EXPM1
Section: Linux Programmer's Manual (3)
Updated: 20170915
Page Index
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);
Link with
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
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
zeroa 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 floatingpoint 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  MTSafe

CONFORMING TO
C99, POSIX.12001, POSIX.12008.
BUGS
For some large negative
x
values (where the function result approaches 1),
expm1()
raises a bogus underflow floatingpoint exception.
For some large positive
x
values,
expm1()
raises a bogus invalid floatingpoint 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.
SEE ALSO
exp(3),
log(3),
log1p(3)
COLOPHON
This page is part of release 5.02 of the Linux
manpages
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/manpages/.