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.\" @(#)ffs.3 8.2 (Berkeley) 4/19/94 31.\" $FreeBSD$ 32.\" 33.Dd October 17, 2015 34.Dt FFS 3 35.Os 36.Sh NAME 37.Nm ffs , 38.Nm ffsl , 39.Nm ffsll , 40.Nm fls , 41.Nm flsl , 42.Nm flsll 43.Nd find first or last bit set in a bit string 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In strings.h 48.Ft int 49.Fn ffs "int value" 50.Ft int 51.Fn ffsl "long value" 52.Ft int 53.Fn ffsll "long long value" 54.Ft int 55.Fn fls "int value" 56.Ft int 57.Fn flsl "long value" 58.Ft int 59.Fn flsll "long long value" 60.Sh DESCRIPTION 61The 62.Fn ffs , 63.Fn ffsl 64and 65.Fn ffsll 66functions find the first (least significant) bit set 67in 68.Fa value 69and return the index of that bit. 70.Pp 71The 72.Fn fls , 73.Fn flsl 74and 75.Fn flsll 76functions find the last (most significant) bit set in 77.Fa value 78and return the index of that bit. 79.Pp 80Bits are numbered starting at 1, the least significant bit. 81A return value of zero from any of these functions means that the 82argument was zero. 83.Sh SEE ALSO 84.Xr bitstring 3 , 85.Xr bitset 9 86.Sh HISTORY 87The 88.Fn ffs 89function appeared in 90.Bx 4.3 . 91Its prototype existed previously in 92.In string.h 93before it was moved to 94.In strings.h 95for 96.St -p1003.1-2001 97compliance. 98.Pp 99The 100.Fn ffsl , 101.Fn fls 102and 103.Fn flsl 104functions appeared in 105.Fx 5.3 . 106The 107.Fn ffsll 108and 109.Fn flsll 110functions appeared in 111.Fx 7.1 . 112