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## 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 ||
_ISOC99_SOURCE; or cc -std=c99
expm1f(), expm1l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; 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.

```

## RETURNVALUE

```       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
An overflow floating-point exception (FE_OVERFLOW) is raised.

These functions do not set errno.

```

## CONFORMINGTO

```       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.

```

```       exp(3), log(3), log1p(3)
```       This page is part of release 3.24 of the Linux  man-pages  project.   A