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 June 3, 2013 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 log10l , 37.Nm log2 , 38.Nm log2f , 39.Nm log2l , 40.Nm log1p , 41.Nm log1pf , 42.Nm log1pl 43.Nd logarithm functions 44.Sh LIBRARY 45.Lb libm 46.Sh SYNOPSIS 47.In math.h 48.Ft double 49.Fn log "double x" 50.Ft float 51.Fn logf "float x" 52.Ft long double 53.Fn logl "long double x" 54.Ft double 55.Fn log10 "double x" 56.Ft float 57.Fn log10f "float x" 58.Ft long double 59.Fn log10l "long double x" 60.Ft double 61.Fn log2 "double x" 62.Ft float 63.Fn log2f "float x" 64.Ft long double 65.Fn log2l "long double x" 66.Ft double 67.Fn log1p "double x" 68.Ft float 69.Fn log1pf "float x" 70.Ft long double 71.Fn log1pl "long double x" 72.Sh DESCRIPTION 73The 74.Fn log , 75.Fn logf , 76and 77.Fn logl 78functions compute the natural logarithm of 79.Fa x . 80.Pp 81The 82.Fn log10 , 83.Fn log10f , 84and 85.Fn log10l 86functions compute the logarithm base 10 of 87.Fa x , 88while 89.Fn log2 , 90.Fn log2f , 91and 92.Fn log2l 93compute the logarithm base 2 of 94.Fa x . 95.Pp 96The 97.Fn log1p , 98.Fn log1pf , 99and 100.Fn log1pl 101functions compute the natural logarithm of 102.No "1 + x" . 103Computing the natural logarithm as 104.Li log1p(x) 105is more accurate than computing it as 106.Li log(1 + x) 107when 108.Fa x 109is close to zero. 110.Sh RETURN VALUES 111These functions return the requested logarithm; the logarithm of 1 is +0. 112An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero 113exception, and -\*(If is returned. 114Otherwise, attempting to take the logarithm of a negative number 115results in an invalid exception and a return value of \*(Na. 116.Sh SEE ALSO 117.Xr exp 3 , 118.Xr ilogb 3 , 119.Xr math 3 , 120.Xr pow 3 121.Sh STANDARDS 122The 123.Fn log , 124.Fn logf , 125.Fn logl , 126.Fn log10 , 127.Fn log10f , 128.Fn log10l , 129.Fn log2 , 130.Fn log2f , 131.Fn log2l , 132.Fn log1p , 133.Fn log1pf , 134and 135.Fn log1pl 136functions conform to 137.St -isoC-99 . 138