relibc_openlibm/man/log.3

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.\" $FreeBSD: src/lib/msun/man/log.3,v 1.2 2010/12/05 22:11:22 das Exp $
.\"
.Dd December 5, 2010
.Dt LOG 3
.Os
.Sh NAME
.Nm log ,
.Nm logf ,
.Nm logl ,
.Nm log10 ,
.Nm log10f ,
.Nm log2 ,
.Nm log2f ,
.Nm log1p ,
.Nm log1pf
.Nd logarithm functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn log "double x"
.Ft float
.Fn logf "float x"
.Ft double
.Fn log10 "double x"
.Ft float
.Fn log10f "float x"
.Ft double
.Fn log2 "double x"
.Ft float
.Fn log2f "float x"
.Ft double
.Fn log1p "double x"
.Ft float
.Fn log1pf "float x"
.Sh DESCRIPTION
The
.Fn log
and
.Fn logf
functions compute the natural logarithm of
.Fa x .
.Pp
The
.Fn log10
and
.Fn log10f
functions compute the logarithm base 10 of
.Fa x ,
while
.Fn log2
and
.Fn log2f
compute the logarithm base 2 of
.Fa x .
.Pp
The
.Fn log1p
and
.Fn log1pf
functions compute the natural logarithm of
.No "1 + x" .
Computing the natural logarithm as
.Li log1p(x)
is more accurate than computing it as
.Li log(1 + x)
when
.Fa x
is close to zero.
.Sh RETURN VALUES
These functions return the requested logarithm; the logarithm of 1 is +0.
An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero
exception, and -\*(If is returned.
Otherwise, attempting to take the logarithm of a negative number
results in an invalid exception and a return value of \*(Na.
.Sh SEE ALSO
.Xr exp 3 ,
.Xr ilogb 3 ,
.Xr math 3 ,
.Xr pow 3
.Sh STANDARDS
The
.Fn log ,
.Fn logf ,
.Fn log10 ,
.Fn log10f ,
.Fn log2 ,
.Fn log2f ,
.Fn log1p ,
and
.Fn log1pf
functions conform to
.St -isoC-99 .