diff options
Diffstat (limited to 'lib/libc/db/btree/bt_search.c')
| -rw-r--r-- | lib/libc/db/btree/bt_search.c | 235 |
1 files changed, 235 insertions, 0 deletions
diff --git a/lib/libc/db/btree/bt_search.c b/lib/libc/db/btree/bt_search.c new file mode 100644 index 0000000..ff33421 --- /dev/null +++ b/lib/libc/db/btree/bt_search.c @@ -0,0 +1,235 @@ +/*- + * Copyright (c) 1990, 1993 + * 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 8.6 (Berkeley) 3/15/94"; +#endif /* LIBC_SCCS and not lint */ + +#include <sys/types.h> + +#include <stdio.h> + +#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, and duplicates aren't allowed, we're + * done. If duplicates are allowed, it's possible that there + * were duplicate keys on duplicate pages, and they were later + * deleted, so we could be on a page with no matches while + * there are matches on other pages. If we're at the start or + * end of a page, check on both sides. + */ + if (h->flags & P_BLEAF) { + t->bt_cur.index = base; + *exactp = 0; + if (!ISSET(t, B_NODUPS)) { + if (base == 0 && + bt_sprev(t, h, key, exactp)) + return (&t->bt_cur); + if (base == NEXTINDEX(h) && + bt_snext(t, h, key, exactp)) + return (&t->bt_cur); + } + 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: if (__bt_push(t, h->pgno, index) == RET_ERROR) + return (NULL); + 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 to search + * h: current page. + * key: key to find + * 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; + PAGE *tp; + pgno_t pg; + + /* Skip until reach the end of the tree or a key. */ + for (pg = h->nextpg; pg != P_INVALID;) { + if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) { + mpool_put(t->bt_mp, h, 0); + return (NULL); + } + if (NEXTINDEX(tp) != 0) + break; + pg = tp->prevpg; + mpool_put(t->bt_mp, tp, 0); + } + /* + * The key is either an exact match, or not as good as + * the one we already have. + */ + if (pg != P_INVALID) { + e.page = tp; + e.index = NEXTINDEX(tp) - 1; + if (__bt_cmp(t, key, &e) == 0) { + mpool_put(t->bt_mp, h, 0); + t->bt_cur = e; + *exactp = 1; + return (1); + } + } + return (0); +} + +/* + * BT_SPREV -- Check for an exact match before the key. + * + * Parameters: + * t: tree to search + * h: current page. + * key: key to find + * 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; + PAGE *tp; + pgno_t pg; + + /* Skip until reach the beginning of the tree or a key. */ + for (pg = h->prevpg; pg != P_INVALID;) { + if ((tp = mpool_get(t->bt_mp, pg, 0)) == NULL) { + mpool_put(t->bt_mp, h, 0); + return (NULL); + } + if (NEXTINDEX(tp) != 0) + break; + pg = tp->prevpg; + mpool_put(t->bt_mp, tp, 0); + } + /* + * The key is either an exact match, or not as good as + * the one we already have. + */ + if (pg != P_INVALID) { + e.page = tp; + e.index = NEXTINDEX(tp) - 1; + if (__bt_cmp(t, key, &e) == 0) { + mpool_put(t->bt_mp, h, 0); + t->bt_cur = e; + *exactp = 1; + return (1); + } + } + return (0); +} |
