```EXPM1(3)                  Linux Programmer's Manual                 EXPM1(3)
```

## NAME         top

```       expm1, expm1f, expm1l - exponential minus 1
```

## SYNOPSIS         top

```       #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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
expm1f(), expm1l():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION         top

```       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         top

```       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         top

```       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         top

```       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         top

```       C99, POSIX.1-2001, POSIX.1-2008.
```

## BUGS         top

```       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.
```

```       exp(3), log(3), log1p(3)
```

## COLOPHON         top

```       This page is part of release 5.01 of the Linux man-pages project.  A
description of the project, information about reporting bugs, and the