usr/src/common/util/bsearch.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 /*      Copyright (c) 1988 AT&T */
  28 /*        All Rights Reserved   */
  29
  30 /*
  31  * Binary search algorithm, generalized from Knuth (6.2.1) Algorithm B.
  32  */
  33
  34 #if !defined(_BOOT) && !defined(_KMDB)
  35 #include "lint.h"
  36 #endif /* !_BOOT && !_KMDB */
  37 #include <stddef.h>
  38 #include <stdlib.h>
  39 #include <sys/types.h>
  40
  41 void *
  42 bsearch(const void *ky,         /* Key to be located */
  43         const void *bs,         /* Beginning of table */
  44         size_t nel,             /* Number of elements in the table */
  45         size_t width,           /* Width of an element (bytes) */
  46         int (*compar)(const void *, const void *)) /* Comparison function */
  47 {
  48         char *base;
  49         size_t two_width;
  50         char *last;             /* Last element in table */
  51
  52         if (nel == 0)
  53                 return (NULL);
  54
  55         base = (char *)bs;
  56         two_width = width + width;
  57         last = base + width * (nel - 1);
  58
  59         while (last >= base) {
  60
  61                 char *p = base + width * ((last - base)/two_width);
  62                 int res = (*compar)(ky, (void *)p);
  63
  64                 if (res == 0)
  65                         return (p);     /* Key found */
  66                 if (res < 0)
  67                         last = p - width;
  68                 else
  69                         base = p + width;
  70         }
  71         return (NULL);          /* Key not found */
  72 }