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/* findkey.c - The routine that finds a key entry in the file. */
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/* This file is part of GDBM, the GNU data base manager, by Philip A. Nelson.
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Copyright (C) 1990, 1991, 1993 Free Software Foundation, Inc.
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GDBM is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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GDBM is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GDBM; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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You may contact the author by:
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e-mail: phil@cs.wwu.edu
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us-mail: Philip A. Nelson
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Computer Science Department
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Western Washington University
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*************************************************************************/
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/* include system configuration before all else. */
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/* Read the data found in bucket entry ELEM_LOC in file DBF and
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return a pointer to it. Also, cache the read value. */
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_gdbm_read_entry (dbf, elem_loc)
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int num_bytes; /* For seeking and reading. */
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data_cache_elem *data_ca;
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/* Is it already in the cache? */
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if (dbf->cache_entry->ca_data.elem_loc == elem_loc)
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return dbf->cache_entry->ca_data.dptr;
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/* Set sizes and pointers. */
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key_size = dbf->bucket->h_table[elem_loc].key_size;
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data_size = dbf->bucket->h_table[elem_loc].data_size;
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data_ca = &dbf->cache_entry->ca_data;
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/* Set up the cache. */
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if (data_ca->dptr != NULL) free (data_ca->dptr);
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data_ca->key_size = key_size;
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data_ca->data_size = data_size;
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data_ca->elem_loc = elem_loc;
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data_ca->hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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if (key_size+data_size == 0)
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data_ca->dptr = (char *) malloc (1);
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data_ca->dptr = (char *) malloc (key_size+data_size);
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if (data_ca->dptr == NULL) _gdbm_fatal (dbf, "malloc error");
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/* Read into the cache. */
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file_pos = lseek (dbf->desc,
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dbf->bucket->h_table[elem_loc].data_pointer, L_SET);
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if (file_pos != dbf->bucket->h_table[elem_loc].data_pointer)
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_gdbm_fatal (dbf, "lseek error");
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num_bytes = read (dbf->desc, data_ca->dptr, key_size+data_size);
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if (num_bytes != key_size+data_size) _gdbm_fatal (dbf, "read error");
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/* Find the KEY in the file and get ready to read the associated data. The
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return value is the location in the current hash bucket of the KEY's
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entry. If it is found, a pointer to the data and the key are returned
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in DPTR. If it is not found, the value -1 is returned. Since find
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key computes the hash value of key, that value */
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_gdbm_findkey (dbf, key, dptr, new_hash_val)
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word_t *new_hash_val; /* The new hash value. */
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word_t bucket_hash_val; /* The hash value from the bucket. */
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char *file_key; /* The complete key as stored in the file. */
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int elem_loc; /* The location in the bucket. */
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int home_loc; /* The home location in the bucket. */
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int key_size; /* Size of the key on the file. */
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/* Compute hash value and load proper bucket. */
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*new_hash_val = _gdbm_hash (key);
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_gdbm_get_bucket (dbf, *new_hash_val>> (31-dbf->header->dir_bits));
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/* Is the element the last one found for this bucket? */
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if (dbf->cache_entry->ca_data.elem_loc != -1
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&& *new_hash_val == dbf->cache_entry->ca_data.hash_val
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&& dbf->cache_entry->ca_data.key_size == key.dsize
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&& dbf->cache_entry->ca_data.dptr != NULL
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&& bcmp (dbf->cache_entry->ca_data.dptr, key.dptr, key.dsize) == 0)
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/* This is it. Return the cache pointer. */
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*dptr = dbf->cache_entry->ca_data.dptr+key.dsize;
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return dbf->cache_entry->ca_data.elem_loc;
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/* It is not the cached value, search for element in the bucket. */
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elem_loc = *new_hash_val % dbf->header->bucket_elems;
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bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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while (bucket_hash_val != -1)
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key_size = dbf->bucket->h_table[elem_loc].key_size;
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if (bucket_hash_val != *new_hash_val
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|| key_size != key.dsize
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|| bcmp (dbf->bucket->h_table[elem_loc].key_start, key.dptr,
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(SMALL < key_size ? SMALL : key_size)) != 0)
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/* Current elem_loc is not the item, go to next item. */
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elem_loc = (elem_loc + 1) % dbf->header->bucket_elems;
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if (elem_loc == home_loc) return -1;
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bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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/* This may be the one we want.
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The only way to tell is to read it. */
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file_key = _gdbm_read_entry (dbf, elem_loc);
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if (bcmp (file_key, key.dptr, key_size) == 0)
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/* This is the item. */
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*dptr = file_key+key.dsize;
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/* Not the item, try the next one. Return if not found. */
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elem_loc = (elem_loc + 1) % dbf->header->bucket_elems;
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if (elem_loc == home_loc) return -1;
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bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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/* If we get here, we never found the key. */
added
removed
findkey.c
