Net2/usr/src/lib/libc/db/btree/search.c
/*-
* Copyright (c) 1990 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[] = "@(#)search.c 5.2 (Berkeley) 4/8/91";
#endif /* LIBC_SCCS and not lint */
#include <sys/types.h>
#include <db.h>
#include "btree.h"
/*
* _BT_FIRST -- Find the first item in the tree that matches the supplied
* key.
*
* This routine supports deletion. When the user supplies a key to
* be deleted, we find the first one, and iteratively delete all the
* matching ones that follow it.
*
* Parameters:
* t -- btree in which to find first occurrence
* key -- key to find
*
* Returns:
* The BTITEM for the matching item. If there's no match,
* this may point to the first item > than the supplied key,
* or off the end of the page.
*
* Warnings:
* The BTITEM returned is in static space and will be overwritten
* by the next search of any kind in any btree.
*/
BTITEM *
_bt_first(t, key)
BTREE_P t;
DBT *key;
{
BTHEADER *h;
BTITEM *item;
index_t next;
int r;
/* find any matching item */
item = _bt_search(t, key);
h = t->bt_curpage;
next = NEXTINDEX(h);
/* if we're off the end of the page, search failed and we're done */
if (item->bti_index >= next)
return (item);
/* as long as we have an exact match, walk backwards */
while ((r = _bt_cmp(t, key->data, item->bti_index)) == 0) {
/* at start of page? */
if (item->bti_index == 0) {
/* if no prev page, we're done */
if (h->h_prevpg == P_NONE)
return (item);
/* walk backward, skipping empty pages */
do {
if (_bt_getpage(t, h->h_prevpg) == RET_ERROR)
return ((BTITEM *) NULL);
h = t->bt_curpage;
} while (NEXTINDEX(h) == 0 && h->h_prevpg != P_NONE);
if (NEXTINDEX(h) != 0)
item->bti_index = NEXTINDEX(h) - 1;
else
item->bti_index = 0;
item->bti_pgno = h->h_pgno;
} else {
item->bti_index--;
}
}
/* if we went too far backwards, step forward one entry */
if (r > 0) {
if (++(item->bti_index) >= NEXTINDEX(h)
&& h->h_nextpg != P_NONE) {
/* walk forward, skipping empty pages */
do {
if (_bt_getpage(t, h->h_nextpg) == RET_ERROR)
return ((BTITEM *) NULL);
h = t->bt_curpage;
} while (h->h_nextpg != P_NONE && NEXTINDEX(h) == 0);
item->bti_index = 0;
item->bti_pgno = h->h_pgno;
}
}
/* got it */
return (item);
}
/*
* _BT_SEARCH, _BT_SEARCHR -- Search for a particular key in the tree.
*
* Parameters:
* t -- btree in which to search
* key -- key to find
*
* Returns:
* BTITEM for matching item, if any, or the BTITEM for the
* location of the key, if it were in the tree.
*
* Warnings:
* The BTITEM returned is in static memory, and will be
* overwritten by the next search of any kind in any tree.
*/
BTITEM *
_bt_search(t, key)
BTREE_P t;
DBT *key;
{
/* we want to start all of our searches at the root */
if (_bt_getpage(t, (pgno_t) P_ROOT) == RET_ERROR)
return ((BTITEM *) NULL);
return (_bt_searchr(t, key));
}
BTITEM *
_bt_searchr(t, key)
BTREE_P t;
DBT *key;
{
BTHEADER *h = t->bt_curpage;
index_t index;
IDATUM *id;
DATUM *d;
static BTITEM item;
/* do a binary search on the current page */
index = _bt_binsrch(t, key->data);
/*
* At this point, the binary search terminated because the endpoints
* got too close together, or we have a match. Figure out which
* case applies and decide what to do based on the page type.
*/
if (h->h_flags & F_LEAF) {
item.bti_pgno = h->h_pgno;
item.bti_index = index;
if (index < NEXTINDEX(h))
d = (DATUM *) GETDATUM(h,index);
else
d = (DATUM *) NULL;
item.bti_datum = d;
return(&item);
} else {
id = (IDATUM *) GETDATUM(h, index);
if (_bt_push(t, h->h_pgno) == RET_ERROR)
return ((BTITEM *) NULL);
if (_bt_getpage(t, id->i_pgno) == RET_ERROR)
return ((BTITEM *) NULL);
return (_bt_searchr(t, key));
}
}
/*
* _BT_BINSRCH -- Do a binary search for a given key on the current page.
*
* Searches on internal pages are handled slightly differently from
* searches on leaf pages. This is because internal page searches
* find the largest item <= key in the tree, and leaf searches find
* the smallest item >= key. This guarantees that leaf page searches
* leave us pointing at the item's correct position, and internal
* searches descend the tree correctly.
*
* Parameters:
* t -- tree to search
* key -- key we're looking for
*
* Returns:
* Index of the line pointer array entry for the (closest)
* match to key on the current page, with "closest" as defined
* above.
*/
index_t
_bt_binsrch(t, key)
BTREE_P t;
char *key;
{
index_t lbound, ubound, cur;
BTHEADER *h = t->bt_curpage;
int match = 0;
int r;
lbound = 0;
ubound = NEXTINDEX(h);
if (ubound > 0)
--ubound;
/* do a binary search on the current page */
while ((ubound - lbound) > 1) {
cur = lbound + ((ubound - lbound) / 2);
r = _bt_cmp(t, key, cur);
if (r > 0)
lbound = cur + 1;
else if (r < 0)
ubound = cur;
else {
match++;
break;
}
}
/*
* At this point, the binary search terminated because the endpoints
* got too close together, or we have a match. Figure out which
* case applies, decide what to do based on the page type (leaf or
* internal), and do the right thing.
*/
if (match) {
return (cur);
} else if (ubound != lbound) {
if (h->h_flags & F_LEAF) {
r = _bt_cmp(t, key, lbound);
if (r <= 0) {
return (lbound);
}
} else {
r = _bt_cmp(t, key, ubound);
/* for internal nodes, move as far left as possible */
if (r < 0) {
r = _bt_cmp(t, key, lbound);
if (r < 0 && lbound > 0)
--lbound;
return (lbound);
} else {
return (ubound);
}
}
}
if (h->h_flags & F_LEAF) {
if (ubound < NEXTINDEX(h)) {
r = _bt_cmp(t, key, ubound);
if (r > 0)
ubound++;
}
} else {
/* for internal pages, move as far left as possible */
if (ubound == NEXTINDEX(h))
ubound--;
while (_bt_cmp(t, key, ubound) < 0)
ubound--;
}
return (ubound);
}