LOG1P
Section: Linux Programmer's Manual (3)
Updated: 20140228
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NAME
log1p, log1pf, log1pl  logarithm of 1 plus argument
SYNOPSIS
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
Link with
lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
log1p():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 500 
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
log1pf(),
log1pl():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
DESCRIPTION
log1p(x)
returns a value equivalent to
log (1 + x)
It is computed in a way
that is accurate even if the value of
x
is near zero.
RETURN VALUE
On success, these functions return the natural logarithm of
(1 + x).
If
x
is a NaN,
a NaN is returned.
If
x
is positive infinity, positive infinity is returned.
If
x
is 1, a pole error occurs,
and the functions return
HUGE_VAL,
HUGE_VALF,
or
HUGE_VALL,
respectively.
If
x
is less than 1 (including negative infinity),
a domain error occurs,
and a NaN (not a number) is returned.
ERRORS
See
math_error(7)
for information on how to determine whether an error has occurred
when calling these functions.
The following errors can occur:
 Domain error: x is less than 1

An invalid floatingpoint exception
(FE_INVALID)
is raised.
 Pole error: x is 1

A dividebyzero floatingpoint exception
(FE_DIVBYZERO)
is raised.
These functions do not set
errno.
ATTRIBUTES
Multithreading (see pthreads(7))
The
log1p(),
log1pf(),
and
log1pl()
functions are threadsafe.
CONFORMING TO
C99, POSIX.12001.
SEE ALSO
exp(3),
expm1(3),
log(3)
COLOPHON
This page is part of release 3.74 of the Linux
manpages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
http://www.kernel.org/doc/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 ATTRIBUTES

 Multithreading (see pthreads(7))

 CONFORMING TO

 SEE ALSO

 COLOPHON
