_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
zero---a 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 floating-point exception
(FE_OVERFLOW)
is raised.

CONFORMING TO

C99, POSIX.1-2001.

BUGS

For some large negative
x
values (where the function result approaches -1),
expm1()
raises a bogus underflow floating-point exception.

For some large positive
x
values,
expm1()
raises a bogus invalid floating-point 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.

This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.