Branch data     Line data    Source code

       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                 :          3 :                 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_ */