hashtab.c
23 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
/* An expandable hash tables datatype.
Copyright (C) 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
Contributed by Vladimir Makarov (vmakarov@cygnus.com).
This file is part of the libiberty library.
Libiberty is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
Libiberty is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with libiberty; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/* This package implements basic hash table functionality. It is possible
to search for an entry, create an entry and destroy an entry.
Elements in the table are generic pointers.
The size of the table is not fixed; if the occupancy of the table
grows too high the hash table will be expanded.
The abstract data implementation is based on generalized Algorithm D
from Knuth's book "The art of computer programming". Hash table is
expanded by creation of new hash table and transferring elements from
the old table to the new table. */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/types.h>
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_MALLOC_H
#include <malloc.h>
#endif
#include <stdio.h>
#include "libiberty.h"
#include "hashtab.h"
/* This macro defines reserved value for empty table entry. */
#define EMPTY_ENTRY ((PTR) 0)
/* This macro defines reserved value for table entry which contained
a deleted element. */
#define DELETED_ENTRY ((PTR) 1)
static unsigned long higher_prime_number PARAMS ((unsigned long));
static hashval_t hash_pointer PARAMS ((const void *));
static int eq_pointer PARAMS ((const void *, const void *));
static int htab_expand PARAMS ((htab_t));
static PTR *find_empty_slot_for_expand PARAMS ((htab_t, hashval_t));
/* At some point, we could make these be NULL, and modify the
hash-table routines to handle NULL specially; that would avoid
function-call overhead for the common case of hashing pointers. */
htab_hash htab_hash_pointer = hash_pointer;
htab_eq htab_eq_pointer = eq_pointer;
/* The following function returns a nearest prime number which is
greater than N, and near a power of two. */
static unsigned long
higher_prime_number (n)
unsigned long n;
{
/* These are primes that are near, but slightly smaller than, a
power of two. */
static const unsigned long primes[] = {
(unsigned long) 7,
(unsigned long) 13,
(unsigned long) 31,
(unsigned long) 61,
(unsigned long) 127,
(unsigned long) 251,
(unsigned long) 509,
(unsigned long) 1021,
(unsigned long) 2039,
(unsigned long) 4093,
(unsigned long) 8191,
(unsigned long) 16381,
(unsigned long) 32749,
(unsigned long) 65521,
(unsigned long) 131071,
(unsigned long) 262139,
(unsigned long) 524287,
(unsigned long) 1048573,
(unsigned long) 2097143,
(unsigned long) 4194301,
(unsigned long) 8388593,
(unsigned long) 16777213,
(unsigned long) 33554393,
(unsigned long) 67108859,
(unsigned long) 134217689,
(unsigned long) 268435399,
(unsigned long) 536870909,
(unsigned long) 1073741789,
(unsigned long) 2147483647,
/* 4294967291L */
((unsigned long) 2147483647) + ((unsigned long) 2147483644),
};
const unsigned long *low = &primes[0];
const unsigned long *high = &primes[sizeof(primes) / sizeof(primes[0])];
while (low != high)
{
const unsigned long *mid = low + (high - low) / 2;
if (n > *mid)
low = mid + 1;
else
high = mid;
}
/* If we've run out of primes, abort. */
if (n > *low)
{
fprintf (stderr, "Cannot find prime bigger than %lu\n", n);
abort ();
}
return *low;
}
/* Returns a hash code for P. */
static hashval_t
hash_pointer (p)
const PTR p;
{
return (hashval_t) ((long)p >> 3);
}
/* Returns non-zero if P1 and P2 are equal. */
static int
eq_pointer (p1, p2)
const PTR p1;
const PTR p2;
{
return p1 == p2;
}
/* This function creates table with length slightly longer than given
source length. Created hash table is initiated as empty (all the
hash table entries are EMPTY_ENTRY). The function returns the
created hash table, or NULL if memory allocation fails. */
htab_t
htab_create_alloc (size, hash_f, eq_f, del_f, alloc_f, free_f)
size_t size;
htab_hash hash_f;
htab_eq eq_f;
htab_del del_f;
htab_alloc alloc_f;
htab_free free_f;
{
htab_t result;
size = higher_prime_number (size);
result = (htab_t) (*alloc_f) (1, sizeof (struct htab));
if (result == NULL)
return NULL;
result->entries = (PTR *) (*alloc_f) (size, sizeof (PTR));
if (result->entries == NULL)
{
if (free_f != NULL)
(*free_f) (result);
return NULL;
}
result->size = size;
result->hash_f = hash_f;
result->eq_f = eq_f;
result->del_f = del_f;
result->alloc_f = alloc_f;
result->free_f = free_f;
return result;
}
/* As above, but use the variants of alloc_f and free_f which accept
an extra argument. */
htab_t
htab_create_alloc_ex (size, hash_f, eq_f, del_f, alloc_arg, alloc_f,
free_f)
size_t size;
htab_hash hash_f;
htab_eq eq_f;
htab_del del_f;
PTR alloc_arg;
htab_alloc_with_arg alloc_f;
htab_free_with_arg free_f;
{
htab_t result;
size = higher_prime_number (size);
result = (htab_t) (*alloc_f) (alloc_arg, 1, sizeof (struct htab));
if (result == NULL)
return NULL;
result->entries = (PTR *) (*alloc_f) (alloc_arg, size, sizeof (PTR));
if (result->entries == NULL)
{
if (free_f != NULL)
(*free_f) (alloc_arg, result);
return NULL;
}
result->size = size;
result->hash_f = hash_f;
result->eq_f = eq_f;
result->del_f = del_f;
result->alloc_arg = alloc_arg;
result->alloc_with_arg_f = alloc_f;
result->free_with_arg_f = free_f;
return result;
}
/* Update the function pointers and allocation parameter in the htab_t. */
void
htab_set_functions_ex (htab, hash_f, eq_f, del_f, alloc_arg, alloc_f, free_f)
htab_t htab;
htab_hash hash_f;
htab_eq eq_f;
htab_del del_f;
PTR alloc_arg;
htab_alloc_with_arg alloc_f;
htab_free_with_arg free_f;
{
htab->hash_f = hash_f;
htab->eq_f = eq_f;
htab->del_f = del_f;
htab->alloc_arg = alloc_arg;
htab->alloc_with_arg_f = alloc_f;
htab->free_with_arg_f = free_f;
}
/* These functions exist solely for backward compatibility. */
#undef htab_create
htab_t
htab_create (size, hash_f, eq_f, del_f)
size_t size;
htab_hash hash_f;
htab_eq eq_f;
htab_del del_f;
{
return htab_create_alloc (size, hash_f, eq_f, del_f, xcalloc, free);
}
htab_t
htab_try_create (size, hash_f, eq_f, del_f)
size_t size;
htab_hash hash_f;
htab_eq eq_f;
htab_del del_f;
{
return htab_create_alloc (size, hash_f, eq_f, del_f, calloc, free);
}
/* This function frees all memory allocated for given hash table.
Naturally the hash table must already exist. */
void
htab_delete (htab)
htab_t htab;
{
int i;
if (htab->del_f)
for (i = htab->size - 1; i >= 0; i--)
if (htab->entries[i] != EMPTY_ENTRY
&& htab->entries[i] != DELETED_ENTRY)
(*htab->del_f) (htab->entries[i]);
if (htab->free_f != NULL)
{
(*htab->free_f) (htab->entries);
(*htab->free_f) (htab);
}
else if (htab->free_with_arg_f != NULL)
{
(*htab->free_with_arg_f) (htab->alloc_arg, htab->entries);
(*htab->free_with_arg_f) (htab->alloc_arg, htab);
}
}
/* This function clears all entries in the given hash table. */
void
htab_empty (htab)
htab_t htab;
{
int i;
if (htab->del_f)
for (i = htab->size - 1; i >= 0; i--)
if (htab->entries[i] != EMPTY_ENTRY
&& htab->entries[i] != DELETED_ENTRY)
(*htab->del_f) (htab->entries[i]);
memset (htab->entries, 0, htab->size * sizeof (PTR));
}
/* Similar to htab_find_slot, but without several unwanted side effects:
- Does not call htab->eq_f when it finds an existing entry.
- Does not change the count of elements/searches/collisions in the
hash table.
This function also assumes there are no deleted entries in the table.
HASH is the hash value for the element to be inserted. */
static PTR *
find_empty_slot_for_expand (htab, hash)
htab_t htab;
hashval_t hash;
{
size_t size = htab->size;
unsigned int index = hash % size;
PTR *slot = htab->entries + index;
hashval_t hash2;
if (*slot == EMPTY_ENTRY)
return slot;
else if (*slot == DELETED_ENTRY)
abort ();
hash2 = 1 + hash % (size - 2);
for (;;)
{
index += hash2;
if (index >= size)
index -= size;
slot = htab->entries + index;
if (*slot == EMPTY_ENTRY)
return slot;
else if (*slot == DELETED_ENTRY)
abort ();
}
}
/* The following function changes size of memory allocated for the
entries and repeatedly inserts the table elements. The occupancy
of the table after the call will be about 50%. Naturally the hash
table must already exist. Remember also that the place of the
table entries is changed. If memory allocation failures are allowed,
this function will return zero, indicating that the table could not be
expanded. If all goes well, it will return a non-zero value. */
static int
htab_expand (htab)
htab_t htab;
{
PTR *oentries;
PTR *olimit;
PTR *p;
PTR *nentries;
size_t nsize;
oentries = htab->entries;
olimit = oentries + htab->size;
/* Resize only when table after removal of unused elements is either
too full or too empty. */
if ((htab->n_elements - htab->n_deleted) * 2 > htab->size
|| ((htab->n_elements - htab->n_deleted) * 8 < htab->size
&& htab->size > 32))
nsize = higher_prime_number ((htab->n_elements - htab->n_deleted) * 2);
else
nsize = htab->size;
if (htab->alloc_with_arg_f != NULL)
nentries = (PTR *) (*htab->alloc_with_arg_f) (htab->alloc_arg, nsize,
sizeof (PTR *));
else
nentries = (PTR *) (*htab->alloc_f) (nsize, sizeof (PTR *));
if (nentries == NULL)
return 0;
htab->entries = nentries;
htab->size = nsize;
htab->n_elements -= htab->n_deleted;
htab->n_deleted = 0;
p = oentries;
do
{
PTR x = *p;
if (x != EMPTY_ENTRY && x != DELETED_ENTRY)
{
PTR *q = find_empty_slot_for_expand (htab, (*htab->hash_f) (x));
*q = x;
}
p++;
}
while (p < olimit);
if (htab->free_f != NULL)
(*htab->free_f) (oentries);
else if (htab->free_with_arg_f != NULL)
(*htab->free_with_arg_f) (htab->alloc_arg, oentries);
return 1;
}
/* This function searches for a hash table entry equal to the given
element. It cannot be used to insert or delete an element. */
PTR
htab_find_with_hash (htab, element, hash)
htab_t htab;
const PTR element;
hashval_t hash;
{
unsigned int index;
hashval_t hash2;
size_t size;
PTR entry;
htab->searches++;
size = htab->size;
index = hash % size;
entry = htab->entries[index];
if (entry == EMPTY_ENTRY
|| (entry != DELETED_ENTRY && (*htab->eq_f) (entry, element)))
return entry;
hash2 = 1 + hash % (size - 2);
for (;;)
{
htab->collisions++;
index += hash2;
if (index >= size)
index -= size;
entry = htab->entries[index];
if (entry == EMPTY_ENTRY
|| (entry != DELETED_ENTRY && (*htab->eq_f) (entry, element)))
return entry;
}
}
/* Like htab_find_slot_with_hash, but compute the hash value from the
element. */
PTR
htab_find (htab, element)
htab_t htab;
const PTR element;
{
return htab_find_with_hash (htab, element, (*htab->hash_f) (element));
}
/* This function searches for a hash table slot containing an entry
equal to the given element. To delete an entry, call this with
INSERT = 0, then call htab_clear_slot on the slot returned (possibly
after doing some checks). To insert an entry, call this with
INSERT = 1, then write the value you want into the returned slot.
When inserting an entry, NULL may be returned if memory allocation
fails. */
PTR *
htab_find_slot_with_hash (htab, element, hash, insert)
htab_t htab;
const PTR element;
hashval_t hash;
enum insert_option insert;
{
PTR *first_deleted_slot;
unsigned int index;
hashval_t hash2;
size_t size;
PTR entry;
if (insert == INSERT && htab->size * 3 <= htab->n_elements * 4
&& htab_expand (htab) == 0)
return NULL;
size = htab->size;
index = hash % size;
htab->searches++;
first_deleted_slot = NULL;
entry = htab->entries[index];
if (entry == EMPTY_ENTRY)
goto empty_entry;
else if (entry == DELETED_ENTRY)
first_deleted_slot = &htab->entries[index];
else if ((*htab->eq_f) (entry, element))
return &htab->entries[index];
hash2 = 1 + hash % (size - 2);
for (;;)
{
htab->collisions++;
index += hash2;
if (index >= size)
index -= size;
entry = htab->entries[index];
if (entry == EMPTY_ENTRY)
goto empty_entry;
else if (entry == DELETED_ENTRY)
{
if (!first_deleted_slot)
first_deleted_slot = &htab->entries[index];
}
else if ((*htab->eq_f) (entry, element))
return &htab->entries[index];
}
empty_entry:
if (insert == NO_INSERT)
return NULL;
htab->n_elements++;
if (first_deleted_slot)
{
*first_deleted_slot = EMPTY_ENTRY;
return first_deleted_slot;
}
return &htab->entries[index];
}
/* Like htab_find_slot_with_hash, but compute the hash value from the
element. */
PTR *
htab_find_slot (htab, element, insert)
htab_t htab;
const PTR element;
enum insert_option insert;
{
return htab_find_slot_with_hash (htab, element, (*htab->hash_f) (element),
insert);
}
/* This function deletes an element with the given value from hash
table. If there is no matching element in the hash table, this
function does nothing. */
void
htab_remove_elt (htab, element)
htab_t htab;
PTR element;
{
PTR *slot;
slot = htab_find_slot (htab, element, NO_INSERT);
if (*slot == EMPTY_ENTRY)
return;
if (htab->del_f)
(*htab->del_f) (*slot);
*slot = DELETED_ENTRY;
htab->n_deleted++;
}
/* This function clears a specified slot in a hash table. It is
useful when you've already done the lookup and don't want to do it
again. */
void
htab_clear_slot (htab, slot)
htab_t htab;
PTR *slot;
{
if (slot < htab->entries || slot >= htab->entries + htab->size
|| *slot == EMPTY_ENTRY || *slot == DELETED_ENTRY)
abort ();
if (htab->del_f)
(*htab->del_f) (*slot);
*slot = DELETED_ENTRY;
htab->n_deleted++;
}
/* This function scans over the entire hash table calling
CALLBACK for each live entry. If CALLBACK returns false,
the iteration stops. INFO is passed as CALLBACK's second
argument. */
void
htab_traverse_noresize (htab, callback, info)
htab_t htab;
htab_trav callback;
PTR info;
{
PTR *slot;
PTR *limit;
slot = htab->entries;
limit = slot + htab->size;
do
{
PTR x = *slot;
if (x != EMPTY_ENTRY && x != DELETED_ENTRY)
if (!(*callback) (slot, info))
break;
}
while (++slot < limit);
}
/* Like htab_traverse_noresize, but does resize the table when it is
too empty to improve effectivity of subsequent calls. */
void
htab_traverse (htab, callback, info)
htab_t htab;
htab_trav callback;
PTR info;
{
if ((htab->n_elements - htab->n_deleted) * 8 < htab->size)
htab_expand (htab);
htab_traverse_noresize (htab, callback, info);
}
/* Return the current size of given hash table. */
size_t
htab_size (htab)
htab_t htab;
{
return htab->size;
}
/* Return the current number of elements in given hash table. */
size_t
htab_elements (htab)
htab_t htab;
{
return htab->n_elements - htab->n_deleted;
}
/* Return the fraction of fixed collisions during all work with given
hash table. */
double
htab_collisions (htab)
htab_t htab;
{
if (htab->searches == 0)
return 0.0;
return (double) htab->collisions / (double) htab->searches;
}
/* Hash P as a null-terminated string.
Copied from gcc/hashtable.c. Zack had the following to say with respect
to applicability, though note that unlike hashtable.c, this hash table
implementation re-hashes rather than chain buckets.
http://gcc.gnu.org/ml/gcc-patches/2001-08/msg01021.html
From: Zack Weinberg <zackw@panix.com>
Date: Fri, 17 Aug 2001 02:15:56 -0400
I got it by extracting all the identifiers from all the source code
I had lying around in mid-1999, and testing many recurrences of
the form "H_n = H_{n-1} * K + c_n * L + M" where K, L, M were either
prime numbers or the appropriate identity. This was the best one.
I don't remember exactly what constituted "best", except I was
looking at bucket-length distributions mostly.
So it should be very good at hashing identifiers, but might not be
as good at arbitrary strings.
I'll add that it thoroughly trounces the hash functions recommended
for this use at http://burtleburtle.net/bob/hash/index.html, both
on speed and bucket distribution. I haven't tried it against the
function they just started using for Perl's hashes. */
hashval_t
htab_hash_string (p)
const PTR p;
{
const unsigned char *str = (const unsigned char *) p;
hashval_t r = 0;
unsigned char c;
while ((c = *str++) != 0)
r = r * 67 + c - 113;
return r;
}
/* DERIVED FROM:
--------------------------------------------------------------------
lookup2.c, by Bob Jenkins, December 1996, Public Domain.
hash(), hash2(), hash3, and mix() are externally useful functions.
Routines to test the hash are included if SELF_TEST is defined.
You can use this free for any purpose. It has no warranty.
--------------------------------------------------------------------
*/
/*
--------------------------------------------------------------------
mix -- mix 3 32-bit values reversibly.
For every delta with one or two bit set, and the deltas of all three
high bits or all three low bits, whether the original value of a,b,c
is almost all zero or is uniformly distributed,
* If mix() is run forward or backward, at least 32 bits in a,b,c
have at least 1/4 probability of changing.
* If mix() is run forward, every bit of c will change between 1/3 and
2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
mix() was built out of 36 single-cycle latency instructions in a
structure that could supported 2x parallelism, like so:
a -= b;
a -= c; x = (c>>13);
b -= c; a ^= x;
b -= a; x = (a<<8);
c -= a; b ^= x;
c -= b; x = (b>>13);
...
Unfortunately, superscalar Pentiums and Sparcs can't take advantage
of that parallelism. They've also turned some of those single-cycle
latency instructions into multi-cycle latency instructions. Still,
this is the fastest good hash I could find. There were about 2^^68
to choose from. I only looked at a billion or so.
--------------------------------------------------------------------
*/
/* same, but slower, works on systems that might have 8 byte hashval_t's */
#define mix(a,b,c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<< 8); \
c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
}
/*
--------------------------------------------------------------------
hash() -- hash a variable-length key into a 32-bit value
k : the key (the unaligned variable-length array of bytes)
len : the length of the key, counting by bytes
level : can be any 4-byte value
Returns a 32-bit value. Every bit of the key affects every bit of
the return value. Every 1-bit and 2-bit delta achieves avalanche.
About 36+6len instructions.
The best hash table sizes are powers of 2. There is no need to do
mod a prime (mod is sooo slow!). If you need less than 32 bits,
use a bitmask. For example, if you need only 10 bits, do
h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.
If you are hashing n strings (ub1 **)k, do it like this:
for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
code any way you wish, private, educational, or commercial. It's free.
See http://burtleburtle.net/bob/hash/evahash.html
Use for hash table lookup, or anything where one collision in 2^32 is
acceptable. Do NOT use for cryptographic purposes.
--------------------------------------------------------------------
*/
hashval_t iterative_hash (k_in, length, initval)
const PTR k_in; /* the key */
register size_t length; /* the length of the key */
register hashval_t initval; /* the previous hash, or an arbitrary value */
{
register const unsigned char *k = (const unsigned char *)k_in;
register hashval_t a,b,c,len;
/* Set up the internal state */
len = length;
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = initval; /* the previous hash value */
/*---------------------------------------- handle most of the key */
#ifndef WORDS_BIGENDIAN
/* On a little-endian machine, if the data is 4-byte aligned we can hash
by word for better speed. This gives nondeterministic results on
big-endian machines. */
if (sizeof (hashval_t) == 4 && (((size_t)k)&3) == 0)
while (len >= 12) /* aligned */
{
a += *(hashval_t *)(k+0);
b += *(hashval_t *)(k+4);
c += *(hashval_t *)(k+8);
mix(a,b,c);
k += 12; len -= 12;
}
else /* unaligned */
#endif
while (len >= 12)
{
a += (k[0] +((hashval_t)k[1]<<8) +((hashval_t)k[2]<<16) +((hashval_t)k[3]<<24));
b += (k[4] +((hashval_t)k[5]<<8) +((hashval_t)k[6]<<16) +((hashval_t)k[7]<<24));
c += (k[8] +((hashval_t)k[9]<<8) +((hashval_t)k[10]<<16)+((hashval_t)k[11]<<24));
mix(a,b,c);
k += 12; len -= 12;
}
/*------------------------------------- handle the last 11 bytes */
c += length;
switch(len) /* all the case statements fall through */
{
case 11: c+=((hashval_t)k[10]<<24);
case 10: c+=((hashval_t)k[9]<<16);
case 9 : c+=((hashval_t)k[8]<<8);
/* the first byte of c is reserved for the length */
case 8 : b+=((hashval_t)k[7]<<24);
case 7 : b+=((hashval_t)k[6]<<16);
case 6 : b+=((hashval_t)k[5]<<8);
case 5 : b+=k[4];
case 4 : a+=((hashval_t)k[3]<<24);
case 3 : a+=((hashval_t)k[2]<<16);
case 2 : a+=((hashval_t)k[1]<<8);
case 1 : a+=k[0];
/* case 0: nothing left to add */
}
mix(a,b,c);
/*-------------------------------------------- report the result */
return c;
}