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 January 13, 2004 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 in 64.Fa value 65and return the index of that bit. 66.Pp 67The 68.Fn fls 69and 70.Fn flsl 71functions find the last bit set in 72.Fa value 73and return the index of that bit. 74.Pp 75Bits are numbered starting from 1, starting at the right-most 76(least significant) bit. 77A return value of zero from any of these functions means that the 78argument was zero. 79.Sh SEE ALSO 80.Xr bitstring 3 81.Sh HISTORY 82The 83.Fn ffs 84function appeared in 85.Bx 4.3 . 86Its prototype existed previously in 87.In string.h 88before it was moved to 89.In strings.h 90for 91.St -p1003.1-2001 92compliance. 93.Pp 94The 95.Fn ffsl , 96.Fn fls 97and 98.Fn flsl 99functions appeared in 100.Fx 5.3 . 101