1 /*- 2 * Copyright (c) 1990 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Mike Olson. 7 * 8 * %sccs.include.redist.c% 9 */ 10 11 #if defined(LIBC_SCCS) && !defined(lint) 12 static char sccsid[] = "@(#)bt_search.c 5.5 (Berkeley) 11/13/92"; 13 #endif /* LIBC_SCCS and not lint */ 14 15 #include <sys/types.h> 16 17 #include <db.h> 18 #include <stdio.h> 19 20 #include "btree.h" 21 22 /* 23 * __BT_SEARCH -- Search a btree for a key. 24 * 25 * Parameters: 26 * t: tree to search 27 * key: key to find 28 * exactp: pointer to exact match flag 29 * 30 * Returns: 31 * EPG for matching record, if any, or the EPG for the location of the 32 * key, if it were inserted into the tree. 33 * 34 * Warnings: 35 * The EPG returned is in static memory, and will be overwritten by the 36 * next search of any kind in any tree. 37 */ 38 EPG * 39 __bt_search(t, key, exactp) 40 BTREE *t; 41 const DBT *key; 42 int *exactp; 43 { 44 register index_t index; 45 register int base, cmp, lim; 46 register PAGE *h; 47 pgno_t pg; 48 static EPG e; 49 50 for (pg = P_ROOT;;) { 51 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 52 return (NULL); 53 54 /* Do a binary search on the current page. */ 55 e.page = h; 56 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 57 e.index = index = base + (lim >> 1); 58 if ((cmp = __bt_cmp(t, key, &e)) == 0) { 59 if (h->flags & P_BLEAF) { 60 *exactp = 1; 61 return (&e); 62 } 63 goto next; 64 } 65 if (cmp > 0) { 66 base = index + 1; 67 --lim; 68 } 69 } 70 71 /* 72 * No match found. Base is the smallest index greater than 73 * key but may be an illegal index. Use base if it's a leaf 74 * page, decrement it by one if it's an internal page. This 75 * is safe because internal pages can't be empty. 76 */ 77 index = h->flags & P_BLEAF ? base : base - 1; 78 79 /* If it's a leaf page, we're done. */ 80 if (h->flags & P_BLEAF) { 81 e.index = index; 82 *exactp = 0; 83 return (&e); 84 } 85 86 next: if (__bt_push(t, h->pgno, index) == RET_ERROR) 87 return (NULL); 88 pg = GETBINTERNAL(h, index)->pgno; 89 mpool_put(t->bt_mp, h, 0); 90 } 91 } 92