include/linux/count_zeros.h

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /* Count leading and trailing zeros functions
   3  *
   4  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #ifndef _LINUX_BITOPS_COUNT_ZEROS_H_
   9 #define _LINUX_BITOPS_COUNT_ZEROS_H_
  10
  11 #include <asm/bitops.h>
  12
  13 /**
  14  * count_leading_zeros - Count the number of zeros from the MSB back
  15  * @x: The value
  16  *
  17  * Count the number of leading zeros from the MSB going towards the LSB in @x.
  18  *
  19  * If the MSB of @x is set, the result is 0.
  20  * If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
  21  * If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
  22  */
  23 static inline int count_leading_zeros(unsigned long x)
  24 {
  25         if (sizeof(x) == 4)
  26                 return BITS_PER_LONG - fls(x);
  27         else
  28                 return BITS_PER_LONG - fls64(x);
  29 }
  30
  31 #define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
  32
  33 /**
  34  * count_trailing_zeros - Count the number of zeros from the LSB forwards
  35  * @x: The value
  36  *
  37  * Count the number of trailing zeros from the LSB going towards the MSB in @x.
  38  *
  39  * If the LSB of @x is set, the result is 0.
  40  * If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
  41  * If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
  42  */
  43 static inline int count_trailing_zeros(unsigned long x)
  44 {
  45 #define COUNT_TRAILING_ZEROS_0 (-1)
  46
  47         if (sizeof(x) == 4)
  48                 return ffs(x);
  49         else
  50                 return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
  51 }
  52
  53 #endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */