Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 BITS_PER_LONG.
22 */
23static inline int count_leading_zeros(unsigned long x)
24{
25 if (sizeof(x) == 4)
26 return BITS_PER_LONG - fls(x);
27 else
28 return BITS_PER_LONG - fls64(x);
29}
30
31/**
32 * count_trailing_zeros - Count the number of zeros from the LSB forwards
33 * @x: The value
34 *
35 * Count the number of trailing zeros from the LSB going towards the MSB in @x.
36 *
37 * If the LSB of @x is set, the result is 0.
38 * If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
39 * If @x is 0 then the result is BITS_PER_LONG.
40 */
41static inline int count_trailing_zeros(unsigned long x)
42{
43 return x ? __ffs(x) : BITS_PER_LONG;
44}
45
46#endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */