1 /* An expandable hash tables datatype.
2    Copyright (C) 1999-2020 Free Software Foundation, Inc.
3    Contributed by Vladimir Makarov (vmakarov@cygnus.com).
4 
5 This file is part of the libiberty library.
6 Libiberty is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Library General Public
8 License as published by the Free Software Foundation; either
9 version 2 of the License, or (at your option) any later version.
10 
11 Libiberty is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14 Library General Public License for more details.
15 
16 You should have received a copy of the GNU Library General Public
17 License along with libiberty; see the file COPYING.LIB.  If
18 not, write to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
19 Boston, MA 02110-1301, USA.  */
20 
21 /* This package implements basic hash table functionality.  It is possible
22    to search for an entry, create an entry and destroy an entry.
23 
24    Elements in the table are generic pointers.
25 
26    The size of the table is not fixed; if the occupancy of the table
27    grows too high the hash table will be expanded.
28 
29    The abstract data implementation is based on generalized Algorithm D
30    from Knuth's book "The art of computer programming".  Hash table is
31    expanded by creation of new hash table and transferring elements from
32    the old table to the new table. */
33 
34 #ifdef HAVE_CONFIG_H
35 #include "config.h"
36 #endif
37 
38 #include <sys/types.h>
39 
40 #ifdef HAVE_STDLIB_H
41 #include <stdlib.h>
42 #endif
43 #ifdef HAVE_STRING_H
44 #include <string.h>
45 #endif
46 #ifdef HAVE_MALLOC_H
47 #include <malloc.h>
48 #endif
49 #ifdef HAVE_LIMITS_H
50 #include <limits.h>
51 #endif
52 #ifdef HAVE_INTTYPES_H
53 #include <inttypes.h>
54 #endif
55 #ifdef HAVE_STDINT_H
56 #include <stdint.h>
57 #endif
58 
59 #include <stdio.h>
60 
61 #include "libiberty.h"
62 #include "ansidecl.h"
63 #include "hashtab.h"
64 
65 #ifndef CHAR_BIT
66 #define CHAR_BIT 8
67 #endif
68 
69 static unsigned int higher_prime_index (unsigned long);
70 static hashval_t htab_mod_1 (hashval_t, hashval_t, hashval_t, int);
71 static hashval_t htab_mod (hashval_t, htab_t);
72 static hashval_t htab_mod_m2 (hashval_t, htab_t);
73 static hashval_t hash_pointer (const void *);
74 static int eq_pointer (const void *, const void *);
75 static int htab_expand (htab_t);
76 static PTR *find_empty_slot_for_expand (htab_t, hashval_t);
77 
78 /* At some point, we could make these be NULL, and modify the
79    hash-table routines to handle NULL specially; that would avoid
80    function-call overhead for the common case of hashing pointers.  */
81 htab_hash htab_hash_pointer = hash_pointer;
82 htab_eq htab_eq_pointer = eq_pointer;
83 
84 /* Table of primes and multiplicative inverses.
85 
86    Note that these are not minimally reduced inverses.  Unlike when generating
87    code to divide by a constant, we want to be able to use the same algorithm
88    all the time.  All of these inverses (are implied to) have bit 32 set.
89 
90    For the record, here's the function that computed the table; it's a
91    vastly simplified version of the function of the same name from gcc.  */
92 
93 #if 0
94 unsigned int
95 ceil_log2 (unsigned int x)
96 {
97   int i;
98   for (i = 31; i >= 0 ; --i)
99     if (x > (1u << i))
100       return i+1;
101   abort ();
102 }
103 
104 unsigned int
105 choose_multiplier (unsigned int d, unsigned int *mlp, unsigned char *shiftp)
106 {
107   unsigned long long mhigh;
108   double nx;
109   int lgup, post_shift;
110   int pow, pow2;
111   int n = 32, precision = 32;
112 
113   lgup = ceil_log2 (d);
114   pow = n + lgup;
115   pow2 = n + lgup - precision;
116 
117   nx = ldexp (1.0, pow) + ldexp (1.0, pow2);
118   mhigh = nx / d;
119 
120   *shiftp = lgup - 1;
121   *mlp = mhigh;
122   return mhigh >> 32;
123 }
124 #endif
125 
126 struct prime_ent
127 {
128   hashval_t prime;
129   hashval_t inv;
130   hashval_t inv_m2;	/* inverse of prime-2 */
131   hashval_t shift;
132 };
133 
134 static struct prime_ent const prime_tab[] = {
135   {          7, 0x24924925, 0x9999999b, 2 },
136   {         13, 0x3b13b13c, 0x745d1747, 3 },
137   {         31, 0x08421085, 0x1a7b9612, 4 },
138   {         61, 0x0c9714fc, 0x15b1e5f8, 5 },
139   {        127, 0x02040811, 0x0624dd30, 6 },
140   {        251, 0x05197f7e, 0x073260a5, 7 },
141   {        509, 0x01824366, 0x02864fc8, 8 },
142   {       1021, 0x00c0906d, 0x014191f7, 9 },
143   {       2039, 0x0121456f, 0x0161e69e, 10 },
144   {       4093, 0x00300902, 0x00501908, 11 },
145   {       8191, 0x00080041, 0x00180241, 12 },
146   {      16381, 0x000c0091, 0x00140191, 13 },
147   {      32749, 0x002605a5, 0x002a06e6, 14 },
148   {      65521, 0x000f00e2, 0x00110122, 15 },
149   {     131071, 0x00008001, 0x00018003, 16 },
150   {     262139, 0x00014002, 0x0001c004, 17 },
151   {     524287, 0x00002001, 0x00006001, 18 },
152   {    1048573, 0x00003001, 0x00005001, 19 },
153   {    2097143, 0x00004801, 0x00005801, 20 },
154   {    4194301, 0x00000c01, 0x00001401, 21 },
155   {    8388593, 0x00001e01, 0x00002201, 22 },
156   {   16777213, 0x00000301, 0x00000501, 23 },
157   {   33554393, 0x00001381, 0x00001481, 24 },
158   {   67108859, 0x00000141, 0x000001c1, 25 },
159   {  134217689, 0x000004e1, 0x00000521, 26 },
160   {  268435399, 0x00000391, 0x000003b1, 27 },
161   {  536870909, 0x00000019, 0x00000029, 28 },
162   { 1073741789, 0x0000008d, 0x00000095, 29 },
163   { 2147483647, 0x00000003, 0x00000007, 30 },
164   /* Avoid "decimal constant so large it is unsigned" for 4294967291.  */
165   { 0xfffffffb, 0x00000006, 0x00000008, 31 }
166 };
167 
168 /* The following function returns an index into the above table of the
169    nearest prime number which is greater than N, and near a power of two. */
170 
171 static unsigned int
172 higher_prime_index (unsigned long n)
173 {
174   unsigned int low = 0;
175   unsigned int high = sizeof(prime_tab) / sizeof(prime_tab[0]);
176 
177   while (low != high)
178     {
179       unsigned int mid = low + (high - low) / 2;
180       if (n > prime_tab[mid].prime)
181 	low = mid + 1;
182       else
183 	high = mid;
184     }
185 
186   /* If we've run out of primes, abort.  */
187   if (n > prime_tab[low].prime)
188     {
189       fprintf (stderr, "Cannot find prime bigger than %lu\n", n);
190       abort ();
191     }
192 
193   return low;
194 }
195 
196 /* Returns non-zero if P1 and P2 are equal.  */
197 
198 static int
199 eq_pointer (const PTR p1, const PTR p2)
200 {
201   return p1 == p2;
202 }
203 
204 
205 /* The parens around the function names in the next two definitions
206    are essential in order to prevent macro expansions of the name.
207    The bodies, however, are expanded as expected, so they are not
208    recursive definitions.  */
209 
210 /* Return the current size of given hash table.  */
211 
212 #define htab_size(htab)  ((htab)->size)
213 
214 size_t
215 (htab_size) (htab_t htab)
216 {
217   return htab_size (htab);
218 }
219 
220 /* Return the current number of elements in given hash table. */
221 
222 #define htab_elements(htab)  ((htab)->n_elements - (htab)->n_deleted)
223 
224 size_t
225 (htab_elements) (htab_t htab)
226 {
227   return htab_elements (htab);
228 }
229 
230 /* Return X % Y.  */
231 
232 static inline hashval_t
233 htab_mod_1 (hashval_t x, hashval_t y, hashval_t inv, int shift)
234 {
235   /* The multiplicative inverses computed above are for 32-bit types, and
236      requires that we be able to compute a highpart multiply.  */
237 #ifdef UNSIGNED_64BIT_TYPE
238   __extension__ typedef UNSIGNED_64BIT_TYPE ull;
239   if (sizeof (hashval_t) * CHAR_BIT <= 32)
240     {
241       hashval_t t1, t2, t3, t4, q, r;
242 
243       t1 = ((ull)x * inv) >> 32;
244       t2 = x - t1;
245       t3 = t2 >> 1;
246       t4 = t1 + t3;
247       q  = t4 >> shift;
248       r  = x - (q * y);
249 
250       return r;
251     }
252 #endif
253 
254   /* Otherwise just use the native division routines.  */
255   return x % y;
256 }
257 
258 /* Compute the primary hash for HASH given HTAB's current size.  */
259 
260 static inline hashval_t
261 htab_mod (hashval_t hash, htab_t htab)
262 {
263   const struct prime_ent *p = &prime_tab[htab->size_prime_index];
264   return htab_mod_1 (hash, p->prime, p->inv, p->shift);
265 }
266 
267 /* Compute the secondary hash for HASH given HTAB's current size.  */
268 
269 static inline hashval_t
270 htab_mod_m2 (hashval_t hash, htab_t htab)
271 {
272   const struct prime_ent *p = &prime_tab[htab->size_prime_index];
273   return 1 + htab_mod_1 (hash, p->prime - 2, p->inv_m2, p->shift);
274 }
275 
276 /* This function creates table with length slightly longer than given
277    source length.  Created hash table is initiated as empty (all the
278    hash table entries are HTAB_EMPTY_ENTRY).  The function returns the
279    created hash table, or NULL if memory allocation fails.  */
280 
281 htab_t
282 htab_create_alloc (size_t size, htab_hash hash_f, htab_eq eq_f,
283                    htab_del del_f, htab_alloc alloc_f, htab_free free_f)
284 {
285   return htab_create_typed_alloc (size, hash_f, eq_f, del_f, alloc_f, alloc_f,
286 				  free_f);
287 }
288 
289 /* As above, but uses the variants of ALLOC_F and FREE_F which accept
290    an extra argument.  */
291 
292 htab_t
293 htab_create_alloc_ex (size_t size, htab_hash hash_f, htab_eq eq_f,
294 		      htab_del del_f, void *alloc_arg,
295 		      htab_alloc_with_arg alloc_f,
296 		      htab_free_with_arg free_f)
297 {
298   htab_t result;
299   unsigned int size_prime_index;
300 
301   size_prime_index = higher_prime_index (size);
302   size = prime_tab[size_prime_index].prime;
303 
304   result = (htab_t) (*alloc_f) (alloc_arg, 1, sizeof (struct htab));
305   if (result == NULL)
306     return NULL;
307   result->entries = (PTR *) (*alloc_f) (alloc_arg, size, sizeof (PTR));
308   if (result->entries == NULL)
309     {
310       if (free_f != NULL)
311 	(*free_f) (alloc_arg, result);
312       return NULL;
313     }
314   result->size = size;
315   result->size_prime_index = size_prime_index;
316   result->hash_f = hash_f;
317   result->eq_f = eq_f;
318   result->del_f = del_f;
319   result->alloc_arg = alloc_arg;
320   result->alloc_with_arg_f = alloc_f;
321   result->free_with_arg_f = free_f;
322   return result;
323 }
324 
325 /*
326 
327 @deftypefn Supplemental htab_t htab_create_typed_alloc (size_t @var{size}, @
328 htab_hash @var{hash_f}, htab_eq @var{eq_f}, htab_del @var{del_f}, @
329 htab_alloc @var{alloc_tab_f}, htab_alloc @var{alloc_f}, @
330 htab_free @var{free_f})
331 
332 This function creates a hash table that uses two different allocators
333 @var{alloc_tab_f} and @var{alloc_f} to use for allocating the table itself
334 and its entries respectively.  This is useful when variables of different
335 types need to be allocated with different allocators.
336 
337 The created hash table is slightly larger than @var{size} and it is
338 initially empty (all the hash table entries are @code{HTAB_EMPTY_ENTRY}).
339 The function returns the created hash table, or @code{NULL} if memory
340 allocation fails.
341 
342 @end deftypefn
343 
344 */
345 
346 htab_t
347 htab_create_typed_alloc (size_t size, htab_hash hash_f, htab_eq eq_f,
348 			 htab_del del_f, htab_alloc alloc_tab_f,
349 			 htab_alloc alloc_f, htab_free free_f)
350 {
351   htab_t result;
352   unsigned int size_prime_index;
353 
354   size_prime_index = higher_prime_index (size);
355   size = prime_tab[size_prime_index].prime;
356 
357   result = (htab_t) (*alloc_tab_f) (1, sizeof (struct htab));
358   if (result == NULL)
359     return NULL;
360   result->entries = (PTR *) (*alloc_f) (size, sizeof (PTR));
361   if (result->entries == NULL)
362     {
363       if (free_f != NULL)
364 	(*free_f) (result);
365       return NULL;
366     }
367   result->size = size;
368   result->size_prime_index = size_prime_index;
369   result->hash_f = hash_f;
370   result->eq_f = eq_f;
371   result->del_f = del_f;
372   result->alloc_f = alloc_f;
373   result->free_f = free_f;
374   return result;
375 }
376 
377 
378 /* Update the function pointers and allocation parameter in the htab_t.  */
379 
380 void
381 htab_set_functions_ex (htab_t htab, htab_hash hash_f, htab_eq eq_f,
382                        htab_del del_f, PTR alloc_arg,
383                        htab_alloc_with_arg alloc_f, htab_free_with_arg free_f)
384 {
385   htab->hash_f = hash_f;
386   htab->eq_f = eq_f;
387   htab->del_f = del_f;
388   htab->alloc_arg = alloc_arg;
389   htab->alloc_with_arg_f = alloc_f;
390   htab->free_with_arg_f = free_f;
391 }
392 
393 /* These functions exist solely for backward compatibility.  */
394 
395 #undef htab_create
396 htab_t
397 htab_create (size_t size, htab_hash hash_f, htab_eq eq_f, htab_del del_f)
398 {
399   return htab_create_alloc (size, hash_f, eq_f, del_f, xcalloc, free);
400 }
401 
402 htab_t
403 htab_try_create (size_t size, htab_hash hash_f, htab_eq eq_f, htab_del del_f)
404 {
405   return htab_create_alloc (size, hash_f, eq_f, del_f, calloc, free);
406 }
407 
408 /* This function frees all memory allocated for given hash table.
409    Naturally the hash table must already exist. */
410 
411 void
412 htab_delete (htab_t htab)
413 {
414   size_t size = htab_size (htab);
415   PTR *entries = htab->entries;
416   int i;
417 
418   if (htab->del_f)
419     for (i = size - 1; i >= 0; i--)
420       if (entries[i] != HTAB_EMPTY_ENTRY && entries[i] != HTAB_DELETED_ENTRY)
421 	(*htab->del_f) (entries[i]);
422 
423   if (htab->free_f != NULL)
424     {
425       (*htab->free_f) (entries);
426       (*htab->free_f) (htab);
427     }
428   else if (htab->free_with_arg_f != NULL)
429     {
430       (*htab->free_with_arg_f) (htab->alloc_arg, entries);
431       (*htab->free_with_arg_f) (htab->alloc_arg, htab);
432     }
433 }
434 
435 /* This function clears all entries in the given hash table.  */
436 
437 void
438 htab_empty (htab_t htab)
439 {
440   size_t size = htab_size (htab);
441   PTR *entries = htab->entries;
442   int i;
443 
444   if (htab->del_f)
445     for (i = size - 1; i >= 0; i--)
446       if (entries[i] != HTAB_EMPTY_ENTRY && entries[i] != HTAB_DELETED_ENTRY)
447 	(*htab->del_f) (entries[i]);
448 
449   /* Instead of clearing megabyte, downsize the table.  */
450   if (size > 1024*1024 / sizeof (PTR))
451     {
452       int nindex = higher_prime_index (1024 / sizeof (PTR));
453       int nsize = prime_tab[nindex].prime;
454 
455       if (htab->free_f != NULL)
456 	(*htab->free_f) (htab->entries);
457       else if (htab->free_with_arg_f != NULL)
458 	(*htab->free_with_arg_f) (htab->alloc_arg, htab->entries);
459       if (htab->alloc_with_arg_f != NULL)
460 	htab->entries = (PTR *) (*htab->alloc_with_arg_f) (htab->alloc_arg, nsize,
461 						           sizeof (PTR *));
462       else
463 	htab->entries = (PTR *) (*htab->alloc_f) (nsize, sizeof (PTR *));
464      htab->size = nsize;
465      htab->size_prime_index = nindex;
466     }
467   else
468     memset (entries, 0, size * sizeof (PTR));
469   htab->n_deleted = 0;
470   htab->n_elements = 0;
471 }
472 
473 /* Similar to htab_find_slot, but without several unwanted side effects:
474     - Does not call htab->eq_f when it finds an existing entry.
475     - Does not change the count of elements/searches/collisions in the
476       hash table.
477    This function also assumes there are no deleted entries in the table.
478    HASH is the hash value for the element to be inserted.  */
479 
480 static PTR *
481 find_empty_slot_for_expand (htab_t htab, hashval_t hash)
482 {
483   hashval_t index = htab_mod (hash, htab);
484   size_t size = htab_size (htab);
485   PTR *slot = htab->entries + index;
486   hashval_t hash2;
487 
488   if (*slot == HTAB_EMPTY_ENTRY)
489     return slot;
490   else if (*slot == HTAB_DELETED_ENTRY)
491     abort ();
492 
493   hash2 = htab_mod_m2 (hash, htab);
494   for (;;)
495     {
496       index += hash2;
497       if (index >= size)
498 	index -= size;
499 
500       slot = htab->entries + index;
501       if (*slot == HTAB_EMPTY_ENTRY)
502 	return slot;
503       else if (*slot == HTAB_DELETED_ENTRY)
504 	abort ();
505     }
506 }
507 
508 /* The following function changes size of memory allocated for the
509    entries and repeatedly inserts the table elements.  The occupancy
510    of the table after the call will be about 50%.  Naturally the hash
511    table must already exist.  Remember also that the place of the
512    table entries is changed.  If memory allocation failures are allowed,
513    this function will return zero, indicating that the table could not be
514    expanded.  If all goes well, it will return a non-zero value.  */
515 
516 static int
517 htab_expand (htab_t htab)
518 {
519   PTR *oentries;
520   PTR *olimit;
521   PTR *p;
522   PTR *nentries;
523   size_t nsize, osize, elts;
524   unsigned int oindex, nindex;
525 
526   oentries = htab->entries;
527   oindex = htab->size_prime_index;
528   osize = htab->size;
529   olimit = oentries + osize;
530   elts = htab_elements (htab);
531 
532   /* Resize only when table after removal of unused elements is either
533      too full or too empty.  */
534   if (elts * 2 > osize || (elts * 8 < osize && osize > 32))
535     {
536       nindex = higher_prime_index (elts * 2);
537       nsize = prime_tab[nindex].prime;
538     }
539   else
540     {
541       nindex = oindex;
542       nsize = osize;
543     }
544 
545   if (htab->alloc_with_arg_f != NULL)
546     nentries = (PTR *) (*htab->alloc_with_arg_f) (htab->alloc_arg, nsize,
547 						  sizeof (PTR *));
548   else
549     nentries = (PTR *) (*htab->alloc_f) (nsize, sizeof (PTR *));
550   if (nentries == NULL)
551     return 0;
552   htab->entries = nentries;
553   htab->size = nsize;
554   htab->size_prime_index = nindex;
555   htab->n_elements -= htab->n_deleted;
556   htab->n_deleted = 0;
557 
558   p = oentries;
559   do
560     {
561       PTR x = *p;
562 
563       if (x != HTAB_EMPTY_ENTRY && x != HTAB_DELETED_ENTRY)
564 	{
565 	  PTR *q = find_empty_slot_for_expand (htab, (*htab->hash_f) (x));
566 
567 	  *q = x;
568 	}
569 
570       p++;
571     }
572   while (p < olimit);
573 
574   if (htab->free_f != NULL)
575     (*htab->free_f) (oentries);
576   else if (htab->free_with_arg_f != NULL)
577     (*htab->free_with_arg_f) (htab->alloc_arg, oentries);
578   return 1;
579 }
580 
581 /* This function searches for a hash table entry equal to the given
582    element.  It cannot be used to insert or delete an element.  */
583 
584 PTR
585 htab_find_with_hash (htab_t htab, const PTR element, hashval_t hash)
586 {
587   hashval_t index, hash2;
588   size_t size;
589   PTR entry;
590 
591   htab->searches++;
592   size = htab_size (htab);
593   index = htab_mod (hash, htab);
594 
595   entry = htab->entries[index];
596   if (entry == HTAB_EMPTY_ENTRY
597       || (entry != HTAB_DELETED_ENTRY && (*htab->eq_f) (entry, element)))
598     return entry;
599 
600   hash2 = htab_mod_m2 (hash, htab);
601   for (;;)
602     {
603       htab->collisions++;
604       index += hash2;
605       if (index >= size)
606 	index -= size;
607 
608       entry = htab->entries[index];
609       if (entry == HTAB_EMPTY_ENTRY
610 	  || (entry != HTAB_DELETED_ENTRY && (*htab->eq_f) (entry, element)))
611 	return entry;
612     }
613 }
614 
615 /* Like htab_find_slot_with_hash, but compute the hash value from the
616    element.  */
617 
618 PTR
619 htab_find (htab_t htab, const PTR element)
620 {
621   return htab_find_with_hash (htab, element, (*htab->hash_f) (element));
622 }
623 
624 /* This function searches for a hash table slot containing an entry
625    equal to the given element.  To delete an entry, call this with
626    insert=NO_INSERT, then call htab_clear_slot on the slot returned
627    (possibly after doing some checks).  To insert an entry, call this
628    with insert=INSERT, then write the value you want into the returned
629    slot.  When inserting an entry, NULL may be returned if memory
630    allocation fails.  */
631 
632 PTR *
633 htab_find_slot_with_hash (htab_t htab, const PTR element,
634                           hashval_t hash, enum insert_option insert)
635 {
636   PTR *first_deleted_slot;
637   hashval_t index, hash2;
638   size_t size;
639   PTR entry;
640 
641   size = htab_size (htab);
642   if (insert == INSERT && size * 3 <= htab->n_elements * 4)
643     {
644       if (htab_expand (htab) == 0)
645 	return NULL;
646       size = htab_size (htab);
647     }
648 
649   index = htab_mod (hash, htab);
650 
651   htab->searches++;
652   first_deleted_slot = NULL;
653 
654   entry = htab->entries[index];
655   if (entry == HTAB_EMPTY_ENTRY)
656     goto empty_entry;
657   else if (entry == HTAB_DELETED_ENTRY)
658     first_deleted_slot = &htab->entries[index];
659   else if ((*htab->eq_f) (entry, element))
660     return &htab->entries[index];
661 
662   hash2 = htab_mod_m2 (hash, htab);
663   for (;;)
664     {
665       htab->collisions++;
666       index += hash2;
667       if (index >= size)
668 	index -= size;
669 
670       entry = htab->entries[index];
671       if (entry == HTAB_EMPTY_ENTRY)
672 	goto empty_entry;
673       else if (entry == HTAB_DELETED_ENTRY)
674 	{
675 	  if (!first_deleted_slot)
676 	    first_deleted_slot = &htab->entries[index];
677 	}
678       else if ((*htab->eq_f) (entry, element))
679 	return &htab->entries[index];
680     }
681 
682  empty_entry:
683   if (insert == NO_INSERT)
684     return NULL;
685 
686   if (first_deleted_slot)
687     {
688       htab->n_deleted--;
689       *first_deleted_slot = HTAB_EMPTY_ENTRY;
690       return first_deleted_slot;
691     }
692 
693   htab->n_elements++;
694   return &htab->entries[index];
695 }
696 
697 /* Like htab_find_slot_with_hash, but compute the hash value from the
698    element.  */
699 
700 PTR *
701 htab_find_slot (htab_t htab, const PTR element, enum insert_option insert)
702 {
703   return htab_find_slot_with_hash (htab, element, (*htab->hash_f) (element),
704 				   insert);
705 }
706 
707 /* This function deletes an element with the given value from hash
708    table (the hash is computed from the element).  If there is no matching
709    element in the hash table, this function does nothing.  */
710 
711 void
712 htab_remove_elt (htab_t htab, PTR element)
713 {
714   htab_remove_elt_with_hash (htab, element, (*htab->hash_f) (element));
715 }
716 
717 
718 /* This function deletes an element with the given value from hash
719    table.  If there is no matching element in the hash table, this
720    function does nothing.  */
721 
722 void
723 htab_remove_elt_with_hash (htab_t htab, PTR element, hashval_t hash)
724 {
725   PTR *slot;
726 
727   slot = htab_find_slot_with_hash (htab, element, hash, NO_INSERT);
728   if (slot == NULL)
729     return;
730 
731   if (htab->del_f)
732     (*htab->del_f) (*slot);
733 
734   *slot = HTAB_DELETED_ENTRY;
735   htab->n_deleted++;
736 }
737 
738 /* This function clears a specified slot in a hash table.  It is
739    useful when you've already done the lookup and don't want to do it
740    again.  */
741 
742 void
743 htab_clear_slot (htab_t htab, PTR *slot)
744 {
745   if (slot < htab->entries || slot >= htab->entries + htab_size (htab)
746       || *slot == HTAB_EMPTY_ENTRY || *slot == HTAB_DELETED_ENTRY)
747     abort ();
748 
749   if (htab->del_f)
750     (*htab->del_f) (*slot);
751 
752   *slot = HTAB_DELETED_ENTRY;
753   htab->n_deleted++;
754 }
755 
756 /* This function scans over the entire hash table calling
757    CALLBACK for each live entry.  If CALLBACK returns false,
758    the iteration stops.  INFO is passed as CALLBACK's second
759    argument.  */
760 
761 void
762 htab_traverse_noresize (htab_t htab, htab_trav callback, PTR info)
763 {
764   PTR *slot;
765   PTR *limit;
766 
767   slot = htab->entries;
768   limit = slot + htab_size (htab);
769 
770   do
771     {
772       PTR x = *slot;
773 
774       if (x != HTAB_EMPTY_ENTRY && x != HTAB_DELETED_ENTRY)
775 	if (!(*callback) (slot, info))
776 	  break;
777     }
778   while (++slot < limit);
779 }
780 
781 /* Like htab_traverse_noresize, but does resize the table when it is
782    too empty to improve effectivity of subsequent calls.  */
783 
784 void
785 htab_traverse (htab_t htab, htab_trav callback, PTR info)
786 {
787   size_t size = htab_size (htab);
788   if (htab_elements (htab) * 8 < size && size > 32)
789     htab_expand (htab);
790 
791   htab_traverse_noresize (htab, callback, info);
792 }
793 
794 /* Return the fraction of fixed collisions during all work with given
795    hash table. */
796 
797 double
798 htab_collisions (htab_t htab)
799 {
800   if (htab->searches == 0)
801     return 0.0;
802 
803   return (double) htab->collisions / (double) htab->searches;
804 }
805 
806 /* Hash P as a null-terminated string.
807 
808    Copied from gcc/hashtable.c.  Zack had the following to say with respect
809    to applicability, though note that unlike hashtable.c, this hash table
810    implementation re-hashes rather than chain buckets.
811 
812    http://gcc.gnu.org/ml/gcc-patches/2001-08/msg01021.html
813    From: Zack Weinberg <zackw@panix.com>
814    Date: Fri, 17 Aug 2001 02:15:56 -0400
815 
816    I got it by extracting all the identifiers from all the source code
817    I had lying around in mid-1999, and testing many recurrences of
818    the form "H_n = H_{n-1} * K + c_n * L + M" where K, L, M were either
819    prime numbers or the appropriate identity.  This was the best one.
820    I don't remember exactly what constituted "best", except I was
821    looking at bucket-length distributions mostly.
822 
823    So it should be very good at hashing identifiers, but might not be
824    as good at arbitrary strings.
825 
826    I'll add that it thoroughly trounces the hash functions recommended
827    for this use at http://burtleburtle.net/bob/hash/index.html, both
828    on speed and bucket distribution.  I haven't tried it against the
829    function they just started using for Perl's hashes.  */
830 
831 hashval_t
832 htab_hash_string (const PTR p)
833 {
834   const unsigned char *str = (const unsigned char *) p;
835   hashval_t r = 0;
836   unsigned char c;
837 
838   while ((c = *str++) != 0)
839     r = r * 67 + c - 113;
840 
841   return r;
842 }
843 
844 /* DERIVED FROM:
845 --------------------------------------------------------------------
846 lookup2.c, by Bob Jenkins, December 1996, Public Domain.
847 hash(), hash2(), hash3, and mix() are externally useful functions.
848 Routines to test the hash are included if SELF_TEST is defined.
849 You can use this free for any purpose.  It has no warranty.
850 --------------------------------------------------------------------
851 */
852 
853 /*
854 --------------------------------------------------------------------
855 mix -- mix 3 32-bit values reversibly.
856 For every delta with one or two bit set, and the deltas of all three
857   high bits or all three low bits, whether the original value of a,b,c
858   is almost all zero or is uniformly distributed,
859 * If mix() is run forward or backward, at least 32 bits in a,b,c
860   have at least 1/4 probability of changing.
861 * If mix() is run forward, every bit of c will change between 1/3 and
862   2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
863 mix() was built out of 36 single-cycle latency instructions in a
864   structure that could supported 2x parallelism, like so:
865       a -= b;
866       a -= c; x = (c>>13);
867       b -= c; a ^= x;
868       b -= a; x = (a<<8);
869       c -= a; b ^= x;
870       c -= b; x = (b>>13);
871       ...
872   Unfortunately, superscalar Pentiums and Sparcs can't take advantage
873   of that parallelism.  They've also turned some of those single-cycle
874   latency instructions into multi-cycle latency instructions.  Still,
875   this is the fastest good hash I could find.  There were about 2^^68
876   to choose from.  I only looked at a billion or so.
877 --------------------------------------------------------------------
878 */
879 /* same, but slower, works on systems that might have 8 byte hashval_t's */
880 #define mix(a,b,c) \
881 { \
882   a -= b; a -= c; a ^= (c>>13); \
883   b -= c; b -= a; b ^= (a<< 8); \
884   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
885   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
886   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
887   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
888   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
889   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
890   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
891 }
892 
893 /*
894 --------------------------------------------------------------------
895 hash() -- hash a variable-length key into a 32-bit value
896   k     : the key (the unaligned variable-length array of bytes)
897   len   : the length of the key, counting by bytes
898   level : can be any 4-byte value
899 Returns a 32-bit value.  Every bit of the key affects every bit of
900 the return value.  Every 1-bit and 2-bit delta achieves avalanche.
901 About 36+6len instructions.
902 
903 The best hash table sizes are powers of 2.  There is no need to do
904 mod a prime (mod is sooo slow!).  If you need less than 32 bits,
905 use a bitmask.  For example, if you need only 10 bits, do
906   h = (h & hashmask(10));
907 In which case, the hash table should have hashsize(10) elements.
908 
909 If you are hashing n strings (ub1 **)k, do it like this:
910   for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
911 
912 By Bob Jenkins, 1996.  bob_jenkins@burtleburtle.net.  You may use this
913 code any way you wish, private, educational, or commercial.  It's free.
914 
915 See http://burtleburtle.net/bob/hash/evahash.html
916 Use for hash table lookup, or anything where one collision in 2^32 is
917 acceptable.  Do NOT use for cryptographic purposes.
918 --------------------------------------------------------------------
919 */
920 
921 hashval_t
922 iterative_hash (const PTR k_in /* the key */,
923                 register size_t  length /* the length of the key */,
924                 register hashval_t initval /* the previous hash, or
925                                               an arbitrary value */)
926 {
927   register const unsigned char *k = (const unsigned char *)k_in;
928   register hashval_t a,b,c,len;
929 
930   /* Set up the internal state */
931   len = length;
932   a = b = 0x9e3779b9;  /* the golden ratio; an arbitrary value */
933   c = initval;           /* the previous hash value */
934 
935   /*---------------------------------------- handle most of the key */
936 #ifndef WORDS_BIGENDIAN
937   /* On a little-endian machine, if the data is 4-byte aligned we can hash
938      by word for better speed.  This gives nondeterministic results on
939      big-endian machines.  */
940   if (sizeof (hashval_t) == 4 && (((size_t)k)&3) == 0)
941     while (len >= 12)    /* aligned */
942       {
943 	a += *(hashval_t *)(k+0);
944 	b += *(hashval_t *)(k+4);
945 	c += *(hashval_t *)(k+8);
946 	mix(a,b,c);
947 	k += 12; len -= 12;
948       }
949   else /* unaligned */
950 #endif
951     while (len >= 12)
952       {
953 	a += (k[0] +((hashval_t)k[1]<<8) +((hashval_t)k[2]<<16) +((hashval_t)k[3]<<24));
954 	b += (k[4] +((hashval_t)k[5]<<8) +((hashval_t)k[6]<<16) +((hashval_t)k[7]<<24));
955 	c += (k[8] +((hashval_t)k[9]<<8) +((hashval_t)k[10]<<16)+((hashval_t)k[11]<<24));
956 	mix(a,b,c);
957 	k += 12; len -= 12;
958       }
959 
960   /*------------------------------------- handle the last 11 bytes */
961   c += length;
962   switch(len)              /* all the case statements fall through */
963     {
964     case 11: c+=((hashval_t)k[10]<<24);	/* fall through */
965     case 10: c+=((hashval_t)k[9]<<16);	/* fall through */
966     case 9 : c+=((hashval_t)k[8]<<8);	/* fall through */
967       /* the first byte of c is reserved for the length */
968     case 8 : b+=((hashval_t)k[7]<<24);	/* fall through */
969     case 7 : b+=((hashval_t)k[6]<<16);	/* fall through */
970     case 6 : b+=((hashval_t)k[5]<<8);	/* fall through */
971     case 5 : b+=k[4];			/* fall through */
972     case 4 : a+=((hashval_t)k[3]<<24);	/* fall through */
973     case 3 : a+=((hashval_t)k[2]<<16);	/* fall through */
974     case 2 : a+=((hashval_t)k[1]<<8);	/* fall through */
975     case 1 : a+=k[0];
976       /* case 0: nothing left to add */
977     }
978   mix(a,b,c);
979   /*-------------------------------------------- report the result */
980   return c;
981 }
982 
983 /* Returns a hash code for pointer P. Simplified version of evahash */
984 
985 static hashval_t
986 hash_pointer (const PTR p)
987 {
988   intptr_t v = (intptr_t) p;
989   unsigned a, b, c;
990 
991   a = b = 0x9e3779b9;
992   a += v >> (sizeof (intptr_t) * CHAR_BIT / 2);
993   b += v & (((intptr_t) 1 << (sizeof (intptr_t) * CHAR_BIT / 2)) - 1);
994   c = 0x42135234;
995   mix (a, b, c);
996   return c;
997 }
998