IABSD.fr/src/lib/libc/stdlib/bsearch.c

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• Author : cheloha
  Date : 2021-12-02 20:58:01
  Hash : d10db4f7
  Message : bsearch(3): support arrays with more than INT_MAX elements The "lim" variable needs to be a size_t to match nmemb, otherwise we get undefined behavior when nmemb exceeds INT_MAX. Prompted by a blog post by Joshua Bloch: https://ai.googleblog.com/2006/06/extra-extra-read-all-about-it-nearly.html Fixed by Chris Torek a long time ago: https://svnweb.freebsd.org/csrg/lib/libc/stdlib/bsearch.c?revision=51742&view=markup ok millert@

• lib/libc/stdlib/bsearch.c

• /*	$OpenBSD: bsearch.c,v 1.9 2021/12/02 20:58:01 cheloha Exp $ */
  /*
   * Copyright (c) 1990 Regents of the University of California.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  #include <stdlib.h>
  
  /*
   * Perform a binary search.
   *
   * The code below is a bit sneaky.  After a comparison fails, we
   * divide the work in half by moving either left or right. If lim
   * is odd, moving left simply involves halving lim: e.g., when lim
   * is 5 we look at item 2, so we change lim to 2 so that we will
   * look at items 0 & 1.  If lim is even, the same applies.  If lim
   * is odd, moving right again involves halving lim, this time moving
   * the base up one item past p: e.g., when lim is 5 we change base
   * to item 3 and make lim 2 so that we will look at items 3 and 4.
   * If lim is even, however, we have to shrink it by one before
   * halving: e.g., when lim is 4, we still looked at item 2, so we
   * have to make lim 3, then halve, obtaining 1, so that we will only
   * look at item 3.
   */
  void *
  bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
      int (*compar)(const void *, const void *))
  {
  	const char *base = base0;
  	const void *p;
  	size_t lim;
  	int cmp;
  
  	for (lim = nmemb; lim != 0; lim >>= 1) {
  		p = base + (lim >> 1) * size;
  		cmp = (*compar)(key, p);
  		if (cmp == 0)
  			return ((void *)p);
  		if (cmp > 0) {	/* key > p: move right */
  			base = (char *)p + size;
  			lim--;
  		} /* else move left */
  	}
  	return (NULL);
  }