# log1p

```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);

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.