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. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)ffs.3 8.2 (Berkeley) 4/19/94 35.\" $FreeBSD$ 36.\" 37.Dd October 12, 2006 38.Dt FFS 3 39.Os 40.Sh NAME 41.Nm ffs , 42.Nm ffsl , 43.Nm fls , 44.Nm flsl 45.Nd find first or last bit set in a bit string 46.Sh LIBRARY 47.Lb libc 48.Sh SYNOPSIS 49.In strings.h 50.Ft int 51.Fn ffs "int value" 52.Ft int 53.Fn ffsl "long value" 54.Ft int 55.Fn fls "int value" 56.Ft int 57.Fn flsl "long value" 58.Sh DESCRIPTION 59The 60.Fn ffs 61and 62.Fn ffsl 63functions find the first bit set 64(beginning with the least significant bit) 65in 66.Fa value 67and return the index of that bit. 68.Pp 69The 70.Fn fls 71and 72.Fn flsl 73functions find the last bit set in 74.Fa value 75and return the index of that bit. 76.Pp 77Bits are numbered starting at 1 (the least significant bit). 78A return value of zero from any of these functions means that the 79argument was zero. 80.Sh SEE ALSO 81.Xr bitstring 3 82.Sh HISTORY 83The 84.Fn ffs 85function appeared in 86.Bx 4.3 . 87Its prototype existed previously in 88.In string.h 89before it was moved to 90.In strings.h 91for 92.St -p1003.1-2001 93compliance. 94.Pp 95The 96.Fn ffsl , 97.Fn fls 98and 99.Fn flsl 100functions appeared in 101.Fx 5.3 . 102