1.\" Copyright (c) 1990, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Chris Torek. 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" $OpenBSD: ffs.3,v 1.10 2015/11/24 09:14:35 daniel Exp $ 31.\" 32.Dd $Mdocdate: November 24 2015 $ 33.Dt FFS 3 34.Os 35.Sh NAME 36.Nm ffs 37.Nd find first bit set in a bit string 38.Sh SYNOPSIS 39.In strings.h 40.Ft int 41.Fn ffs "int value" 42.Sh DESCRIPTION 43The 44.Fn ffs 45function finds the first bit set in 46.Fa value 47and returns the index of that bit. 48Bits are numbered starting from 1, starting at the rightmost bit. 49A return value of 0 means that the argument was zero. 50.Sh SEE ALSO 51.Xr bitstring 3 52.Sh STANDARDS 53The 54.Fn ffs 55function conforms to 56.St -p1003.1-2008 . 57.Sh HISTORY 58The 59.Fn ffs 60function first appeared in 61.Bx 4.2 . 62