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+/* 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;
+}