1.\" Copyright (c) 2008-2010 David Schultz <das@FreeBSD.org> 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd December 5, 2010 28.Dt LOG 3 29.Os 30.Sh NAME 31.Nm log , 32.Nm logf , 33.Nm logl , 34.Nm log10 , 35.Nm log10f , 36.Nm log2 , 37.Nm log2f , 38.Nm log1p , 39.Nm log1pf 40.Nd logarithm functions 41.Sh LIBRARY 42.Lb libm 43.Sh SYNOPSIS 44.In math.h 45.Ft double 46.Fn log "double x" 47.Ft float 48.Fn logf "float x" 49.Ft double 50.Fn log10 "double x" 51.Ft float 52.Fn log10f "float x" 53.Ft double 54.Fn log2 "double x" 55.Ft float 56.Fn log2f "float x" 57.Ft double 58.Fn log1p "double x" 59.Ft float 60.Fn log1pf "float x" 61.Sh DESCRIPTION 62The 63.Fn log 64and 65.Fn logf 66functions compute the natural logarithm of 67.Fa x . 68.Pp 69The 70.Fn log10 71and 72.Fn log10f 73functions compute the logarithm base 10 of 74.Fa x , 75while 76.Fn log2 77and 78.Fn log2f 79compute the logarithm base 2 of 80.Fa x . 81.Pp 82The 83.Fn log1p 84and 85.Fn log1pf 86functions compute the natural logarithm of 87.No "1 + x" . 88Computing the natural logarithm as 89.Li log1p(x) 90is more accurate than computing it as 91.Li log(1 + x) 92when 93.Fa x 94is close to zero. 95.Sh RETURN VALUES 96These functions return the requested logarithm; the logarithm of 1 is +0. 97An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero 98exception, and -\*(If is returned. 99Otherwise, attempting to take the logarithm of a negative number 100results in an invalid exception and a return value of \*(Na. 101.Sh SEE ALSO 102.Xr exp 3 , 103.Xr ilogb 3 , 104.Xr math 3 , 105.Xr pow 3 106.Sh STANDARDS 107The 108.Fn log , 109.Fn logf , 110.Fn log10 , 111.Fn log10f , 112.Fn log2 , 113.Fn log2f , 114.Fn log1p , 115and 116.Fn log1pf 117functions conform to 118.St -isoC-99 . 119