Manual Reference Pages - LOG1P (3)
NAME
log1p, log1pf, log1pl - logarithm of 1 plus argument
CONTENTS
Synopsis
Description
Return Value
Errors
Colophon
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 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 .
CONFORMING TO
C99, POSIX.1-2001.
SEE ALSO
exp (3),
expm1 (3),
log (3)
COLOPHON
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man-pages project.
A description of the project,
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can be found at
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