1 /* 2 * Copyright (c) 1990 Regents of the University of California. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. [rescinded 22 July 1999] 14 * 4. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 */ 30 31 /* 32 33 @deftypefn Supplemental void* bsearch (const void *@var{key}, @ 34 const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @ 35 int (*@var{compar})(const void *, const void *)) 36 37 Performs a search over an array of @var{nmemb} elements pointed to by 38 @var{base} for a member that matches the object pointed to by @var{key}. 39 The size of each member is specified by @var{size}. The array contents 40 should be sorted in ascending order according to the @var{compar} 41 comparison function. This routine should take two arguments pointing to 42 the @var{key} and to an array member, in that order, and should return an 43 integer less than, equal to, or greater than zero if the @var{key} object 44 is respectively less than, matching, or greater than the array member. 45 46 @end deftypefn 47 48 */ 49 50 #include "config.h" 51 #include "ansidecl.h" 52 #include <sys/types.h> /* size_t */ 53 #include <stdio.h> 54 55 /* 56 * Perform a binary search. 57 * 58 * The code below is a bit sneaky. After a comparison fails, we 59 * divide the work in half by moving either left or right. If lim 60 * is odd, moving left simply involves halving lim: e.g., when lim 61 * is 5 we look at item 2, so we change lim to 2 so that we will 62 * look at items 0 & 1. If lim is even, the same applies. If lim 63 * is odd, moving right again involes halving lim, this time moving 64 * the base up one item past p: e.g., when lim is 5 we change base 65 * to item 3 and make lim 2 so that we will look at items 3 and 4. 66 * If lim is even, however, we have to shrink it by one before 67 * halving: e.g., when lim is 4, we still looked at item 2, so we 68 * have to make lim 3, then halve, obtaining 1, so that we will only 69 * look at item 3. 70 */ 71 void * 72 bsearch (register const void *key, const void *base0, 73 size_t nmemb, register size_t size, 74 register int (*compar)(const void *, const void *)) 75 { 76 register const char *base = (const char *) base0; 77 register int lim, cmp; 78 register const void *p; 79 80 for (lim = nmemb; lim != 0; lim >>= 1) { 81 p = base + (lim >> 1) * size; 82 cmp = (*compar)(key, p); 83 if (cmp == 0) 84 return (void *)p; 85 if (cmp > 0) { /* key > p: move right */ 86 base = (const char *)p + size; 87 lim--; 88 } /* else move left */ 89 } 90 return (NULL); 91 } 92
