SIMPLE SOLUTIONS

# EXPM1(3) - man page online | library functions

Exponential minus 1.

Chapter
2015-04-19
```EXPM1(3)                            Linux Programmer's Manual                            EXPM1(3)

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);

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 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.

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).

┌────────────────────────────┬───────────────┬─────────┐
│Interface                   │ Attribute     │ Value   │
├────────────────────────────┼───────────────┼─────────┤
│expm1(), expm1f(), expm1l() │ Thread safety │ MT-Safe │
└────────────────────────────┴───────────────┴─────────┘
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

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.