FFS

Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
Index Return to Main Contents

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.

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>.

COLOPHON

This page is part of release 3.27 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/.

This document was created by man2html, using the manual pages.
Time: 19:49:21 GMT, April 27, 2011

FFS