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 1.14 2024/11/01 18:42:30 riastradh Exp $ 32.\" 33.Dd November 1, 2024 34.Dt FFS 3 35.Os 36.Sh NAME 37.Nm ffs 38.Nm ffsl 39.Nm ffsll 40.Nd find first bit set in a bit string 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In strings.h 45.Ft int 46.Fn ffs "int value" 47.Fn ffsl "long value" 48.Fn ffsll "long long value" 49.Sh DESCRIPTION 50The 51.Fn ffs , 52.Fn ffsl , 53and 54.Fn ffsll 55functions find the first bit set in 56.Fa value 57and return the index of that bit. 58Bits are numbered starting from 1, starting at the right-most 59bit. 60A return value of 0 means that the argument was zero. 61.Sh SEE ALSO 62.Xr bitstring 3 , 63.Xr ffs32 3 , 64.Xr ffs64 3 , 65.Xr popcount 3 66.Sh STANDARDS 67The 68.Fn ffs 69function conforms to 70.St -p1003.1-2001 . 71The 72.Fn ffsl 73and 74.Fn ffsll 75functions conform to 76.St -p1003.1-2024 . 77.Sh HISTORY 78The 79.Fn ffs 80function appeared in 81.Bx 4.3 . 82The prototype for it existed previously in the 83.In string.h 84header before it was moved to 85.In strings.h 86for 87.Tn POSIX 88compliance. 89