1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. 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.\" from: @(#)ffs.3 8.2 (Berkeley) 4/19/94 31.\" $NetBSD: ffs.3,v 1.13 2010/04/28 07:47:09 jruoho Exp $ 32.\" 33.Dd April 28, 2010 34.Dt FFS 3 35.Os 36.Sh NAME 37.Nm ffs 38.Nd find first bit set in a bit string 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In strings.h 43.Ft int 44.Fn ffs "int value" 45.Sh DESCRIPTION 46The 47.Fn ffs 48function finds the first bit set in 49.Fa value 50and returns the index of that bit. 51Bits are numbered starting from 1, starting at the right-most 52bit. 53A return value of 0 means that the argument was zero. 54.Sh SEE ALSO 55.Xr bitstring 3 , 56.Xr ffs32 3 , 57.Xr popcount 3 58.Sh STANDARDS 59The 60.Fn ffs 61function conforms to 62.St -p1003.1-2001 . 63.Sh HISTORY 64The 65.Fn ffs 66function appeared in 67.Bx 4.3 . 68The prototype for it existed previously in the 69.In string.h 70header before it was moved to 71.In strings.h 72for 73.Tn POSIX 74compliance. 75