**log1pl**

**LOG1P(3)** Linux Programmer's Manual **LOG1P(3)**
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
These functions return a value equivalent to
log (1 + x)
The result 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 floating-point exception (FE_INVALID) is raised.
Pole error: x is -1
A divide-by-zero floating-point exception (FE_DIVBYZERO) is
raised.
These functions do not set errno.
ATTRIBUTES
For an explanation of the terms used in this section, see
**attributes(7)**.
+----------------------------+---------------+---------+
|Interface | Attribute | Value |
+----------------------------+---------------+---------+
|log1p(), log1pf(), log1pl() | Thread safety | MT-Safe |
+----------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
SEE ALSO
**exp(3)**, **expm1(3)**, **log(3)**
COLOPHON
This page is part of release 4.04 of the Linux man-pages 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/man-pages/.
2015-04-19 **LOG1P(3)**

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