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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 $
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.Dd October 26, 2008
.Dt FFS 3
.Os
.Sh NAME
.Nm ffs ,
.Nm ffsl ,
.Nm ffsll ,
.Nm fls ,
.Nm flsl ,
.Nm flsll
.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 value"
.Ft int
.Fn ffsl "long value"
.Ft int
.Ft int
.Fn ffsll "long long value"
.Fn fls "int value"
.Ft int
.Fn flsl "long value"
.Ft int
.Fn flsll "long long value"
.Sh DESCRIPTION
The
.Fn ffs ,
.Fn ffsl
and
.Fn ffsll
functions find the first bit set
(beginning with the least significant bit)
in
.Fa value
and return the index of that bit.
.Pp
The
.Fn fls ,
.Fn flsl
and
.Fn flsll
functions find the last bit set in
.Fa value
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 .
The
.Fn ffsll
and
.Fn flsll
functions appeared in
.Fx 7.1 .