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LOG1P
Linux Programmer's Manual (3)
20140228
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
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Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 ATTRIBUTES

 Multithreading (see pthreads(7))

 CONFORMING TO

 SEE ALSO

 COLOPHON

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