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Diffstat (limited to 'libiberty/hashtab.c')
| -rw-r--r-- | libiberty/hashtab.c | 330 |
1 files changed, 330 insertions, 0 deletions
diff --git a/libiberty/hashtab.c b/libiberty/hashtab.c new file mode 100644 index 00000000000..3f5b3030422 --- /dev/null +++ b/libiberty/hashtab.c @@ -0,0 +1,330 @@ +/* An expandable hash tables datatype. + Copyright (C) 1999 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 + +#include <stdio.h> + +#include "libiberty.h" +#include "hashtab.h" + +/* The following variable is used for debugging. Its value is number + of all calls of `find_hash_table_entry' for all hash tables. */ + +static int all_searches = 0; + +/* The following variable is used for debugging. Its value is number + of collisions fixed for time of work with all hash tables. */ + +static int all_collisions = 0; + +/* The following variable is used for debugging. Its value is number + of all table expansions fixed for time of work with all hash + tables. */ + +static int all_expansions = 0; + +/* This macro defines reserved value for empty table entry. */ + +#define EMPTY_ENTRY NULL + +/* This macro defines reserved value for table entry which contained + a deleted element. */ + +#define DELETED_ENTRY ((void *) 1) + +/* The following function returns the nearest prime number which is + greater than given source number. */ + +static unsigned long +higher_prime_number (number) + unsigned long number; +{ + unsigned long i; + + for (number = (number / 2) * 2 + 3;; number += 2) + { + for (i = 3; i * i <= number; i += 2) + if (number % i == 0) + break; + if (i * i > number) + return number; + } +} + +/* 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. */ + +hash_table_t +create_hash_table (size, hash_function, eq_function) + size_t size; + unsigned (*hash_function) PARAMS ((hash_table_entry_t)); + int (*eq_function) PARAMS ((hash_table_entry_t, hash_table_entry_t)); +{ + hash_table_t result; + + size = higher_prime_number (size); + result = (hash_table_t) xmalloc (sizeof (*result)); + result->entries + = (hash_table_entry_t *) xmalloc (size * sizeof (hash_table_entry_t)); + result->size = size; + result->hash_function = hash_function; + result->eq_function = eq_function; + result->number_of_elements = 0; + result->number_of_deleted_elements = 0; + result->searches = 0; + result->collisions = 0; + memset (result->entries, 0, size * sizeof (hash_table_entry_t)); + return result; +} + +/* This function frees all memory allocated for given hash table. + Naturally the hash table must already exist. */ + +void +delete_hash_table (htab) + hash_table_t htab; +{ + free (htab->entries); + free (htab); +} + +/* This function clears all entries in the given hash table. */ + +void +empty_hash_table (htab) + hash_table_t htab; +{ + memset (htab->entries, 0, htab->size * sizeof (hash_table_entry_t)); +} + +/* 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. */ + +static void +expand_hash_table (htab) + hash_table_t htab; +{ + hash_table_t new_htab; + hash_table_entry_t *entry_ptr; + hash_table_entry_t *new_entry_ptr; + + new_htab = create_hash_table (htab->number_of_elements * 2, + htab->hash_function, htab->eq_function); + for (entry_ptr = htab->entries; entry_ptr < htab->entries + htab->size; + entry_ptr++) + if (*entry_ptr != EMPTY_ENTRY && *entry_ptr != DELETED_ENTRY) + { + new_entry_ptr = find_hash_table_entry (new_htab, *entry_ptr, 1); + *new_entry_ptr = (*entry_ptr); + } + free (htab->entries); + *htab = (*new_htab); + free (new_htab); +} + +/* This function searches for hash table entry which contains element + equal to given value or empty entry in which given value can be + placed (if the element with given value does not exist in the + table). The function works in two regimes. The first regime is + used only for search. The second is used for search and + reservation empty entry for given value. The table is expanded if + occupancy (taking into accout also deleted elements) is more than + 75%. Naturally the hash table must already exist. If reservation + flag is TRUE then the element with given value should be inserted + into the table entry before another call of + `find_hash_table_entry'. */ + +hash_table_entry_t * +find_hash_table_entry (htab, element, reserve) + hash_table_t htab; + hash_table_entry_t element; + int reserve; +{ + hash_table_entry_t *entry_ptr; + hash_table_entry_t *first_deleted_entry_ptr; + unsigned index, hash_value, secondary_hash_value; + + if (htab->size * 3 <= htab->number_of_elements * 4) + { + all_expansions++; + expand_hash_table (htab); + } + hash_value = (*htab->hash_function) (element); + secondary_hash_value = 1 + hash_value % (htab->size - 2); + index = hash_value % htab->size; + htab->searches++; + all_searches++; + first_deleted_entry_ptr = NULL; + for (;;htab->collisions++, all_collisions++) + { + entry_ptr = htab->entries + index; + if (*entry_ptr == EMPTY_ENTRY) + { + if (reserve) + { + htab->number_of_elements++; + if (first_deleted_entry_ptr != NULL) + { + entry_ptr = first_deleted_entry_ptr; + *entry_ptr = EMPTY_ENTRY; + } + } + break; + } + else if (*entry_ptr != DELETED_ENTRY) + { + if ((*htab->eq_function) (*entry_ptr, element)) + break; + } + else if (first_deleted_entry_ptr == NULL) + first_deleted_entry_ptr = entry_ptr; + index += secondary_hash_value; + if (index >= htab->size) + index -= htab->size; + } + return entry_ptr; +} + +/* This function deletes element with given value from hash table. + The hash table entry value will be `DELETED_ENTRY' after the + function call. Naturally the hash table must already exist. Hash + table entry for given value should be not empty (or deleted). */ + +void +remove_element_from_hash_table_entry (htab, element) + hash_table_t htab; + hash_table_entry_t element; +{ + hash_table_entry_t *entry_ptr; + + entry_ptr = find_hash_table_entry (htab, element, 0); + *entry_ptr = DELETED_ENTRY; + htab->number_of_deleted_elements++; +} + +/* 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 +clear_hash_table_slot (htab, slot) + hash_table_t htab; + hash_table_entry_t *slot; +{ + if (slot < htab->entries || slot >= htab->entries + htab->size + || *slot == EMPTY_ENTRY || *slot == DELETED_ENTRY) + abort (); + *slot = DELETED_ENTRY; + htab->number_of_deleted_elements++; +} + +/* 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 +traverse_hash_table (htab, callback, info) + hash_table_t htab; + int (*callback) PARAMS ((hash_table_entry_t, void *)); + void *info; +{ + hash_table_entry_t *entry_ptr; + for (entry_ptr = htab->entries; entry_ptr < htab->entries + htab->size; + entry_ptr++) + if (*entry_ptr != EMPTY_ENTRY && *entry_ptr != DELETED_ENTRY) + if (!callback (*entry_ptr, info)) + break; +} + +/* The following function returns current size of given hash table. */ + +size_t +hash_table_size (htab) + hash_table_t htab; +{ + return htab->size; +} + +/* The following function returns current number of elements in given + hash table. */ + +size_t +hash_table_elements_number (htab) + hash_table_t htab; +{ + return htab->number_of_elements - htab->number_of_deleted_elements; +} + +/* The following function returns number of percents of fixed + collisions during all work with given hash table. */ + +int +hash_table_collisions (htab) + hash_table_t htab; +{ + int searches; + + searches = htab->searches; + if (searches == 0) + searches++; + return htab->collisions * 100 / searches; +} + +/* The following function returns number of percents of fixed + collisions during all work with all hash tables. */ + +int +all_hash_table_collisions () +{ + int searches; + + searches = all_searches; + if (searches == 0) + searches++; + return all_collisions * 100 / searches; +} |