1.\" Copyright (c) 2008 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 January 17, 2008 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 log1p , 37.Nm log1pf 38.Nd logarithm functions 39.Sh LIBRARY 40.Lb libm 41.Sh SYNOPSIS 42.In math.h 43.Ft double 44.Fn log "double x" 45.Ft float 46.Fn logf "float x" 47.Ft double 48.Fn log10 "double x" 49.Ft float 50.Fn log10f "float x" 51.Ft double 52.Fn log1p "double x" 53.Ft float 54.Fn log1pf "float x" 55.Sh DESCRIPTION 56The 57.Fn log 58and 59.Fn logf 60functions compute the natural logarithm of 61.Fa x . 62.Pp 63The 64.Fn log10 65and 66.Fn log10f 67functions compute the logarithm base 10 of 68.Fa x . 69.Pp 70The 71.Fn log1p 72and 73.Fn log1pf 74functions compute the natural logarithm of 75.No "1 + x" . 76Computing the natural logarithm as 77.Li log1p(x) 78is more accurate than computing it as 79.Li log(1 + x) 80when 81.Fa x 82is close to zero. 83.Sh RETURN VALUES 84These functions return the requested logarithm; the logarithm of 1 is +0. 85An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero 86exception, and -\*(If is returned. 87Otherwise, attempting to take the logarithm of a negative number 88results in an invalid exception and a return value of \*(Na. 89.Sh SEE ALSO 90.Xr exp 3 , 91.Xr ilogb 3 , 92.Xr math 3 , 93.Xr pow 3 94.Sh STANDARDS 95The 96.Fn log , 97.Fn logf , 98.Fn log10 , 99.Fn log10f , 100.Fn log1p , 101and 102.Fn log1pf 103functions conform to 104.St -isoC-99 . 105