lib/bsearch.c

   1 /*
   2  * A generic implementation of binary search for the Linux kernel
   3  *
   4  * Copyright (C) 2008-2009 Ksplice, Inc.
   5  * Author: Tim Abbott <tabbott@ksplice.com>
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License as
   9  * published by the Free Software Foundation; version 2.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/bsearch.h>
  14
  15 /*
  16  * bsearch - binary search an array of elements
  17  * @key: pointer to item being searched for
  18  * @base: pointer to first element to search
  19  * @num: number of elements
  20  * @size: size of each element
  21  * @cmp: pointer to comparison function
  22  *
  23  * This function does a binary search on the given array.  The
  24  * contents of the array should already be in ascending sorted order
  25  * under the provided comparison function.
  26  *
  27  * Note that the key need not have the same type as the elements in
  28  * the array, e.g. key could be a string and the comparison function
  29  * could compare the string with the struct's name field.  However, if
  30  * the key and elements in the array are of the same type, you can use
  31  * the same comparison function for both sort() and bsearch().
  32  */
  33 void *bsearch(const void *key, const void *base, size_t num, size_t size,
  34               int (*cmp)(const void *key, const void *elt))
  35 {
  36         size_t start = 0, end = num;
  37         int result;
  38
  39         while (start < end) {
  40                 size_t mid = start + (end - start) / 2;
  41
  42                 result = cmp(key, base + mid * size);
  43                 if (result < 0)
  44                         end = mid;
  45                 else if (result > 0)
  46                         start = mid + 1;
  47                 else
  48                         return (void *)base + mid * size;
  49         }
  50
  51         return NULL;
  52 }
  53 EXPORT_SYMBOL(bsearch);