FFS
Section: Linux Programmer's Manual (3)
Updated: 2021-03-22
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NAME
ffs, ffsl, ffsll - find first bit set in a word
SYNOPSIS
#include <strings.h>
int ffs(int i);
#include <string.h>
int ffsl(long i);
int ffsll(long long i);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ffs():
Since glibc 2.12:
_XOPEN_SOURCE >= 700
|| ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Before glibc 2.12:
none
ffsl(),
ffsll():
Since glibc 2.27:
_DEFAULT_SOURCE
Before glibc 2.27:
_GNU_SOURCE
DESCRIPTION
The
ffs()
function returns the position of the first
(least significant) bit set in the word i.
The least significant bit is position 1 and the
most significant position is, for example, 32 or 64.
The functions
ffsll()
and
ffsl()
do the same but take
arguments of possibly different size.
RETURN VALUE
These functions return the position of the first bit set,
or 0 if no bits are set in
i.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface | Attribute | Value
|
ffs(),
ffsl(),
ffsll()
| Thread safety | MT-Safe
|
CONFORMING TO
ffs():
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The
ffsl()
and
ffsll()
functions are glibc extensions.
NOTES
BSD systems have a prototype in
<string.h>.
SEE ALSO
memchr(3)
COLOPHON
This page is part of release 5.11 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 06:22:47 GMT, May 09, 2021