2017-09-15

Aliases: expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1f(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), expm1l(3), log1p(3), log1p(3), log1p(3)

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## NAME

expm1, expm1f, expm1l - exponential minus 1

## SYNOPSIS

Link with#include <math.h>

double expm1(doublex);float expm1f(floatx);long double expm1l(long doublex);

*-lm*.

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

|| _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

|| /* 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.## 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 |

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.## COLOPHON

This page is part of release 5.00 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 https://www.kernel.org/doc/man-pages/.