count_zeros.h
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/* Count leading and trailing zeros functions
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#ifndef _LINUX_BITOPS_COUNT_ZEROS_H_
#define _LINUX_BITOPS_COUNT_ZEROS_H_
#include <asm/bitops.h>
/**
* count_leading_zeros - Count the number of zeros from the MSB back
* @x: The value
*
* Count the number of leading zeros from the MSB going towards the LSB in @x.
*
* If the MSB of @x is set, the result is 0.
* If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
* If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
*/
static inline int count_leading_zeros(unsigned long x)
{
if (sizeof(x) == 4)
return BITS_PER_LONG - fls(x);
else
return BITS_PER_LONG - fls64(x);
}
#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
/**
* count_trailing_zeros - Count the number of zeros from the LSB forwards
* @x: The value
*
* Count the number of trailing zeros from the LSB going towards the MSB in @x.
*
* If the LSB of @x is set, the result is 0.
* If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
* If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
*/
static inline int count_trailing_zeros(unsigned long x)
{
#define COUNT_TRAILING_ZEROS_0 (-1)
if (sizeof(x) == 4)
return ffs(x);
else
return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
}
#endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */