1.\" $NetBSD: ilog2.3,v 1.3 2010/06/20 21:57:59 joerg 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 June 8, 2010 31.Dt ILOG2 3 32.Os 33.Sh NAME 34.Nm ilog2 35.Nd integer logarithm 36.Sh SYNOPSIS 37.In sys/bitops.h 38.Ft size 39.Fn ilog2 "size x" 40.Sh DESCRIPTION 41The 42.Fn ilog2 43macro returns an integer (binary) logarithm of 44.Fa x . 45It is the logarithm for base 2; the binary logarithm of 46.Fa x 47is the power to which the number 2 must be raised to obtain the value 48.Fa x . 49.Pp 50The type of the input parameter should be either 51.Vt uint32_t 52or 53.Vt uint64_t . 54.Sh ERRORS 55A value \-1 is returned on error. 56.Sh SEE ALSO 57.Xr log2 3 , 58.Xr imax 9 , 59.Xr powerof2 9 60.Sh HISTORY 61The 62.Fn ilog2 63macro first appeared in 64.Nx 5.0 . 65