LXR linux/include/linux/count

   1/* Count leading and trailing zeros functions
   2 *
   3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public Licence
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the Licence, or (at your option) any later version.
  10 */
  11
  12#ifndef _LINUX_BITOPS_COUNT_ZEROS_H_
  13#define _LINUX_BITOPS_COUNT_ZEROS_H_
  14
  15#include <asm/bitops.h>
  16
  17/**
  18 * count_leading_zeros - Count the number of zeros from the MSB back
  19 * @x: The value
  20 *
  21 * Count the number of leading zeros from the MSB going towards the LSB in @x.
  22 *
  23 * If the MSB of @x is set, the result is 0.
  24 * If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
  25 * If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
  26 */
  27static inline int count_leading_zeros(unsigned long x)
  28{
  29        if (sizeof(x) == 4)
  30                return BITS_PER_LONG - fls(x);
  31        else
  32                return BITS_PER_LONG - fls64(x);
  33}
  34
  35#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
  36
  37/**
  38 * count_trailing_zeros - Count the number of zeros from the LSB forwards
  39 * @x: The value
  40 *
  41 * Count the number of trailing zeros from the LSB going towards the MSB in @x.
  42 *
  43 * If the LSB of @x is set, the result is 0.
  44 * If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
  45 * If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
  46 */
  47static inline int count_trailing_zeros(unsigned long x)
  48{
  49#define COUNT_TRAILING_ZEROS_0 (-1)
  50
  51        if (sizeof(x) == 4)
  52                return ffs(x);
  53        else
  54                return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
  55}
  56
  57#endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */
  58