1.\" $NetBSD: ffs32.3,v 1.6 2011/04/08 08:47:50 wiz Exp $ 2.\" 3.\" Copyright (c) 2010 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jukka Ruohonen. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd April 8, 2011 31.Dt FFS32 3 32.Os 33.Sh NAME 34.Nm ffs32 , 35.Nm ffs64 , 36.Nm fls32 , 37.Nm fls64 38.Nd find first or last bit set 39.Sh SYNOPSIS 40.In sys/bitops.h 41.Ft int 42.Fn ffs32 "uint32_t n" 43.Ft int 44.Fn ffs64 "uint64_t n" 45.Ft int 46.Fn fls32 "uint32_t n" 47.Ft int 48.Fn fls64 "uint64_t n" 49.Sh DESCRIPTION 50The 51.Fn ffs32 52and 53.Fn ffs64 54functions find the first bit set in 55.Fa n 56and return the index of that bit. 57Conversely, 58the 59.Fn fls32 60and 61.Fn fls64 62functions find the last bit set in 63.Fa n , 64returning the index of the bit. 65.Pp 66The search always starts from the bit 1 (the least significant bit). 67If the argument 68.Fa n 69is zero, each function returns zero. 70.Sh IMPLEMENTATION NOTES 71The described functions are implemented as 72.Em static inline 73functions in the 74.In sys/bitops.h 75header. 76The standard C library includes a more portable 77.Xr ffs 3 78for user applications. 79.\" 80.\" XXX: It is noted in the CVS history of <sys/bitops.h> that MD-optimized 81.\" <machine/bitops.h> is a TODO. If those start to appear, note it here. 82.\" 83.Sh EXAMPLES 84In the following example 85.Va f = 3 86and 87.Va l = 7 : 88.Bd -literal -offset indent 89uint32_t n = 0x44; /* 01000100 */ 90int f, l; 91 92f = ffs32(n); 93l = fls32(n); 94.Ed 95.Sh SEE ALSO 96.Xr bitops 3 , 97.Xr bits 3 , 98.Xr bitstring 3 , 99.Xr ffs 3 , 100.Xr setbit 9 101.Sh HISTORY 102These functions first appeared in 103.Nx 5.0 . 104