include/linux/count_zeros.h

   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  */
  27 static 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  */
  47 static 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_ */