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.\" Chris Torek.
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.\"     from: @(#)ffs.3	8.2 (Berkeley) 4/19/94
.\"	$NetBSD: ffs.3,v 1.14 2024/11/01 18:42:30 riastradh Exp $
.\"
.Dd November 1, 2024
.Dt FFS 3
.Os
.Sh NAME
.Nm ffs
.Nm ffsl
.Nm ffsll
.Nd find first bit set in a bit string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In strings.h
.Ft int
.Fn ffs "int value"
.Fn ffsl "long value"
.Fn ffsll "long long value"
.Sh DESCRIPTION
The
.Fn ffs ,
.Fn ffsl ,
and
.Fn ffsll
functions find the first bit set in
.Fa value
and return the index of that bit.
Bits are numbered starting from 1, starting at the right-most
bit.
A return value of 0 means that the argument was zero.
.Sh SEE ALSO
.Xr bitstring 3 ,
.Xr ffs32 3 ,
.Xr ffs64 3 ,
.Xr popcount 3
.Sh STANDARDS
The
.Fn ffs
function conforms to
.St -p1003.1-2001 .
The
.Fn ffsl
and
.Fn ffsll
functions conform to
.St -p1003.1-2024 .
.Sh HISTORY
The
.Fn ffs
function appeared in
.Bx 4.3 .
The prototype for it existed previously in the
.In string.h
header before it was moved to
.In strings.h
for
.Tn POSIX
compliance.