linux-stable/include/linux/count_zeros.h

/* 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_ */