1 /** @file 2 Binary search utility function. 3 4 This utility makes use of a comparison function to search arrays of 5 unspecified type. Where an argument declared as size_t nmemb specifies the 6 length of the array for a function, nmemb can have the value zero on a call 7 to that function; the comparison function is not called, a search finds no 8 matching element. Pointer arguments on such a call shall still have valid 9 values. 10 11 The implementation shall ensure that the second argument of the comparison 12 function is a pointer to an element of the array. The first argument shall 13 equal key. 14 15 The comparison function shall not alter the contents of the array. The 16 implementation may reorder elements of the array between calls to the 17 comparison function, but shall not alter the contents of any individual 18 element. 19 20 When the same objects (consisting of size bytes, irrespective of their 21 current positions in the array) are passed more than once to the comparison 22 function, the results shall be consistent with one another. That is, the same 23 object shall always compare the same way with the key. 24 25 A sequence point occurs immediately before and immediately after each call to 26 the comparison function, and also between any call to the comparison function 27 and any movement of the objects passed as arguments to that call. 28 29 Copyright (c) 2010, Intel Corporation. All rights reserved.<BR> 30 31 * Copyright (c) 1990, 1993 32 * The Regents of the University of California. All rights reserved. 33 * 34 * Redistribution and use in source and binary forms, with or without 35 * modification, are permitted provided that the following conditions 36 * are met: 37 * 1. Redistributions of source code must retain the above copyright 38 * notice, this list of conditions and the following disclaimer. 39 * 2. Redistributions in binary form must reproduce the above copyright 40 * notice, this list of conditions and the following disclaimer in the 41 * documentation and/or other materials provided with the distribution. 42 * 4. Neither the name of the University nor the names of its contributors 43 * may be used to endorse or promote products derived from this software 44 * without specific prior written permission. 45 * 46 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 47 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 48 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 49 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 50 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 51 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 52 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 53 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 54 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 55 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 56 * SUCH DAMAGE. 57 58 ("$FreeBSD: src/lib/libc/stdlib/bsearch.c,v 1.4.10.1.2.1 2009/10/25 01:10:29 kensmith Exp $"); 59 **/ 60 #include <LibConfig.h> 61 #include <sys/EfiCdefs.h> 62 #include <stdlib.h> 63 64 /* 65 * Perform a binary search. 66 * 67 * The code below is a bit sneaky. After a comparison fails, we 68 * divide the work in half by moving either left or right. If lim 69 * is odd, moving left simply involves halving lim: e.g., when lim 70 * is 5 we look at item 2, so we change lim to 2 so that we will 71 * look at items 0 & 1. If lim is even, the same applies. If lim 72 * is odd, moving right again involes halving lim, this time moving 73 * the base up one item past p: e.g., when lim is 5 we change base 74 * to item 3 and make lim 2 so that we will look at items 3 and 4. 75 * If lim is even, however, we have to shrink it by one before 76 * halving: e.g., when lim is 4, we still looked at item 2, so we 77 * have to make lim 3, then halve, obtaining 1, so that we will only 78 * look at item 3. 79 */ 80 void * 81 bsearch( 82 const void *key, 83 const void *base0, 84 size_t nmemb, 85 size_t size, 86 int (*compar)(const void *, const void *) 87 ) 88 { 89 const char *base = base0; 90 size_t lim; 91 int cmp; 92 const void *p; 93 94 for (lim = nmemb; lim != 0; lim >>= 1) { 95 p = base + (lim >> 1) * size; 96 cmp = (*compar)(key, p); 97 if (cmp == 0) 98 return ((void *)p); 99 if (cmp > 0) { /* key > p: move right */ 100 base = (char *)p + size; 101 lim--; 102 } /* else move left */ 103 } 104 return (NULL); 105 } 106
