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FFS(3) Linux Programmer's Manual FFS(3)
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 int i);
int ffsll(long long int i);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
ffs():
Since glibc 2.12:
_SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700
||
Before glibc 2.12:
none
ffsl(), ffsll():
_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
Multithreading (see pthreads(7))
The ffs(), ffsl(), and ffsll() functions are thread-safe.
CONFORMING TO
ffs(): 4.3BSD, POSIX.1-2001.
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 3.74 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 http://www.kernel.org/doc/man-pages/.
GNU 2014-04-14 FFS(3)
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