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.\" 4. 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 12, 2006 34.Dt FFS 3 35.Os 36.Sh NAME 37.Nm ffs , 38.Nm ffsl , 39.Nm fls , 40.Nm flsl 41.Nd find first or last bit set in a bit string 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In strings.h 46.Ft int 47.Fn ffs "int value" 48.Ft int 49.Fn ffsl "long value" 50.Ft int 51.Fn fls "int value" 52.Ft int 53.Fn flsl "long value" 54.Sh DESCRIPTION 55The 56.Fn ffs 57and 58.Fn ffsl 59functions find the first bit set 60(beginning with the least significant bit) 61in 62.Fa value 63and return the index of that bit. 64.Pp 65The 66.Fn fls 67and 68.Fn flsl 69functions find the last bit set in 70.Fa value 71and return the index of that bit. 72.Pp 73Bits are numbered starting at 1 (the least significant bit). 74A return value of zero from any of these functions means that the 75argument was zero. 76.Sh SEE ALSO 77.Xr bitstring 3 78.Sh HISTORY 79The 80.Fn ffs 81function appeared in 82.Bx 4.3 . 83Its prototype existed previously in 84.In string.h 85before it was moved to 86.In strings.h 87for 88.St -p1003.1-2001 89compliance. 90.Pp 91The 92.Fn ffsl , 93.Fn fls 94and 95.Fn flsl 96functions appeared in 97.Fx 5.3 . 98