usr/src/lib/libbc/libc/gen/common/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, Version 1.0 only
   6  * (the "License").  You may not use this file except in compliance
   7  * with the License.
   8  *
   9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  10  * or http://www.opensolaris.org/os/licensing.
  11  * See the License for the specific language governing permissions
  12  * and limitations under the License.
  13  *
  14  * When distributing Covered Code, include this CDDL HEADER in each
  15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  16  * If applicable, add the following below this CDDL HEADER, with the
  17  * fields enclosed by brackets "[]" replaced with your own identifying
  18  * information: Portions Copyright [yyyy] [name of copyright owner]
  19  *
  20  * CDDL HEADER END
  21  */
  22 /*      Copyright (c) 1984 AT&T */
  23 /*        All Rights Reserved   */
  24
  25 #pragma ident   "%Z%%M% %I%     %E% SMI"  /* from S5R2 1.5 */
  26
  27 /*LINTLIBRARY*/
  28 /*
  29  * Binary search algorithm, generalized from Knuth (6.2.1) Algorithm B.
  30  *
  31  */
  32
  33 typedef char *POINTER;
  34
  35 POINTER
  36 bsearch(key, base, nel, width, compar)
  37 POINTER key;                    /* Key to be located */
  38 POINTER base;                   /* Beginning of table */
  39 unsigned nel;                   /* Number of elements in the table */
  40 unsigned width;                 /* Width of an element (bytes) */
  41 int     (*compar)();            /* Comparison function */
  42 {
  43         int two_width = width + width;
  44         POINTER last = base + width * (nel - 1); /* Last element in table */
  45
  46         while (last >= base) {
  47
  48                 register POINTER p = base + width * ((last - base)/two_width);
  49                 register int res = (*compar)(key, p);
  50
  51                 if (res == 0)
  52                         return (p);     /* Key found */
  53                 if (res < 0)
  54                         last = p - width;
  55                 else
  56                         base = p + width;
  57         }
  58         return ((POINTER) 0);           /* Key not found */
  59 }