1 /* Count leading and trailing zeros functions
3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
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.
12 #ifndef _LINUX_BITOPS_COUNT_ZEROS_H_
13 #define _LINUX_BITOPS_COUNT_ZEROS_H_
15 #include <asm/bitops.h>
18 * count_leading_zeros - Count the number of zeros from the MSB back
21 * Count the number of leading zeros from the MSB going towards the LSB in @x.
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.
27 static inline int count_leading_zeros(unsigned long x)
30 return BITS_PER_LONG - fls(x);
32 return BITS_PER_LONG - fls64(x);
35 #define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
38 * count_trailing_zeros - Count the number of zeros from the LSB forwards
41 * Count the number of trailing zeros from the LSB going towards the MSB in @x.
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.
47 static inline int count_trailing_zeros(unsigned long x)
49 #define COUNT_TRAILING_ZEROS_0 (-1)
54 return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
57 #endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */