bt_search.c

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/*-
 * Copyright (c) 1990, 1993, 1994
 * The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Olson.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bt_search.c   8.8 (Berkeley) 7/31/94";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <stdio.h>

#include "../include/db.h"
#include "btree.h"

static int __bt_snext __P((BTREE *, PAGE *, const DBT *, int *));
static int __bt_sprev __P((BTREE *, PAGE *, const DBT *, int *));

/*
 * __bt_search --
 * Search a btree for a key.
 *
 * Parameters:
 * t: tree to search
 * key:  key to find
 * exactp:  pointer to exact match flag
 *
 * Returns:
 * The EPG for matching record, if any, or the EPG for the location
 * of the key, if it were inserted into the tree, is entered into
 * the bt_cur field of the tree.  A pointer to the field is returned.
 */
EPG *
__bt_search(t, key, exactp)
   BTREE *t;
   const DBT *key;
   int *exactp;
{
   PAGE *h;
   indx_t base, index, lim;
   pgno_t pg;
   int cmp;

   BT_CLR(t);
   for (pg = P_ROOT;;) {
      if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
         return (NULL);

      /* Do a binary search on the current page. */
      t->bt_cur.page = h;
      for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) {
         t->bt_cur.index = index = base + (lim >> 1);
         if ((cmp = __bt_cmp(t, key, &t->bt_cur)) == 0) {
            if (h->flags & P_BLEAF) {
               *exactp = 1;
               return (&t->bt_cur);
            }
            goto next;
         }
         if (cmp > 0) {
            base = index + 1;
            --lim;
         }
      }

      /*
       * If it's a leaf page, we're almost done.  If no duplicates
       * are allowed, or we have an exact match, we're done.  Else,
       * it's possible that there were matching keys on this page,
       * which later deleted, and we're on a page with no matches
       * while there are matches on other pages.  If at the start or
       * end of a page, check the adjacent page.
       */
      if (h->flags & P_BLEAF) {
         if (!F_ISSET(t, B_NODUPS)) {
            if (base == 0 &&
                h->prevpg != P_INVALID &&
                __bt_sprev(t, h, key, exactp))
               return (&t->bt_cur);
            if (base == NEXTINDEX(h) &&
                h->nextpg != P_INVALID &&
                __bt_snext(t, h, key, exactp))
               return (&t->bt_cur);
         }
         *exactp = 0;
         t->bt_cur.index = base;
         return (&t->bt_cur);
      }

      /*
       * No match found.  Base is the smallest index greater than
       * key and may be zero or a last + 1 index.  If it's non-zero,
       * decrement by one, and record the internal page which should
       * be a parent page for the key.  If a split later occurs, the
       * inserted page will be to the right of the saved page.
       */
      index = base ? base - 1 : base;

next:    BT_PUSH(t, h->pgno, index);
      pg = GETBINTERNAL(h, index)->pgno;
      mpool_put(t->bt_mp, h, 0);
   }
}

/*
 * __bt_snext --
 * Check for an exact match after the key.
 *
 * Parameters:
 * t: tree
 * h: current page
 * key:  key
 * exactp:  pointer to exact match flag
 *
 * Returns:
 * If an exact match found.
 */
static int
__bt_snext(t, h, key, exactp)
   BTREE *t;
   PAGE *h;
   const DBT *key;
   int *exactp;
{
   EPG e;

   /*
    * Get the next page.  The key is either an exact
    * match, or not as good as the one we already have.
    */
   if ((e.page = mpool_get(t->bt_mp, h->nextpg, 0)) == NULL)
      return (0);
   e.index = 0;
   if (__bt_cmp(t, key, &e) == 0) {
      mpool_put(t->bt_mp, h, 0);
      t->bt_cur = e;
      *exactp = 1;
      return (1);
   }
   mpool_put(t->bt_mp, e.page, 0);
   return (0);
}

/*
 * __bt_sprev --
 * Check for an exact match before the key.
 *
 * Parameters:
 * t: tree
 * h: current page
 * key:  key
 * exactp:  pointer to exact match flag
 *
 * Returns:
 * If an exact match found.
 */
static int
__bt_sprev(t, h, key, exactp)
   BTREE *t;
   PAGE *h;
   const DBT *key;
   int *exactp;
{
   EPG e;

   /*
    * Get the previous page.  The key is either an exact
    * match, or not as good as the one we already have.
    */
   if ((e.page = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL)
      return (0);
   e.index = NEXTINDEX(e.page) - 1;
   if (__bt_cmp(t, key, &e) == 0) {
      mpool_put(t->bt_mp, h, 0);
      t->bt_cur = e;
      *exactp = 1;
      return (1);
   }
   mpool_put(t->bt_mp, e.page, 0);
   return (0);
}