b; c ^= rot(b, 4); b += a; \
131 final -- final mixing of 3 32-bit values (a,b,c) into c
133 Pairs of (a,b,c) values differing in only a few bits will usually
134 produce values of c that look totally different. This was tested for
135 * pairs that differed by one bit, by two bits, in any combination
136 of top bits of (a,b,c), or in any combination of bottom bits of
137 (a,b,c).
138 * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
139 the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
140 is commonly produced by subtraction) look like a single 1-bit
141 difference.
142 * the base values were pseudorandom, all zero but one bit set, or
143 all zero plus a counter that starts at zero.
145 These constants passed:
146 14 11 25 16 4 14 24
147 12 14 25 16 4 14 24
148 and these came close:
149 4 8 15 26 3 22 24
150 10 8 15 26 3 22 24
151 11 8 15 26 3 22 24
153 #define final(a,b,c) \
155 c ^= b; c -= rot(b,14); \
156 a ^= c; a -= rot(c,11); \
157 b ^= a; b -= rot(a,25); \
158 c ^= b; c -= rot(b,16); \
159 a ^= c; a -= rot(c,4); \
160 b ^= a; b -= rot(a,14); \
161 c ^= b; c -= rot(b,24); \
165 k: pointer to the key, an array of uint32_t
166 length: number of elements in the key
167 initval: an initialization value
168 returns the 32-bit hash
170 uint32_t hashw(const uint32_t *k, size_t length, uint32_t initval)
172 uint32_t a, b, c;
174 /* Set up the internal state */
175 a = b = c = 0xdeadbeef + (((uint32_t)length)<<2) + initval;
177 /* handle most of the key */
178 while (length > 3)
180 a += k[0];
181 b += k[1];
182 c += k[2];
183 mix(a,b,c);
184 length -= 3;
185 k += 3;
188 /* handle the last 3 uint32_t's */
189 switch(length) /* all the case statements fall through */
191 case 3:
192 c+=k[2];
193 case 2:
194 b+=k[1];
195 case 1:
196 a+=k[0];
197 final(a,b,c);
198 case 0: /* case 0: nothing left to add */
199 break;
201 /* report the result */
202 return c;
207 hashw2() -- same as hashw(), but take two seeds and return two
208 32-bit values. pc and pb must both be nonnull, and *pc and *pb must
209 both be initialized with seeds. If you pass in (*pb)==0, the output
210 (*pc) will be the same as the return value from hashword().
211 k: pointer to the key, an array of uint32_t
212 length: number of elements in the key
213 pc, pb: pointers to primary and secondary initial values, also used to store
214 the hash results.
216 void hashw2 (const uint32_t *k, size_t length, uint32_t *pc, uint32_t *pb)
218 uint32_t a,b,c;
220 /* Set up the internal state */
221 a = b = c = 0xdeadbeef + ((uint32_t)(length<<2)) + *pc;
222 c += *pb;
224 /* handle most of the key */
225 while (length > 3)
227 a += k[0];
228 b += k[1];
229 c += k[2];
230 mix(a,b,c);
231 length -= 3;
232 k += 3;
235 /* handle the last 3 uint32_t's */
236 switch(length) /* all the case statements fall through */
238 case 3:
239 c+=k[2];
240 case 2:
241 b+=k[1];
242 case 1:
243 a+=k[0];
244 final(a,b,c);
245 case 0: /* case 0: nothing left to add */
246 break;
248 /* report the result */
249 *pc=c; *pb=b;
254 hashs() -- hash a variable-length key into a 32-bit value
255 k: pointer to the key, an array of bytes
256 length: number of elements in the key
257 initval: an initialization value
258 returns the 32-bit hash
259 Returns a 32-bit value. Every bit of the key affects every bit of
260 the return value. Two keys differing by one or two bits will have
261 totally different hash values.
263 The best hash table sizes are powers of 2. There is no need to do
264 mod a prime (mod is sooo slow!). If you need less than 32 bits,
265 use a bitmask. For example, if you need only 10 bits, do
266 h = (h & hashmask(10));
267 In which case, the hash table should have hashsize(10) elements.
269 If you are hashing n strings (uint8_t **)k, do it like this:
270 for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
272 By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
273 code any way you wish, private, educational, or commercial. It's free.
275 Use for hash table lookup, or anything where one collision in 2^^32 is
276 acceptable. Do NOT use for cryptographic purposes.
279 uint32_t hashs( const void *key, size_t length, uint32_t initval)
281 uint32_t a,b,c; /* internal state */
282 union { const void *ptr; size_t i; } u;/* needed for Mac Powerbook G4 */
284 /* Set up the internal state */
285 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
287 u.ptr = key;
288 #if HASH_LITTLE_ENDIAN
289 if ((u.i & 0x3) == 0) {
290 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
292 /* all but last block: aligned reads and affect 32 bits of (a,b,c) */
293 while (length > 12)
295 a += k[0];
296 b += k[1];
297 c += k[2];
298 mix(a,b,c);
299 length -= 12;
300 k += 3;
303 /* handle the last (probably partial) block */
304 switch(length)
306 case 12:
307 c += k[2];
308 b += k[1];
309 a += k[0];
310 break;
311 case 11:
312 c += k[2] & 0xffffff;
313 b += k[1];
314 a += k[0];
315 break;
316 case 10:
317 c += k[2] & 0xffff;
318 b += k[1];
319 a += k[0];
320 break;
321 case 9:
322 c += k[2] & 0xff;
323 b += k[1];
324 a += k[0];
325 break;
326 case 8:
327 b += k[1];
328 a += k[0];
329 break;
330 case 7:
331 b += k[1] & 0xffffff;
332 a += k[0];
333 break;
334 case 6:
335 b += k[1] & 0xffff;
336 a += k[0];
337 break;
338 case 5:
339 b += k[1] & 0xff;
340 a += k[0];
341 break;
342 case 4:
343 a += k[0];
344 break;
345 case 3:
346 a += k[0] & 0xffffff;
347 break;
348 case 2 :
349 a += k[0] & 0xffff;
350 break;
351 case 1:
352 a += k[0] & 0xff;
353 break;
354 case 0:
355 return c; /* zero length strings require no mixing */
358 } else if ((u.i & 0x1) == 0) {
359 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
360 const uint8_t *k8;
362 /* all but last block: aligned reads and different mixing */
363 while (length > 12)
365 a += k[0] + (((uint32_t)k[1])<<16);
366 b += k[2] + (((uint32_t)k[3])<<16);
367 c += k[4] + (((uint32_t)k[5])<<16);
368 mix(a,b,c);
369 length -= 12;
370 k += 6;
373 /* handle the last (probably partial) block */
374 k8 = (const uint8_t *)k;
375 switch(length)
377 case 12:
378 c += k[4] + (((uint32_t)k[5])<<16);
379 b += k[2] + (((uint32_t)k[3])<<16);
380 a += k[0] + (((uint32_t)k[1])<<16);
381 break;
382 case 11:
383 c += ((uint32_t)k8[10])<<16; /* fall through */
384 case 10:
385 c += k[4];
386 b += k[2] + (((uint32_t)k[3])<<16);
387 a += k[0] + (((uint32_t)k[1])<<16);
388 break;
389 case 9:
390 c += k8[8]; /* fall through */
391 case 8:
392 b += k[2] + (((uint32_t)k[3])<<16);
393 a += k[0] + (((uint32_t)k[1])<<16);
394 break;
395 case 7:
396 b += ((uint32_t)k8[6])<<16; /* fall through */
397 case 6:
398 b += k[2];
399 a += k[0] + (((uint32_t)k[1])<<16);
400 break;
401 case 5:
402 b += k8[4]; /* fall through */
403 case 4:
404 a += k[0] + (((uint32_t)k[1])<<16);
405 break;
406 case 3:
407 a += ((uint32_t)k8[2])<<16; /* fall through */
408 case 2:
409 a += k[0];
410 break;
411 case 1:
412 a += k8[0];
413 break;
414 case 0:
415 return c; /* zero length requires no mixing */
418 } else
419 #endif
420 { /* need to read the key one byte at a time */
421 const uint8_t *k = (const uint8_t *)key;
423 /* all but the last block: affect some 32 bits of (a,b,c) */
424 while (length > 12)
426 a += k[0];
427 a += ((uint32_t)k[1])<<8;
428 a += ((uint32_t)k[2])<<16;
429 a += ((uint32_t)k[3])<<24;
430 b += k[4];
431 b += ((uint32_t)k[5])<<8;
432 b += ((uint32_t)k[6])<<16;
433 b += ((uint32_t)k[7])<<24;
434 c += k[8];
435 c += ((uint32_t)k[9])<<8;
436 c += ((uint32_t)k[10])<<16;
437 c += ((uint32_t)k[11])<<24;
438 mix(a,b,c);
439 length -= 12;
440 k += 12;
443 /* last block: affect all 32 bits of (c) */
444 switch(length) /* all the case statements fall through */
446 case 12:
447 c += ((uint32_t)k[11])<<24;
448 case 11:
449 c += ((uint32_t)k[10])<<16;
450 case 10:
451 c += ((uint32_t)k[9])<<8;
452 case 9:
453 c += k[8];
454 case 8:
455 b += ((uint32_t)k[7])<<24;
456 case 7:
457 b += ((uint32_t)k[6])<<16;
458 case 6:
459 b += ((uint32_t)k[5])<<8;
460 case 5:
461 b += k[4];
462 case 4:
463 a += ((uint32_t)k[3])<<24;
464 case 3:
465 a += ((uint32_t)k[2])<<16;
466 case 2:
467 a += ((uint32_t)k[1])<<8;
468 case 1:
469 a +=k [0];
470 break;
471 case 0:
472 return c;
476 final(a,b,c);
477 return c;
482 hashs2: return 2 32-bit hash values
483 k: pointer to the key, an array of bytes
484 length: number of elements in the key
485 pc, pb: pointers to primary and secondary initial values, also used to store
486 the hash results.
487 * This is identical to hashlittle(), except it returns two 32-bit hash
488 * values instead of just one. This is good enough for hash table
489 * lookup with 2^^64 buckets, or if you want a second hash if you're not
490 * happy with the first, or if you want a probably-unique 64-bit ID for
491 * the key. *pc is better mixed than *pb, so use *pc first. If you want
492 * a 64-bit value do something like "*pc + (((uint64_t)*pb)<<32)".
494 void hashs2(const void *key, size_t length, uint32_t *pc, uint32_t *pb)
496 uint32_t a, b, c; /* internal state */
497 union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */
499 /* Set up the internal state */
500 a = b = c = 0xdeadbeef + ((uint32_t)length) + *pc;
501 c += *pb;
503 u.ptr = key;
504 #if HASH_LITTLE_ENDIAN
505 if (((u.i & 0x3) == 0)) {
506 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
508 /* all but last block: aligned reads and affect 32 bits of (a,b,c) */
509 while (length > 12)
511 a += k[0];
512 b += k[1];
513 c += k[2];
514 mix(a,b,c);
515 length -= 12;
516 k += 3;
519 /* handle the last (probably partial) block */
520 switch(length)
522 case 12:
523 c += k[2];
524 b += k[1];
525 a += k[0];
526 break;
527 case 11:
528 c += k[2] & 0xffffff;
529 b += k[1];
530 a += k[0];
531 break;
532 case 10:
533 c += k[2] & 0xffff;
534 b += k[1];
535 a += k[0];
536 break;
537 case 9:
538 c += k[2] & 0xff;
539 b += k[1];
540 a += k[0];
541 break;
542 case 8:
543 b += k[1];
544 a += k[0];
545 break;
546 case 7:
547 b += k[1] & 0xffffff;
548 a += k[0];
549 break;
550 case 6:
551 b += k[1] & 0xffff;
552 a += k[0];
553 break;
554 case 5:
555 b += k[1] & 0xff;
556 a += k[0];
557 break;
558 case 4:
559 a += k[0];
560 break;
561 case 3:
562 a += k[0] & 0xffffff;
563 break;
564 case 2:
565 a += k[0] & 0xffff;
566 break;
567 case 1:
568 a += k[0] & 0xff;
569 break;
570 case 0:
571 *pc=c;
572 *pb=b;
573 return; /* zero length strings require no mixing */
575 } else if (((u.i & 0x1) == 0)) {
576 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
577 const uint8_t *k8;
579 /* all but last block: aligned reads and different mixing */
580 while (length > 12)
582 a += k[0] + (((uint32_t)k[1])<<16);
583 b += k[2] + (((uint32_t)k[3])<<16);
584 c += k[4] + (((uint32_t)k[5])<<16);
585 mix(a,b,c);
586 length -= 12;
587 k += 6;
590 /* handle the last (probably partial) block */
591 k8 = (const uint8_t *)k;
592 switch(length)
594 case 12:
595 c += k[4] + (((uint32_t)k[5])<<16);
596 b += k[2] + (((uint32_t)k[3])<<16);
597 a += k[0] + (((uint32_t)k[1])<<16);
598 break;
599 case 11:
600 c += ((uint32_t)k8[10])<<16; /* fall through */
601 case 10:
602 c += k[4];
603 b += k[2] + (((uint32_t)k[3])<<16);
604 a += k[0] + (((uint32_t)k[1])<<16);
605 break;
606 case 9:
607 c += k8[8]; /* fall through */
608 case 8:
609 b += k[2] + (((uint32_t)k[3])<<16);
610 a += k[0] + (((uint32_t)k[1])<<16);
611 break;
612 case 7:
613 b += ((uint32_t)k8[6])<<16; /* fall through */
614 case 6:
615 b += k[2];
616 a += k[0] + (((uint32_t)k[1])<<16);
617 break;
618 case 5:
619 b += k8[4]; /* fall through */
620 case 4:
621 a += k[0] + (((uint32_t)k[1])<<16);
622 break;
623 case 3:
624 a += ((uint32_t)k8[2])<<16; /* fall through */
625 case 2:
626 a += k[0];
627 break;
628 case 1:
629 a += k8[0];
630 break;
631 case 0:
632 *pc=c;
633 *pb=b;
634 return; /* zero length strings require no mixing */
636 } else
637 #endif
638 { /* need to read the key one byte at a time */
639 const uint8_t *k = (const uint8_t *)key;
641 /* all but the last block: affect some 32 bits of (a,b,c) */
642 while (length > 12)
644 a += k[0];
645 a += ((uint32_t)k[1])<<8;
646 a += ((uint32_t)k[2])<<16;
647 a += ((uint32_t)k[3])<<24;
648 b += k[4];
649 b += ((uint32_t)k[5])<<8;
650 b += ((uint32_t)k[6])<<16;
651 b += ((uint32_t)k[7])<<24;
652 c += k[8];
653 c += ((uint32_t)k[9])<<8;
654 c += ((uint32_t)k[10])<<16;
655 c += ((uint32_t)k[11])<<24;
656 mix(a,b,c);
657 length -= 12;
658 k += 12;
661 /* last block: affect all 32 bits of (c) */
662 switch(length) /* all the case statements fall through */
664 case 12:
665 c += ((uint32_t)k[11]) << 24;
666 case 11:
667 c += ((uint32_t)k[10]) << 16;
668 case 10:
669 c += ((uint32_t)k[9]) << 8;
670 case 9:
671 c += k[8];
672 case 8:
673 b += ((uint32_t)k[7]) << 24;
674 case 7:
675 b += ((uint32_t)k[6]) << 16;
676 case 6:
677 b += ((uint32_t)k[5]) << 8;
678 case 5:
679 b += k[4];
680 case 4:
681 a += ((uint32_t)k[3]) << 24;
682 case 3:
683 a += ((uint32_t)k[2]) << 16;
684 case 2:
685 a += ((uint32_t)k[1]) << 8;
686 case 1:
687 a += k[0];
688 break;
689 case 0:
690 *pc=c;
691 *pb=b;
692 return; /* zero length strings require no mixing */
696 final(a,b,c);
697 *pc=c;
698 *pb=b;