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 */
27static 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 */
47static 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_ */
58