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 5.9 (Berkeley) 02/14/93"; 13 #endif /* LIBC_SCCS and not lint */ 14 15 #include <sys/types.h> 16 17 #include <stdio.h> 18 19 #include <db.h> 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 indx_t index; 45 register int base, cmp, lim; 46 register PAGE *h; 47 pgno_t pg; 48 static EPG e; 49 50 BT_CLR(t); 51 for (pg = P_ROOT;;) { 52 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 53 return (NULL); 54 55 /* Do a binary search on the current page. */ 56 e.page = h; 57 for (base = 0, lim = NEXTINDEX(h); lim; lim >>= 1) { 58 e.index = index = base + (lim >> 1); 59 if ((cmp = __bt_cmp(t, key, &e)) == 0) { 60 if (h->flags & P_BLEAF) { 61 *exactp = 1; 62 return (&e); 63 } 64 goto next; 65 } 66 if (cmp > 0) { 67 base = index + 1; 68 --lim; 69 } 70 } 71 72 /* If it's a leaf page, we're done. */ 73 if (h->flags & P_BLEAF) { 74 e.index = base; 75 *exactp = 0; 76 return (&e); 77 } 78 79 /* 80 * No match found. Base is the smallest index greater than 81 * key and may be zero or a last + 1 index. If it's non-zero, 82 * decrement by one, and record the internal page which should 83 * be a parent page for the key. If a split later occurs, the 84 * inserted page will be to the right of the saved page. 85 */ 86 index = base ? base - 1 : base; 87 88 next: if (__bt_push(t, h->pgno, index) == RET_ERROR) 89 return (NULL); 90 pg = GETBINTERNAL(h, index)->pgno; 91 mpool_put(t->bt_mp, h, 0); 92 } 93 } 94