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 3.65 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.