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Diffstat (limited to 'gnulib-local/lib/hash.c')
-rw-r--r-- | gnulib-local/lib/hash.c | 383 |
1 files changed, 383 insertions, 0 deletions
diff --git a/gnulib-local/lib/hash.c b/gnulib-local/lib/hash.c new file mode 100644 index 0000000..1844724 --- /dev/null +++ b/gnulib-local/lib/hash.c @@ -0,0 +1,383 @@ +/* hash - implement simple hashing table with string based keys. + Copyright (C) 1994-1995, 2000-2006 Free Software Foundation, Inc. + Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994. + + 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 3 of the License, 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, see <http://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* Specification. */ +#include "hash.h" + +#include <stdlib.h> +#include <string.h> +#include <stdio.h> +#include <limits.h> +#include <sys/types.h> + +/* Since this simple implementation of hash tables allows only insertion, no + removal of entries, the right data structure for the memory holding all keys + is an obstack. */ +#include "obstack.h" + +/* Use checked memory allocation. */ +#include "xalloc.h" + +#define obstack_chunk_alloc xmalloc +#define obstack_chunk_free free + + +typedef struct hash_entry +{ + unsigned long used; /* Hash code of the key, or 0 for an unused entry. */ + const void *key; /* Key. */ + size_t keylen; + void *data; /* Value. */ + struct hash_entry *next; +} +hash_entry; + + +/* Given an odd CANDIDATE > 1, return true if it is a prime number. */ +static int +is_prime (unsigned long int candidate) +{ + /* No even number and none less than 10 will be passed here. */ + unsigned long int divn = 3; + unsigned long int sq = divn * divn; + + while (sq < candidate && candidate % divn != 0) + { + ++divn; + sq += 4 * divn; + ++divn; + } + + return candidate % divn != 0; +} + + +/* Given SEED > 1, return the smallest odd prime number >= SEED. */ +unsigned long +next_prime (unsigned long int seed) +{ + /* Make it definitely odd. */ + seed |= 1; + + while (!is_prime (seed)) + seed += 2; + + return seed; +} + + +/* Initialize a hash table. INIT_SIZE > 1 is the initial number of available + entries. + Return 0 upon successful completion, -1 upon memory allocation error. */ +int +hash_init (hash_table *htab, unsigned long int init_size) +{ + /* We need the size to be a prime. */ + init_size = next_prime (init_size); + + /* Initialize the data structure. */ + htab->size = init_size; + htab->filled = 0; + htab->first = NULL; + htab->table = XCALLOC (init_size + 1, hash_entry); + + obstack_init (&htab->mem_pool); + + return 0; +} + + +/* Delete a hash table's contents. + Return 0 always. */ +int +hash_destroy (hash_table *htab) +{ + free (htab->table); + obstack_free (&htab->mem_pool, NULL); + return 0; +} + + +/* Compute a hash code for a key consisting of KEYLEN bytes starting at KEY + in memory. */ +static unsigned long +compute_hashval (const void *key, size_t keylen) +{ + size_t cnt; + unsigned long int hval; + + /* Compute the hash value for the given string. The algorithm + is taken from [Aho,Sethi,Ullman], fixed according to + http://www.haible.de/bruno/hashfunc.html. */ + cnt = 0; + hval = keylen; + while (cnt < keylen) + { + hval = (hval << 9) | (hval >> (sizeof (unsigned long) * CHAR_BIT - 9)); + hval += (unsigned long int) *(((const char *) key) + cnt++); + } + return hval != 0 ? hval : ~((unsigned long) 0); +} + + +/* References: + [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986 + [Knuth] The Art of Computer Programming, part3 (6.4) */ + +/* Look up a given key in the hash table. + Return the index of the entry, if present, or otherwise the index a free + entry where it could be inserted. */ +static size_t +lookup (hash_table *htab, + const void *key, size_t keylen, + unsigned long int hval) +{ + unsigned long int hash; + size_t idx; + hash_entry *table = htab->table; + + /* First hash function: simply take the modul but prevent zero. */ + hash = 1 + hval % htab->size; + + idx = hash; + + if (table[idx].used) + { + if (table[idx].used == hval && table[idx].keylen == keylen + && memcmp (table[idx].key, key, keylen) == 0) + return idx; + + /* Second hash function as suggested in [Knuth]. */ + hash = 1 + hval % (htab->size - 2); + + do + { + if (idx <= hash) + idx = htab->size + idx - hash; + else + idx -= hash; + + /* If entry is found use it. */ + if (table[idx].used == hval && table[idx].keylen == keylen + && memcmp (table[idx].key, key, keylen) == 0) + return idx; + } + while (table[idx].used); + } + return idx; +} + + +/* Look up the value of a key in the given table. + If found, return 0 and set *RESULT to it. Otherwise return -1. */ +int +hash_find_entry (hash_table *htab, const void *key, size_t keylen, + void **result) +{ + hash_entry *table = htab->table; + size_t idx = lookup (htab, key, keylen, compute_hashval (key, keylen)); + + if (table[idx].used == 0) + return -1; + + *result = table[idx].data; + return 0; +} + + +/* Insert the pair (KEY[0..KEYLEN-1], DATA) in the hash table at index IDX. + HVAL is the key's hash code. IDX depends on it. The table entry at index + IDX is known to be unused. */ +static void +insert_entry_2 (hash_table *htab, + const void *key, size_t keylen, + unsigned long int hval, size_t idx, void *data) +{ + hash_entry *table = htab->table; + + table[idx].used = hval; + table[idx].key = key; + table[idx].keylen = keylen; + table[idx].data = data; + + /* List the new value in the list. */ + if (htab->first == NULL) + { + table[idx].next = &table[idx]; + htab->first = &table[idx]; + } + else + { + table[idx].next = htab->first->next; + htab->first->next = &table[idx]; + htab->first = &table[idx]; + } + + ++htab->filled; +} + + +/* Grow the hash table. */ +static void +resize (hash_table *htab) +{ + unsigned long int old_size = htab->size; + hash_entry *table = htab->table; + size_t idx; + + htab->size = next_prime (htab->size * 2); + htab->filled = 0; + htab->first = NULL; + htab->table = XCALLOC (1 + htab->size, hash_entry); + + for (idx = 1; idx <= old_size; ++idx) + if (table[idx].used) + insert_entry_2 (htab, table[idx].key, table[idx].keylen, + table[idx].used, + lookup (htab, table[idx].key, table[idx].keylen, + table[idx].used), + table[idx].data); + + free (table); +} + + +/* Try to insert the pair (KEY[0..KEYLEN-1], DATA) in the hash table. + Return non-NULL (more precisely, the address of the KEY inside the table's + memory pool) if successful, or NULL if there is already an entry with the + given key. */ +const void * +hash_insert_entry (hash_table *htab, + const void *key, size_t keylen, + void *data) +{ + unsigned long int hval = compute_hashval (key, keylen); + hash_entry *table = htab->table; + size_t idx = lookup (htab, key, keylen, hval); + + if (table[idx].used) + /* We don't want to overwrite the old value. */ + return NULL; + else + { + /* An empty bucket has been found. */ + void *keycopy = obstack_copy (&htab->mem_pool, key, keylen); + insert_entry_2 (htab, keycopy, keylen, hval, idx, data); + if (100 * htab->filled > 75 * htab->size) + /* Table is filled more than 75%. Resize the table. */ + resize (htab); + return keycopy; + } +} + + +/* Insert the pair (KEY[0..KEYLEN-1], DATA) in the hash table. + Return 0. */ +int +hash_set_value (hash_table *htab, + const void *key, size_t keylen, + void *data) +{ + unsigned long int hval = compute_hashval (key, keylen); + hash_entry *table = htab->table; + size_t idx = lookup (htab, key, keylen, hval); + + if (table[idx].used) + { + /* Overwrite the old value. */ + table[idx].data = data; + return 0; + } + else + { + /* An empty bucket has been found. */ + void *keycopy = obstack_copy (&htab->mem_pool, key, keylen); + insert_entry_2 (htab, keycopy, keylen, hval, idx, data); + if (100 * htab->filled > 75 * htab->size) + /* Table is filled more than 75%. Resize the table. */ + resize (htab); + return 0; + } +} + + +/* Steps *PTR forward to the next used entry in the given hash table. *PTR + should be initially set to NULL. Store information about the next entry + in *KEY, *KEYLEN, *DATA. + Return 0 normally, -1 when the whole hash table has been traversed. */ +int +hash_iterate (hash_table *htab, void **ptr, const void **key, size_t *keylen, + void **data) +{ + hash_entry *curr; + + if (*ptr == NULL) + { + if (htab->first == NULL) + return -1; + curr = htab->first; + } + else + { + if (*ptr == htab->first) + return -1; + curr = (hash_entry *) *ptr; + } + curr = curr->next; + *ptr = (void *) curr; + + *key = curr->key; + *keylen = curr->keylen; + *data = curr->data; + return 0; +} + + +/* Steps *PTR forward to the next used entry in the given hash table. *PTR + should be initially set to NULL. Store information about the next entry + in *KEY, *KEYLEN, *DATAP. *DATAP is set to point to the storage of the + value; modifying **DATAP will modify the value of the entry. + Return 0 normally, -1 when the whole hash table has been traversed. */ +int +hash_iterate_modify (hash_table *htab, void **ptr, + const void **key, size_t *keylen, + void ***datap) +{ + hash_entry *curr; + + if (*ptr == NULL) + { + if (htab->first == NULL) + return -1; + curr = htab->first; + } + else + { + if (*ptr == htab->first) + return -1; + curr = (hash_entry *) *ptr; + } + curr = curr->next; + *ptr = (void *) curr; + + *key = curr->key; + *keylen = curr->keylen; + *datap = &curr->data; + return 0; +} |