/* hash - hashing table processing. Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006 Free Software Foundation, Inc. Written by Jim Meyering, 1992. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. This program 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 General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ /* A generic hash table package. */ /* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead of malloc. If you change USE_OBSTACK, you have to recompile! */ #include <config.h> #include "hash.h" #include "xalloc.h" #include <limits.h> #include <stdio.h> #include <stdlib.h> #if USE_OBSTACK # include "obstack.h" # ifndef obstack_chunk_alloc # define obstack_chunk_alloc malloc # endif # ifndef obstack_chunk_free # define obstack_chunk_free free # endif #endif #ifndef SIZE_MAX # define SIZE_MAX ((size_t) -1) #endif struct hash_table { /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1, for a possibility of N_BUCKETS. Among those, N_BUCKETS_USED buckets are not empty, there are N_ENTRIES active entries in the table. */ struct hash_entry *bucket; struct hash_entry const *bucket_limit; size_t n_buckets; size_t n_buckets_used; size_t n_entries; /* Tuning arguments, kept in a physicaly separate structure. */ const Hash_tuning *tuning; /* Three functions are given to `hash_initialize', see the documentation block for this function. In a word, HASHER randomizes a user entry into a number up from 0 up to some maximum minus 1; COMPARATOR returns true if two user entries compare equally; and DATA_FREER is the cleanup function for a user entry. */ Hash_hasher hasher; Hash_comparator comparator; Hash_data_freer data_freer; /* A linked list of freed struct hash_entry structs. */ struct hash_entry *free_entry_list; #if USE_OBSTACK /* Whenever obstacks are used, it is possible to allocate all overflowed entries into a single stack, so they all can be freed in a single operation. It is not clear if the speedup is worth the trouble. */ struct obstack entry_stack; #endif }; /* A hash table contains many internal entries, each holding a pointer to some user provided data (also called a user entry). An entry indistinctly refers to both the internal entry and its associated user entry. A user entry contents may be hashed by a randomization function (the hashing function, or just `hasher' for short) into a number (or `slot') between 0 and the current table size. At each slot position in the hash table, starts a linked chain of entries for which the user data all hash to this slot. A bucket is the collection of all entries hashing to the same slot. A good `hasher' function will distribute entries rather evenly in buckets. In the ideal case, the length of each bucket is roughly the number of entries divided by the table size. Finding the slot for a data is usually done in constant time by the `hasher', and the later finding of a precise entry is linear in time with the size of the bucket. Consequently, a larger hash table size (that is, a larger number of buckets) is prone to yielding shorter chains, *given* the `hasher' function behaves properly. Long buckets slow down the lookup algorithm. One might use big hash table sizes in hope to reduce the average length of buckets, but this might become inordinate, as unused slots in the hash table take some space. The best bet is to make sure you are using a good `hasher' function (beware that those are not that easy to write! :-), and to use a table size larger than the actual number of entries. */ /* If an insertion makes the ratio of nonempty buckets to table size larger than the growth threshold (a number between 0.0 and 1.0), then increase the table size by multiplying by the growth factor (a number greater than 1.0). The growth threshold defaults to 0.8, and the growth factor defaults to 1.414, meaning that the table will have doubled its size every second time 80% of the buckets get used. */ #define DEFAULT_GROWTH_THRESHOLD 0.8 #define DEFAULT_GROWTH_FACTOR 1.414 /* If a deletion empties a bucket and causes the ratio of used buckets to table size to become smaller than the shrink threshold (a number between 0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a number greater than the shrink threshold but smaller than 1.0). The shrink threshold and factor default to 0.0 and 1.0, meaning that the table never shrinks. */ #define DEFAULT_SHRINK_THRESHOLD 0.0 #define DEFAULT_SHRINK_FACTOR 1.0 /* Use this to initialize or reset a TUNING structure to some sensible values. */ static const Hash_tuning default_tuning = { DEFAULT_SHRINK_THRESHOLD, DEFAULT_SHRINK_FACTOR, DEFAULT_GROWTH_THRESHOLD, DEFAULT_GROWTH_FACTOR, false }; /* Information and lookup. */ /* The following few functions provide information about the overall hash table organization: the number of entries, number of buckets and maximum length of buckets. */ /* Return the number of buckets in the hash table. The table size, the total number of buckets (used plus unused), or the maximum number of slots, are the same quantity. */ size_t hash_get_n_buckets (const Hash_table *table) { return table->n_buckets; } /* Return the number of slots in use (non-empty buckets). */ size_t hash_get_n_buckets_used (const Hash_table *table) { return table->n_buckets_used; } /* Return the number of active entries. */ size_t hash_get_n_entries (const Hash_table *table) { return table->n_entries; } /* Return the length of the longest chain (bucket). */ size_t hash_get_max_bucket_length (const Hash_table *table) { struct hash_entry const *bucket; size_t max_bucket_length = 0; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { struct hash_entry const *cursor = bucket; size_t bucket_length = 1; while (cursor = cursor->next, cursor) bucket_length++; if (bucket_length > max_bucket_length) max_bucket_length = bucket_length; } } return max_bucket_length; } /* Do a mild validation of a hash table, by traversing it and checking two statistics. */ bool hash_table_ok (const Hash_table *table) { struct hash_entry const *bucket; size_t n_buckets_used = 0; size_t n_entries = 0; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { struct hash_entry const *cursor = bucket; /* Count bucket head. */ n_buckets_used++; n_entries++; /* Count bucket overflow. */ while (cursor = cursor->next, cursor) n_entries++; } } if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries) return true; return false; } void hash_print_statistics (const Hash_table *table, FILE *stream) { size_t n_entries = hash_get_n_entries (table); size_t n_buckets = hash_get_n_buckets (table); size_t n_buckets_used = hash_get_n_buckets_used (table); size_t max_bucket_length = hash_get_max_bucket_length (table); fprintf (stream, "# entries: %lu\n", (unsigned long int) n_entries); fprintf (stream, "# buckets: %lu\n", (unsigned long int) n_buckets); fprintf (stream, "# buckets used: %lu (%.2f%%)\n", (unsigned long int) n_buckets_used, (100.0 * n_buckets_used) / n_buckets); fprintf (stream, "max bucket length: %lu\n", (unsigned long int) max_bucket_length); } /* If ENTRY matches an entry already in the hash table, return the entry from the table. Otherwise, return NULL. */ void * hash_lookup (const Hash_table *table, const void *entry) { struct hash_entry const *bucket = table->bucket + table->hasher (entry, table->n_buckets); struct hash_entry const *cursor; if (! (bucket < table->bucket_limit)) abort (); if (bucket->data == NULL) return NULL; for (cursor = bucket; cursor; cursor = cursor->next) if (table->comparator (entry, cursor->data)) return cursor->data; return NULL; } /* Walking. */ /* The functions in this page traverse the hash table and process the contained entries. For the traversal to work properly, the hash table should not be resized nor modified while any particular entry is being processed. In particular, entries should not be added or removed. */ /* Return the first data in the table, or NULL if the table is empty. */ void * hash_get_first (const Hash_table *table) { struct hash_entry const *bucket; if (table->n_entries == 0) return NULL; for (bucket = table->bucket; ; bucket++) if (! (bucket < table->bucket_limit)) abort (); else if (bucket->data) return bucket->data; } /* Return the user data for the entry following ENTRY, where ENTRY has been returned by a previous call to either `hash_get_first' or `hash_get_next'. Return NULL if there are no more entries. */ void * hash_get_next (const Hash_table *table, const void *entry) { struct hash_entry const *bucket = table->bucket + table->hasher (entry, table->n_buckets); struct hash_entry const *cursor; if (! (bucket < table->bucket_limit)) abort (); /* Find next entry in the same bucket. */ for (cursor = bucket; cursor; cursor = cursor->next) if (cursor->data == entry && cursor->next) return cursor->next->data; /* Find first entry in any subsequent bucket. */ while (++bucket < table->bucket_limit) if (bucket->data) return bucket->data; /* None found. */ return NULL; } /* Fill BUFFER with pointers to active user entries in the hash table, then return the number of pointers copied. Do not copy more than BUFFER_SIZE pointers. */ size_t hash_get_entries (const Hash_table *table, void **buffer, size_t buffer_size) { size_t counter = 0; struct hash_entry const *bucket; struct hash_entry const *cursor; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { for (cursor = bucket; cursor; cursor = cursor->next) { if (counter >= buffer_size) return counter; buffer[counter++] = cursor->data; } } } return counter; } /* Call a PROCESSOR function for each entry of a hash table, and return the number of entries for which the processor function returned success. A pointer to some PROCESSOR_DATA which will be made available to each call to the processor function. The PROCESSOR accepts two arguments: the first is the user entry being walked into, the second is the value of PROCESSOR_DATA as received. The walking continue for as long as the PROCESSOR function returns nonzero. When it returns zero, the walking is interrupted. */ size_t hash_do_for_each (const Hash_table *table, Hash_processor processor, void *processor_data) { size_t counter = 0; struct hash_entry const *bucket; struct hash_entry const *cursor; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { for (cursor = bucket; cursor; cursor = cursor->next) { if (!(*processor) (cursor->data, processor_data)) return counter; counter++; } } } return counter; } /* Allocation and clean-up. */ /* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1. This is a convenience routine for constructing other hashing functions. */ #if USE_DIFF_HASH /* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm, Software--practice & experience 20, 2 (Feb 1990), 209-224. Good hash algorithms tend to be domain-specific, so what's good for [diffutils'] io.c may not be good for your application." */ size_t hash_string (const char *string, size_t n_buckets) { # define ROTATE_LEFT(Value, Shift) \ ((Value) << (Shift) | (Value) >> ((sizeof (size_t) * CHAR_BIT) - (Shift))) # define HASH_ONE_CHAR(Value, Byte) \ ((Byte) + ROTATE_LEFT (Value, 7)) size_t value = 0; unsigned char ch; for (; (ch = *string); string++) value = HASH_ONE_CHAR (value, ch); return value % n_buckets; # undef ROTATE_LEFT # undef HASH_ONE_CHAR } #else /* not USE_DIFF_HASH */ /* This one comes from `recode', and performs a bit better than the above as per a few experiments. It is inspired from a hashing routine found in the very old Cyber `snoop', itself written in typical Greg Mansfield style. (By the way, what happened to this excellent man? Is he still alive?) */ size_t hash_string (const char *string, size_t n_buckets) { size_t value = 0; unsigned char ch; for (; (ch = *string); string++) value = (value * 31 + ch) % n_buckets; return value; } #endif /* not USE_DIFF_HASH */ /* Return true if CANDIDATE is a prime number. CANDIDATE should be an odd number at least equal to 11. */ static bool is_prime (size_t candidate) { size_t divisor = 3; size_t square = divisor * divisor; while (square < candidate && (candidate % divisor)) { divisor++; square += 4 * divisor; divisor++; } return (candidate % divisor ? true : false); } /* Round a given CANDIDATE number up to the nearest prime, and return that prime. Primes lower than 10 are merely skipped. */ static size_t next_prime (size_t candidate) { /* Skip small primes. */ if (candidate < 10) candidate = 10; /* Make it definitely odd. */ candidate |= 1; while (!is_prime (candidate)) candidate += 2; return candidate; } void hash_reset_tuning (Hash_tuning *tuning) { *tuning = default_tuning; } /* For the given hash TABLE, check the user supplied tuning structure for reasonable values, and return true if there is no gross error with it. Otherwise, definitively reset the TUNING field to some acceptable default in the hash table (that is, the user loses the right of further modifying tuning arguments), and return false. */ static bool check_tuning (Hash_table *table) { const Hash_tuning *tuning = table->tuning; /* Be a bit stricter than mathematics would require, so that rounding errors in size calculations do not cause allocations to fail to grow or shrink as they should. The smallest allocation is 11 (due to next_prime's algorithm), so an epsilon of 0.1 should be good enough. */ float epsilon = 0.1f; if (epsilon < tuning->growth_threshold && tuning->growth_threshold < 1 - epsilon && 1 + epsilon < tuning->growth_factor && 0 <= tuning->shrink_threshold && tuning->shrink_threshold + epsilon < tuning->shrink_factor && tuning->shrink_factor <= 1 && tuning->shrink_threshold + epsilon < tuning->growth_threshold) return true; table->tuning = &default_tuning; return false; } /* Allocate and return a new hash table, or NULL upon failure. The initial number of buckets is automatically selected so as to _guarantee_ that you may insert at least CANDIDATE different user entries before any growth of the hash table size occurs. So, if have a reasonably tight a-priori upper bound on the number of entries you intend to insert in the hash table, you may save some table memory and insertion time, by specifying it here. If the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE argument has its meaning changed to the wanted number of buckets. TUNING points to a structure of user-supplied values, in case some fine tuning is wanted over the default behavior of the hasher. If TUNING is NULL, the default tuning parameters are used instead. The user-supplied HASHER function should be provided. It accepts two arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a slot number for that entry which should be in the range 0..TABLE_SIZE-1. This slot number is then returned. The user-supplied COMPARATOR function should be provided. It accepts two arguments pointing to user data, it then returns true for a pair of entries that compare equal, or false otherwise. This function is internally called on entries which are already known to hash to the same bucket index. The user-supplied DATA_FREER function, when not NULL, may be later called with the user data as an argument, just before the entry containing the data gets freed. This happens from within `hash_free' or `hash_clear'. You should specify this function only if you want these functions to free all of your `data' data. This is typically the case when your data is simply an auxiliary struct that you have malloc'd to aggregate several values. */ Hash_table * hash_initialize (size_t candidate, const Hash_tuning *tuning, Hash_hasher hasher, Hash_comparator comparator, Hash_data_freer data_freer) { Hash_table *table; if (hasher == NULL || comparator == NULL) return NULL; table = malloc (sizeof *table); if (table == NULL) return NULL; if (!tuning) tuning = &default_tuning; table->tuning = tuning; if (!check_tuning (table)) { /* Fail if the tuning options are invalid. This is the only occasion when the user gets some feedback about it. Once the table is created, if the user provides invalid tuning options, we silently revert to using the defaults, and ignore further request to change the tuning options. */ goto fail; } if (!tuning->is_n_buckets) { float new_candidate = candidate / tuning->growth_threshold; if (SIZE_MAX <= new_candidate) goto fail; candidate = new_candidate; } if (xalloc_oversized (candidate, sizeof *table->bucket)) goto fail; table->n_buckets = next_prime (candidate); if (xalloc_oversized (table->n_buckets, sizeof *table->bucket)) goto fail; table->bucket = calloc (table->n_buckets, sizeof *table->bucket); table->bucket_limit = table->bucket + table->n_buckets; table->n_buckets_used = 0; table->n_entries = 0; table->hasher = hasher; table->comparator = comparator; table->data_freer = data_freer; table->free_entry_list = NULL; #if USE_OBSTACK obstack_init (&table->entry_stack); #endif return table; fail: free (table); return NULL; } /* Make all buckets empty, placing any chained entries on the free list. Apply the user-specified function data_freer (if any) to the datas of any affected entries. */ void hash_clear (Hash_table *table) { struct hash_entry *bucket; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { struct hash_entry *cursor; struct hash_entry *next; /* Free the bucket overflow. */ for (cursor = bucket->next; cursor; cursor = next) { if (table->data_freer) (*table->data_freer) (cursor->data); cursor->data = NULL; next = cursor->next; /* Relinking is done one entry at a time, as it is to be expected that overflows are either rare or short. */ cursor->next = table->free_entry_list; table->free_entry_list = cursor; } /* Free the bucket head. */ if (table->data_freer) (*table->data_freer) (bucket->data); bucket->data = NULL; bucket->next = NULL; } } table->n_buckets_used = 0; table->n_entries = 0; } /* Reclaim all storage associated with a hash table. If a data_freer function has been supplied by the user when the hash table was created, this function applies it to the data of each entry before freeing that entry. */ void hash_free (Hash_table *table) { struct hash_entry *bucket; struct hash_entry *cursor; struct hash_entry *next; /* Call the user data_freer function. */ if (table->data_freer && table->n_entries) { for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { if (bucket->data) { for (cursor = bucket; cursor; cursor = cursor->next) { (*table->data_freer) (cursor->data); } } } } #if USE_OBSTACK obstack_free (&table->entry_stack, NULL); #else /* Free all bucket overflowed entries. */ for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { for (cursor = bucket->next; cursor; cursor = next) { next = cursor->next; free (cursor); } } /* Also reclaim the internal list of previously freed entries. */ for (cursor = table->free_entry_list; cursor; cursor = next) { next = cursor->next; free (cursor); } #endif /* Free the remainder of the hash table structure. */ free (table->bucket); free (table); } /* Insertion and deletion. */ /* Get a new hash entry for a bucket overflow, possibly by reclying a previously freed one. If this is not possible, allocate a new one. */ static struct hash_entry * allocate_entry (Hash_table *table) { struct hash_entry *new; if (table->free_entry_list) { new = table->free_entry_list; table->free_entry_list = new->next; } else { #if USE_OBSTACK new = obstack_alloc (&table->entry_stack, sizeof *new); #else new = malloc (sizeof *new); #endif } return new; } /* Free a hash entry which was part of some bucket overflow, saving it for later recycling. */ static void free_entry (Hash_table *table, struct hash_entry *entry) { entry->data = NULL; entry->next = table->free_entry_list; table->free_entry_list = entry; } /* This private function is used to help with insertion and deletion. When ENTRY matches an entry in the table, return a pointer to the corresponding user data and set *BUCKET_HEAD to the head of the selected bucket. Otherwise, return NULL. When DELETE is true and ENTRY matches an entry in the table, unlink the matching entry. */ static void * hash_find_entry (Hash_table *table, const void *entry, struct hash_entry **bucket_head, bool delete) { struct hash_entry *bucket = table->bucket + table->hasher (entry, table->n_buckets); struct hash_entry *cursor; if (! (bucket < table->bucket_limit)) abort (); *bucket_head = bucket; /* Test for empty bucket. */ if (bucket->data == NULL) return NULL; /* See if the entry is the first in the bucket. */ if ((*table->comparator) (entry, bucket->data)) { void *data = bucket->data; if (delete) { if (bucket->next) { struct hash_entry *next = bucket->next; /* Bump the first overflow entry into the bucket head, then save the previous first overflow entry for later recycling. */ *bucket = *next; free_entry (table, next); } else { bucket->data = NULL; } } return data; } /* Scan the bucket overflow. */ for (cursor = bucket; cursor->next; cursor = cursor->next) { if ((*table->comparator) (entry, cursor->next->data)) { void *data = cursor->next->data; if (delete) { struct hash_entry *next = cursor->next; /* Unlink the entry to delete, then save the freed entry for later recycling. */ cursor->next = next->next; free_entry (table, next); } return data; } } /* No entry found. */ return NULL; } /* For an already existing hash table, change the number of buckets through specifying CANDIDATE. The contents of the hash table are preserved. The new number of buckets is automatically selected so as to _guarantee_ that the table may receive at least CANDIDATE different user entries, including those already in the table, before any other growth of the hash table size occurs. If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the exact number of buckets desired. */ bool hash_rehash (Hash_table *table, size_t candidate) { Hash_table *new_table; struct hash_entry *bucket; struct hash_entry *cursor; struct hash_entry *next; new_table = hash_initialize (candidate, table->tuning, table->hasher, table->comparator, table->data_freer); if (new_table == NULL) return false; /* Merely reuse the extra old space into the new table. */ #if USE_OBSTACK obstack_free (&new_table->entry_stack, NULL); new_table->entry_stack = table->entry_stack; #endif new_table->free_entry_list = table->free_entry_list; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) if (bucket->data) for (cursor = bucket; cursor; cursor = next) { void *data = cursor->data; struct hash_entry *new_bucket = (new_table->bucket + new_table->hasher (data, new_table->n_buckets)); if (! (new_bucket < new_table->bucket_limit)) abort (); next = cursor->next; if (new_bucket->data) { if (cursor == bucket) { /* Allocate or recycle an entry, when moving from a bucket header into a bucket overflow. */ struct hash_entry *new_entry = allocate_entry (new_table); if (new_entry == NULL) return false; new_entry->data = data; new_entry->next = new_bucket->next; new_bucket->next = new_entry; } else { /* Merely relink an existing entry, when moving from a bucket overflow into a bucket overflow. */ cursor->next = new_bucket->next; new_bucket->next = cursor; } } else { /* Free an existing entry, when moving from a bucket overflow into a bucket header. Also take care of the simple case of moving from a bucket header into a bucket header. */ new_bucket->data = data; new_table->n_buckets_used++; if (cursor != bucket) free_entry (new_table, cursor); } } free (table->bucket); table->bucket = new_table->bucket; table->bucket_limit = new_table->bucket_limit; table->n_buckets = new_table->n_buckets; table->n_buckets_used = new_table->n_buckets_used; table->free_entry_list = new_table->free_entry_list; /* table->n_entries already holds its value. */ #if USE_OBSTACK table->entry_stack = new_table->entry_stack; #endif free (new_table); return true; } /* If ENTRY matches an entry already in the hash table, return the pointer to the entry from the table. Otherwise, insert ENTRY and return ENTRY. Return NULL if the storage required for insertion cannot be allocated. */ void * hash_insert (Hash_table *table, const void *entry) { void *data; struct hash_entry *bucket; /* The caller cannot insert a NULL entry. */ if (! entry) abort (); /* If there's a matching entry already in the table, return that. */ if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL) return data; /* ENTRY is not matched, it should be inserted. */ if (bucket->data) { struct hash_entry *new_entry = allocate_entry (table); if (new_entry == NULL) return NULL; /* Add ENTRY in the overflow of the bucket. */ new_entry->data = (void *) entry; new_entry->next = bucket->next; bucket->next = new_entry; table->n_entries++; return (void *) entry; } /* Add ENTRY right in the bucket head. */ bucket->data = (void *) entry; table->n_entries++; table->n_buckets_used++; /* If the growth threshold of the buckets in use has been reached, increase the table size and rehash. There's no point in checking the number of entries: if the hashing function is ill-conditioned, rehashing is not likely to improve it. */ if (table->n_buckets_used > table->tuning->growth_threshold * table->n_buckets) { /* Check more fully, before starting real work. If tuning arguments became invalid, the second check will rely on proper defaults. */ check_tuning (table); if (table->n_buckets_used > table->tuning->growth_threshold * table->n_buckets) { const Hash_tuning *tuning = table->tuning; float candidate = (tuning->is_n_buckets ? (table->n_buckets * tuning->growth_factor) : (table->n_buckets * tuning->growth_factor * tuning->growth_threshold)); if (SIZE_MAX <= candidate) return NULL; /* If the rehash fails, arrange to return NULL. */ if (!hash_rehash (table, candidate)) entry = NULL; } } return (void *) entry; } /* If ENTRY is already in the table, remove it and return the just-deleted data (the user may want to deallocate its storage). If ENTRY is not in the table, don't modify the table and return NULL. */ void * hash_delete (Hash_table *table, const void *entry) { void *data; struct hash_entry *bucket; data = hash_find_entry (table, entry, &bucket, true); if (!data) return NULL; table->n_entries--; if (!bucket->data) { table->n_buckets_used--; /* If the shrink threshold of the buckets in use has been reached, rehash into a smaller table. */ if (table->n_buckets_used < table->tuning->shrink_threshold * table->n_buckets) { /* Check more fully, before starting real work. If tuning arguments became invalid, the second check will rely on proper defaults. */ check_tuning (table); if (table->n_buckets_used < table->tuning->shrink_threshold * table->n_buckets) { const Hash_tuning *tuning = table->tuning; size_t candidate = (tuning->is_n_buckets ? table->n_buckets * tuning->shrink_factor : (table->n_buckets * tuning->shrink_factor * tuning->growth_threshold)); hash_rehash (table, candidate); } } } return data; } /* Testing. */ #if TESTING void hash_print (const Hash_table *table) { struct hash_entry const *bucket; for (bucket = table->bucket; bucket < table->bucket_limit; bucket++) { struct hash_entry *cursor; if (bucket) printf ("%lu:\n", (unsigned long int) (bucket - table->bucket)); for (cursor = bucket; cursor; cursor = cursor->next) { char const *s = cursor->data; /* FIXME */ if (s) printf (" %s\n", s); } } } #endif /* TESTING */