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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():
_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

```       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.

```

#### 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
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 │
└────────────────────────────┴───────────────┴─────────┘
```

#### CONFORMINGTO

```       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.

```

#### SEEALSO

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

```

#### COLOPHON

```       This page is part of release 5.02 of the Linux man-pages project.  A  description  of  the