**expm1**

#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
These functions return a value equivalent to
exp(x) - 1
The result 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 sub-
traction 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.
ATTRIBUTES
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 float-
ing-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.
SEE ALSO
**exp(3)**, **log(3)**, **log1p(3)**
COLOPHON
This page is part of release 4.04 of the Linux man-pages 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/man-pages/.
2015-04-19 **EXPM1(3)**

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