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.\"     @(#)ffs.3	8.2 (Berkeley) 4/19/94
.\" $FreeBSD: src/lib/libc/string/ffs.3,v 1.13 2009/01/13 13:19:42 kib Exp $
.\"
.Dd October 26, 2008
.Dt FFS 3
.Os
.Sh NAME
.Nm ffs ,
.Nm ffsl ,
.Nm fls ,
.Nm flsl
.Nd find first or last bit set in a bit string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In strings.h
.Ft int
.Fn ffs "int i"
.Ft int
.Fn ffsl "long i"
.Ft int
.Fn fls "int i"
.Ft int
.Fn flsl "long i"
.Sh DESCRIPTION
The
.Fn ffs
and
.Fn ffsl
functions find the first bit set
(beginning with the least significant bit)
in
.Fa i
and return the index of that bit.
.Pp
The
.Fn fls
and
.Fn flsl
functions find the last bit set in
.Fa i
and return the index of that bit.
.Pp
Bits are numbered starting at 1 (the least significant bit).
A return value of zero from any of these functions means that the
argument was zero.
.Sh SEE ALSO
.Xr bitstring 3
.Sh HISTORY
The
.Fn ffs
function appeared in
.Bx 4.3 .
Its prototype existed previously in
.In string.h
before it was moved to
.In strings.h
for
.St -p1003.1-2001
compliance.
.Pp
The
.Fn ffsl ,
.Fn fls ,
and
.Fn flsl
functions appeared in
.Fx 5.3 .