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EXPM1
Linux Programmer's Manual (3)
20131014
NAME
expm1, expm1f, expm1l  exponential minus 1
SYNOPSIS
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
Link with
lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
expm1():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 500 
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
expm1f(),
expm1l():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
DESCRIPTION
expm1(x)
returns a value equivalent to
exp(x)  1
It is
computed in a way that is accurate even if the value of
x
is near
zeroa case where
exp(x)  1
would be inaccurate due to
subtraction of two numbers that are nearly equal.
RETURN VALUE
On success, these functions return
exp(x)  1.
If
x
is a NaN,
a NaN is returned.
If
x
is +0 (0),
+0 (0) is returned.
If
x
is positive infinity, positive infinity is returned.
If
x
is negative infinity, 1 is returned.
If the result overflows, a range error occurs,
and the functions return
HUGE_VAL,
HUGE_VALF,
or
HUGE_VALL,
respectively.
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:
 Range error, overflow

errno
is set to
ERANGE
(but see BUGS).
An overflow floatingpoint exception
(FE_OVERFLOW)
is raised.
ATTRIBUTES
Multithreading (see pthreads(7))
The
expm1(),
expm1f(),
and
expm1l()
functions are threadsafe.
CONFORMING TO
C99, POSIX.12001.
BUGS
For some large negative
x
values (where the function result approaches 1),
expm1()
raises a bogus underflow floatingpoint exception.
For some large positive
x
values,
expm1()
raises a bogus invalid floatingpoint exception in addition to the expected
overflow exception, and returns a NaN instead of positive infinity.
Before version 2.11,
the glibc implementation did not set
errno
to
ERANGE
when a range error occurred.
SEE ALSO
exp(3),
log(3),
log1p(3)
COLOPHON
This page is part of release 3.66 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

 BUGS

 SEE ALSO

 COLOPHON

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