LXR linux/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/export.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 */
  33void *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}
  53EXPORT_SYMBOL(bsearch);
  54