1.\" $NetBSD: log.3,v 1.7 2019/09/02 00:37:47 sevan Exp $ 2.\" 3.\" Copyright (c) 2011 Jukka Ruohonen <jruohonen@iki.fi> 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 16.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 17.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 18.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 19.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25.\" POSSIBILITY OF SUCH DAMAGE. 26.\" 27.Dd September 2, 2019 28.Dt LOG 3 29.Os 30.Sh NAME 31.Nm log , 32.Nm logf , 33.Nm log10 , 34.Nm log10f , 35.Nm log1p , 36.Nm log1pf , 37.Nm log2 , 38.Nm log2f 39.Nd logarithm functions 40.Sh LIBRARY 41.Lb libm 42.Sh SYNOPSIS 43.In math.h 44.Ft double 45.Fn log "double x" 46.Ft float 47.Fn logf "float x" 48.Ft double 49.Fn log10 "double x" 50.Ft float 51.Fn log10f "float x" 52.Ft double 53.Fn log1p "double x" 54.Ft float 55.Fn log1pf "float x" 56.Ft double 57.Fn log2 "double x" 58.Ft float 59.Fn log2f "float x" 60.Sh DESCRIPTION 61The following functions compute logarithms: 62.Bl -bullet -offset 2n 63.It 64The 65.Fn log 66and 67.Fn logf 68functions return the natural logarithm. 69.It 70The 71.Fn log10 72and 73.Fn log10f 74functions return the base 10 logarithm. 75.It 76The 77.Fn log1p 78and 79.Fn log1pf 80functions return the natural logarithm of (1.0 + 81.Fa x ) 82accurately even for very small values of 83.Fa x . 84.It 85The 86.Fn log2 87and 88.Fn log2f 89functions return the base 2 logarithm. 90.El 91.Sh RETURN VALUES 92Upon successful completion, the functions return the logarithm of 93.Fa x 94as described above. 95Otherwise the following may occur: 96.Bl -enum -offset indent 97.It 98If 99.Fa x 100is \*(Na, all functions return \*(Na. 101.It 102If 103.Fa x 104is positive infinity, all functions return 105.Fa x . 106If 107.Fa x 108is negative infinity, all functions return \*(Na. 109.It 110If 111.Fa x 112is +0.0 or -0.0, the 113.Fn log , 114.Fn log10 , 115and 116.Fn log2 117families return either 118.Dv -HUGE_VAL , 119.Dv -HUGE_VALF , 120or 121.Dv -HUGE_VALL , 122whereas the 123.Fn log1p 124family returns 125.Fa x . 126.It 127If 128.Fa x 129is +1.0, the 130.Fn log , 131.Fn log10 , 132and 133.Fn log2 134families return +0.0. 135If 136.Fa x 137is -1.0, the 138.Fn log1p 139family returns 140.Dv -HUGE_VAL , 141.Dv -HUGE_VALF , 142or 143.Dv -HUGE_VALL . 144.El 145.Pp 146In addition, on a 147.Tn VAX , 148.Va errno 149is set to 150.Er EDOM 151and the reserved operand is returned 152by 153.Fn log 154unless 155.Fa x 156> 0, by 157.Fn log1p 158unless 159.Fa x 160> \-1. 161.Sh SEE ALSO 162.Xr exp 3 , 163.Xr ilogb 3 , 164.Xr math 3 165.Sh STANDARDS 166The described functions conform to 167.St -isoC-99 . 168.Sh HISTORY 169A 170.Fn log 171function appeared in 172.At v1 . 173