Commit | Line | Data |
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e2eaf477 | 1 | /* An expandable hash tables datatype. |
b1e51b3c | 2 | Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc. |
e2eaf477 ILT |
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., 59 Temple Place - Suite 330, | |
19 | Boston, MA 02111-1307, 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 | ||
5c82d20a ZW |
44 | #ifdef HAVE_STRING_H |
45 | #include <string.h> | |
46 | #endif | |
47 | ||
e2eaf477 ILT |
48 | #include <stdio.h> |
49 | ||
50 | #include "libiberty.h" | |
51 | #include "hashtab.h" | |
52 | ||
e2eaf477 ILT |
53 | /* This macro defines reserved value for empty table entry. */ |
54 | ||
e0f3df8f | 55 | #define EMPTY_ENTRY ((PTR) 0) |
e2eaf477 ILT |
56 | |
57 | /* This macro defines reserved value for table entry which contained | |
58 | a deleted element. */ | |
59 | ||
e0f3df8f | 60 | #define DELETED_ENTRY ((PTR) 1) |
e2eaf477 | 61 | |
eb383413 L |
62 | static unsigned long higher_prime_number PARAMS ((unsigned long)); |
63 | static hashval_t hash_pointer PARAMS ((const void *)); | |
64 | static int eq_pointer PARAMS ((const void *, const void *)); | |
99a4c1bd | 65 | static int htab_expand PARAMS ((htab_t)); |
e0f3df8f | 66 | static PTR *find_empty_slot_for_expand PARAMS ((htab_t, hashval_t)); |
eb383413 L |
67 | |
68 | /* At some point, we could make these be NULL, and modify the | |
69 | hash-table routines to handle NULL specially; that would avoid | |
70 | function-call overhead for the common case of hashing pointers. */ | |
71 | htab_hash htab_hash_pointer = hash_pointer; | |
72 | htab_eq htab_eq_pointer = eq_pointer; | |
73 | ||
5ca0f83d DD |
74 | /* The following function returns a nearest prime number which is |
75 | greater than N, and near a power of two. */ | |
e2eaf477 ILT |
76 | |
77 | static unsigned long | |
b4fe2683 JM |
78 | higher_prime_number (n) |
79 | unsigned long n; | |
e2eaf477 | 80 | { |
5ca0f83d DD |
81 | /* These are primes that are near, but slightly smaller than, a |
82 | power of two. */ | |
e6450fe5 | 83 | static const unsigned long primes[] = { |
b1e51b3c DD |
84 | (unsigned long) 2, |
85 | (unsigned long) 7, | |
86 | (unsigned long) 13, | |
87 | (unsigned long) 31, | |
88 | (unsigned long) 61, | |
89 | (unsigned long) 127, | |
90 | (unsigned long) 251, | |
91 | (unsigned long) 509, | |
92 | (unsigned long) 1021, | |
93 | (unsigned long) 2039, | |
94 | (unsigned long) 4093, | |
95 | (unsigned long) 8191, | |
96 | (unsigned long) 16381, | |
97 | (unsigned long) 32749, | |
98 | (unsigned long) 65521, | |
99 | (unsigned long) 131071, | |
100 | (unsigned long) 262139, | |
101 | (unsigned long) 524287, | |
102 | (unsigned long) 1048573, | |
103 | (unsigned long) 2097143, | |
104 | (unsigned long) 4194301, | |
105 | (unsigned long) 8388593, | |
106 | (unsigned long) 16777213, | |
107 | (unsigned long) 33554393, | |
108 | (unsigned long) 67108859, | |
109 | (unsigned long) 134217689, | |
110 | (unsigned long) 268435399, | |
111 | (unsigned long) 536870909, | |
112 | (unsigned long) 1073741789, | |
113 | (unsigned long) 2147483647, | |
114 | /* 4294967291L */ | |
06b0287c | 115 | ((unsigned long) 2147483647) + ((unsigned long) 2147483644), |
5ca0f83d DD |
116 | }; |
117 | ||
e6450fe5 DD |
118 | const unsigned long *low = &primes[0]; |
119 | const unsigned long *high = &primes[sizeof(primes) / sizeof(primes[0])]; | |
5ca0f83d DD |
120 | |
121 | while (low != high) | |
122 | { | |
e6450fe5 | 123 | const unsigned long *mid = low + (high - low) / 2; |
5ca0f83d DD |
124 | if (n > *mid) |
125 | low = mid + 1; | |
126 | else | |
127 | high = mid; | |
128 | } | |
129 | ||
130 | /* If we've run out of primes, abort. */ | |
131 | if (n > *low) | |
132 | { | |
133 | fprintf (stderr, "Cannot find prime bigger than %lu\n", n); | |
134 | abort (); | |
135 | } | |
136 | ||
137 | return *low; | |
e2eaf477 ILT |
138 | } |
139 | ||
eb383413 L |
140 | /* Returns a hash code for P. */ |
141 | ||
142 | static hashval_t | |
143 | hash_pointer (p) | |
e0f3df8f | 144 | const PTR p; |
eb383413 L |
145 | { |
146 | return (hashval_t) ((long)p >> 3); | |
147 | } | |
148 | ||
149 | /* Returns non-zero if P1 and P2 are equal. */ | |
150 | ||
151 | static int | |
152 | eq_pointer (p1, p2) | |
e0f3df8f HPN |
153 | const PTR p1; |
154 | const PTR p2; | |
eb383413 L |
155 | { |
156 | return p1 == p2; | |
157 | } | |
158 | ||
e2eaf477 ILT |
159 | /* This function creates table with length slightly longer than given |
160 | source length. Created hash table is initiated as empty (all the | |
161 | hash table entries are EMPTY_ENTRY). The function returns the | |
99a4c1bd | 162 | created hash table. Memory allocation must not fail. */ |
e2eaf477 | 163 | |
b4fe2683 JM |
164 | htab_t |
165 | htab_create (size, hash_f, eq_f, del_f) | |
e2eaf477 | 166 | size_t size; |
b4fe2683 JM |
167 | htab_hash hash_f; |
168 | htab_eq eq_f; | |
169 | htab_del del_f; | |
e2eaf477 | 170 | { |
b4fe2683 | 171 | htab_t result; |
e2eaf477 ILT |
172 | |
173 | size = higher_prime_number (size); | |
b4fe2683 | 174 | result = (htab_t) xcalloc (1, sizeof (struct htab)); |
e0f3df8f | 175 | result->entries = (PTR *) xcalloc (size, sizeof (PTR)); |
e2eaf477 | 176 | result->size = size; |
b4fe2683 JM |
177 | result->hash_f = hash_f; |
178 | result->eq_f = eq_f; | |
179 | result->del_f = del_f; | |
99a4c1bd HPN |
180 | result->return_allocation_failure = 0; |
181 | return result; | |
182 | } | |
183 | ||
184 | /* This function creates table with length slightly longer than given | |
185 | source length. The created hash table is initiated as empty (all the | |
186 | hash table entries are EMPTY_ENTRY). The function returns the created | |
187 | hash table. Memory allocation may fail; it may return NULL. */ | |
188 | ||
189 | htab_t | |
190 | htab_try_create (size, hash_f, eq_f, del_f) | |
191 | size_t size; | |
192 | htab_hash hash_f; | |
193 | htab_eq eq_f; | |
194 | htab_del del_f; | |
195 | { | |
196 | htab_t result; | |
197 | ||
198 | size = higher_prime_number (size); | |
199 | result = (htab_t) calloc (1, sizeof (struct htab)); | |
200 | if (result == NULL) | |
201 | return NULL; | |
202 | ||
203 | result->entries = (PTR *) calloc (size, sizeof (PTR)); | |
204 | if (result->entries == NULL) | |
205 | { | |
206 | free (result); | |
207 | return NULL; | |
208 | } | |
209 | ||
210 | result->size = size; | |
211 | result->hash_f = hash_f; | |
212 | result->eq_f = eq_f; | |
213 | result->del_f = del_f; | |
214 | result->return_allocation_failure = 1; | |
e2eaf477 ILT |
215 | return result; |
216 | } | |
217 | ||
218 | /* This function frees all memory allocated for given hash table. | |
219 | Naturally the hash table must already exist. */ | |
220 | ||
221 | void | |
b4fe2683 JM |
222 | htab_delete (htab) |
223 | htab_t htab; | |
e2eaf477 | 224 | { |
b4fe2683 | 225 | int i; |
eb383413 | 226 | |
b4fe2683 JM |
227 | if (htab->del_f) |
228 | for (i = htab->size - 1; i >= 0; i--) | |
eb383413 L |
229 | if (htab->entries[i] != EMPTY_ENTRY |
230 | && htab->entries[i] != DELETED_ENTRY) | |
231 | (*htab->del_f) (htab->entries[i]); | |
b4fe2683 | 232 | |
e2eaf477 ILT |
233 | free (htab->entries); |
234 | free (htab); | |
235 | } | |
236 | ||
237 | /* This function clears all entries in the given hash table. */ | |
238 | ||
239 | void | |
b4fe2683 JM |
240 | htab_empty (htab) |
241 | htab_t htab; | |
242 | { | |
243 | int i; | |
eb383413 | 244 | |
b4fe2683 JM |
245 | if (htab->del_f) |
246 | for (i = htab->size - 1; i >= 0; i--) | |
eb383413 L |
247 | if (htab->entries[i] != EMPTY_ENTRY |
248 | && htab->entries[i] != DELETED_ENTRY) | |
249 | (*htab->del_f) (htab->entries[i]); | |
b4fe2683 | 250 | |
e0f3df8f | 251 | memset (htab->entries, 0, htab->size * sizeof (PTR)); |
b4fe2683 JM |
252 | } |
253 | ||
254 | /* Similar to htab_find_slot, but without several unwanted side effects: | |
255 | - Does not call htab->eq_f when it finds an existing entry. | |
256 | - Does not change the count of elements/searches/collisions in the | |
257 | hash table. | |
258 | This function also assumes there are no deleted entries in the table. | |
259 | HASH is the hash value for the element to be inserted. */ | |
eb383413 | 260 | |
e0f3df8f | 261 | static PTR * |
b4fe2683 JM |
262 | find_empty_slot_for_expand (htab, hash) |
263 | htab_t htab; | |
eb383413 | 264 | hashval_t hash; |
e2eaf477 | 265 | { |
b4fe2683 | 266 | size_t size = htab->size; |
eb383413 | 267 | hashval_t hash2 = 1 + hash % (size - 2); |
b4fe2683 JM |
268 | unsigned int index = hash % size; |
269 | ||
270 | for (;;) | |
271 | { | |
e0f3df8f | 272 | PTR *slot = htab->entries + index; |
eb383413 | 273 | |
b4fe2683 JM |
274 | if (*slot == EMPTY_ENTRY) |
275 | return slot; | |
eb383413 | 276 | else if (*slot == DELETED_ENTRY) |
b4fe2683 JM |
277 | abort (); |
278 | ||
279 | index += hash2; | |
280 | if (index >= size) | |
281 | index -= size; | |
282 | } | |
e2eaf477 ILT |
283 | } |
284 | ||
285 | /* The following function changes size of memory allocated for the | |
286 | entries and repeatedly inserts the table elements. The occupancy | |
287 | of the table after the call will be about 50%. Naturally the hash | |
288 | table must already exist. Remember also that the place of the | |
99a4c1bd HPN |
289 | table entries is changed. If memory allocation failures are allowed, |
290 | this function will return zero, indicating that the table could not be | |
291 | expanded. If all goes well, it will return a non-zero value. */ | |
e2eaf477 | 292 | |
99a4c1bd | 293 | static int |
b4fe2683 JM |
294 | htab_expand (htab) |
295 | htab_t htab; | |
e2eaf477 | 296 | { |
e0f3df8f HPN |
297 | PTR *oentries; |
298 | PTR *olimit; | |
299 | PTR *p; | |
b4fe2683 JM |
300 | |
301 | oentries = htab->entries; | |
302 | olimit = oentries + htab->size; | |
303 | ||
304 | htab->size = higher_prime_number (htab->size * 2); | |
99a4c1bd HPN |
305 | |
306 | if (htab->return_allocation_failure) | |
307 | { | |
308 | PTR *nentries = (PTR *) calloc (htab->size, sizeof (PTR *)); | |
309 | if (nentries == NULL) | |
310 | return 0; | |
311 | htab->entries = nentries; | |
312 | } | |
313 | else | |
314 | htab->entries = (PTR *) xcalloc (htab->size, sizeof (PTR *)); | |
b4fe2683 JM |
315 | |
316 | htab->n_elements -= htab->n_deleted; | |
317 | htab->n_deleted = 0; | |
318 | ||
319 | p = oentries; | |
320 | do | |
321 | { | |
e0f3df8f | 322 | PTR x = *p; |
eb383413 | 323 | |
b4fe2683 JM |
324 | if (x != EMPTY_ENTRY && x != DELETED_ENTRY) |
325 | { | |
e0f3df8f | 326 | PTR *q = find_empty_slot_for_expand (htab, (*htab->hash_f) (x)); |
eb383413 | 327 | |
b4fe2683 JM |
328 | *q = x; |
329 | } | |
eb383413 | 330 | |
b4fe2683 JM |
331 | p++; |
332 | } | |
333 | while (p < olimit); | |
eb383413 | 334 | |
b4fe2683 | 335 | free (oentries); |
99a4c1bd | 336 | return 1; |
e2eaf477 ILT |
337 | } |
338 | ||
b4fe2683 JM |
339 | /* This function searches for a hash table entry equal to the given |
340 | element. It cannot be used to insert or delete an element. */ | |
341 | ||
e0f3df8f | 342 | PTR |
b4fe2683 JM |
343 | htab_find_with_hash (htab, element, hash) |
344 | htab_t htab; | |
e0f3df8f | 345 | const PTR element; |
eb383413 | 346 | hashval_t hash; |
e2eaf477 | 347 | { |
eb383413 L |
348 | unsigned int index; |
349 | hashval_t hash2; | |
b4fe2683 | 350 | size_t size; |
e0f3df8f | 351 | PTR entry; |
e2eaf477 | 352 | |
b4fe2683 JM |
353 | htab->searches++; |
354 | size = htab->size; | |
b4fe2683 JM |
355 | index = hash % size; |
356 | ||
eb383413 L |
357 | entry = htab->entries[index]; |
358 | if (entry == EMPTY_ENTRY | |
359 | || (entry != DELETED_ENTRY && (*htab->eq_f) (entry, element))) | |
360 | return entry; | |
361 | ||
362 | hash2 = 1 + hash % (size - 2); | |
363 | ||
b4fe2683 | 364 | for (;;) |
e2eaf477 | 365 | { |
b4fe2683 JM |
366 | htab->collisions++; |
367 | index += hash2; | |
368 | if (index >= size) | |
369 | index -= size; | |
eb383413 L |
370 | |
371 | entry = htab->entries[index]; | |
372 | if (entry == EMPTY_ENTRY | |
373 | || (entry != DELETED_ENTRY && (*htab->eq_f) (entry, element))) | |
374 | return entry; | |
e2eaf477 | 375 | } |
b4fe2683 JM |
376 | } |
377 | ||
378 | /* Like htab_find_slot_with_hash, but compute the hash value from the | |
379 | element. */ | |
eb383413 | 380 | |
e0f3df8f | 381 | PTR |
b4fe2683 JM |
382 | htab_find (htab, element) |
383 | htab_t htab; | |
e0f3df8f | 384 | const PTR element; |
b4fe2683 JM |
385 | { |
386 | return htab_find_with_hash (htab, element, (*htab->hash_f) (element)); | |
387 | } | |
388 | ||
389 | /* This function searches for a hash table slot containing an entry | |
390 | equal to the given element. To delete an entry, call this with | |
391 | INSERT = 0, then call htab_clear_slot on the slot returned (possibly | |
392 | after doing some checks). To insert an entry, call this with | |
99a4c1bd HPN |
393 | INSERT = 1, then write the value you want into the returned slot. |
394 | When inserting an entry, NULL may be returned if memory allocation | |
395 | fails. */ | |
b4fe2683 | 396 | |
e0f3df8f | 397 | PTR * |
b4fe2683 JM |
398 | htab_find_slot_with_hash (htab, element, hash, insert) |
399 | htab_t htab; | |
e0f3df8f | 400 | const PTR element; |
eb383413 L |
401 | hashval_t hash; |
402 | enum insert_option insert; | |
b4fe2683 | 403 | { |
e0f3df8f | 404 | PTR *first_deleted_slot; |
eb383413 L |
405 | unsigned int index; |
406 | hashval_t hash2; | |
b4fe2683 JM |
407 | size_t size; |
408 | ||
99a4c1bd HPN |
409 | if (insert == INSERT && htab->size * 3 <= htab->n_elements * 4 |
410 | && htab_expand (htab) == 0) | |
411 | return NULL; | |
b4fe2683 JM |
412 | |
413 | size = htab->size; | |
414 | hash2 = 1 + hash % (size - 2); | |
415 | index = hash % size; | |
416 | ||
e2eaf477 | 417 | htab->searches++; |
b4fe2683 JM |
418 | first_deleted_slot = NULL; |
419 | ||
420 | for (;;) | |
e2eaf477 | 421 | { |
e0f3df8f | 422 | PTR entry = htab->entries[index]; |
b4fe2683 JM |
423 | if (entry == EMPTY_ENTRY) |
424 | { | |
eb383413 | 425 | if (insert == NO_INSERT) |
b4fe2683 JM |
426 | return NULL; |
427 | ||
428 | htab->n_elements++; | |
429 | ||
430 | if (first_deleted_slot) | |
e2eaf477 | 431 | { |
b4fe2683 JM |
432 | *first_deleted_slot = EMPTY_ENTRY; |
433 | return first_deleted_slot; | |
e2eaf477 | 434 | } |
b4fe2683 JM |
435 | |
436 | return &htab->entries[index]; | |
437 | } | |
438 | ||
439 | if (entry == DELETED_ENTRY) | |
440 | { | |
441 | if (!first_deleted_slot) | |
442 | first_deleted_slot = &htab->entries[index]; | |
443 | } | |
eb383413 L |
444 | else if ((*htab->eq_f) (entry, element)) |
445 | return &htab->entries[index]; | |
b4fe2683 JM |
446 | |
447 | htab->collisions++; | |
448 | index += hash2; | |
449 | if (index >= size) | |
450 | index -= size; | |
e2eaf477 | 451 | } |
e2eaf477 ILT |
452 | } |
453 | ||
b4fe2683 JM |
454 | /* Like htab_find_slot_with_hash, but compute the hash value from the |
455 | element. */ | |
eb383413 | 456 | |
e0f3df8f | 457 | PTR * |
b4fe2683 JM |
458 | htab_find_slot (htab, element, insert) |
459 | htab_t htab; | |
e0f3df8f | 460 | const PTR element; |
eb383413 | 461 | enum insert_option insert; |
b4fe2683 JM |
462 | { |
463 | return htab_find_slot_with_hash (htab, element, (*htab->hash_f) (element), | |
464 | insert); | |
465 | } | |
466 | ||
467 | /* This function deletes an element with the given value from hash | |
468 | table. If there is no matching element in the hash table, this | |
469 | function does nothing. */ | |
e2eaf477 ILT |
470 | |
471 | void | |
b4fe2683 JM |
472 | htab_remove_elt (htab, element) |
473 | htab_t htab; | |
e0f3df8f | 474 | PTR element; |
e2eaf477 | 475 | { |
e0f3df8f | 476 | PTR *slot; |
b4fe2683 | 477 | |
eb383413 | 478 | slot = htab_find_slot (htab, element, NO_INSERT); |
b4fe2683 JM |
479 | if (*slot == EMPTY_ENTRY) |
480 | return; | |
481 | ||
482 | if (htab->del_f) | |
483 | (*htab->del_f) (*slot); | |
e2eaf477 | 484 | |
b4fe2683 JM |
485 | *slot = DELETED_ENTRY; |
486 | htab->n_deleted++; | |
e2eaf477 ILT |
487 | } |
488 | ||
b4fe2683 JM |
489 | /* This function clears a specified slot in a hash table. It is |
490 | useful when you've already done the lookup and don't want to do it | |
491 | again. */ | |
e2eaf477 ILT |
492 | |
493 | void | |
b4fe2683 JM |
494 | htab_clear_slot (htab, slot) |
495 | htab_t htab; | |
e0f3df8f | 496 | PTR *slot; |
e2eaf477 ILT |
497 | { |
498 | if (slot < htab->entries || slot >= htab->entries + htab->size | |
499 | || *slot == EMPTY_ENTRY || *slot == DELETED_ENTRY) | |
500 | abort (); | |
eb383413 | 501 | |
b4fe2683 JM |
502 | if (htab->del_f) |
503 | (*htab->del_f) (*slot); | |
eb383413 | 504 | |
e2eaf477 | 505 | *slot = DELETED_ENTRY; |
b4fe2683 | 506 | htab->n_deleted++; |
e2eaf477 ILT |
507 | } |
508 | ||
509 | /* This function scans over the entire hash table calling | |
510 | CALLBACK for each live entry. If CALLBACK returns false, | |
511 | the iteration stops. INFO is passed as CALLBACK's second | |
512 | argument. */ | |
513 | ||
514 | void | |
b4fe2683 JM |
515 | htab_traverse (htab, callback, info) |
516 | htab_t htab; | |
517 | htab_trav callback; | |
e0f3df8f | 518 | PTR info; |
e2eaf477 | 519 | { |
e0f3df8f HPN |
520 | PTR *slot = htab->entries; |
521 | PTR *limit = slot + htab->size; | |
eb383413 | 522 | |
b4fe2683 JM |
523 | do |
524 | { | |
e0f3df8f | 525 | PTR x = *slot; |
eb383413 | 526 | |
b4fe2683 JM |
527 | if (x != EMPTY_ENTRY && x != DELETED_ENTRY) |
528 | if (!(*callback) (slot, info)) | |
529 | break; | |
530 | } | |
531 | while (++slot < limit); | |
e2eaf477 ILT |
532 | } |
533 | ||
eb383413 | 534 | /* Return the current size of given hash table. */ |
e2eaf477 ILT |
535 | |
536 | size_t | |
b4fe2683 JM |
537 | htab_size (htab) |
538 | htab_t htab; | |
e2eaf477 ILT |
539 | { |
540 | return htab->size; | |
541 | } | |
542 | ||
eb383413 | 543 | /* Return the current number of elements in given hash table. */ |
e2eaf477 ILT |
544 | |
545 | size_t | |
b4fe2683 JM |
546 | htab_elements (htab) |
547 | htab_t htab; | |
e2eaf477 | 548 | { |
b4fe2683 | 549 | return htab->n_elements - htab->n_deleted; |
e2eaf477 ILT |
550 | } |
551 | ||
eb383413 L |
552 | /* Return the fraction of fixed collisions during all work with given |
553 | hash table. */ | |
e2eaf477 | 554 | |
b4fe2683 JM |
555 | double |
556 | htab_collisions (htab) | |
557 | htab_t htab; | |
e2eaf477 | 558 | { |
eb383413 | 559 | if (htab->searches == 0) |
b4fe2683 | 560 | return 0.0; |
eb383413 L |
561 | |
562 | return (double) htab->collisions / (double) htab->searches; | |
e2eaf477 | 563 | } |
8fc34799 | 564 | |
68a41de7 DD |
565 | /* Hash P as a null-terminated string. |
566 | ||
567 | Copied from gcc/hashtable.c. Zack had the following to say with respect | |
568 | to applicability, though note that unlike hashtable.c, this hash table | |
569 | implementation re-hashes rather than chain buckets. | |
570 | ||
571 | http://gcc.gnu.org/ml/gcc-patches/2001-08/msg01021.html | |
572 | From: Zack Weinberg <zackw@panix.com> | |
573 | Date: Fri, 17 Aug 2001 02:15:56 -0400 | |
574 | ||
575 | I got it by extracting all the identifiers from all the source code | |
576 | I had lying around in mid-1999, and testing many recurrences of | |
577 | the form "H_n = H_{n-1} * K + c_n * L + M" where K, L, M were either | |
578 | prime numbers or the appropriate identity. This was the best one. | |
579 | I don't remember exactly what constituted "best", except I was | |
580 | looking at bucket-length distributions mostly. | |
581 | ||
582 | So it should be very good at hashing identifiers, but might not be | |
583 | as good at arbitrary strings. | |
584 | ||
585 | I'll add that it thoroughly trounces the hash functions recommended | |
586 | for this use at http://burtleburtle.net/bob/hash/index.html, both | |
587 | on speed and bucket distribution. I haven't tried it against the | |
588 | function they just started using for Perl's hashes. */ | |
8fc34799 DD |
589 | |
590 | hashval_t | |
591 | htab_hash_string (p) | |
592 | const PTR p; | |
593 | { | |
594 | const unsigned char *str = (const unsigned char *) p; | |
595 | hashval_t r = 0; | |
596 | unsigned char c; | |
597 | ||
598 | while ((c = *str++) != 0) | |
599 | r = r * 67 + c - 113; | |
600 | ||
601 | return r; | |
602 | } |