EXPM1(3) Linux Programmer's Manual EXPM1(3)
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 zero--a case where exp(x) - 1 would be inaccurate due to sub-
traction 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 at-
tributes(7).
+----------------------------+---------------+---------+
|Interface | Attribute | Value |
+----------------------------+---------------+---------+
|expm1(), expm1f(), expm1l() | Thread safety | MT-Safe |
+----------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
BUGS
Before glibc 2.17, on certain architectures (e.g., x86, but not x86_64)
expm1() raised a bogus underflow floating-point exception for some
large negative x values (where the function result approaches -1),
Before approximately glibc version 2.11, expm1() raised a bogus invalid
floating-point exception in addition to the expected overflow excep-
tion, and returned a NaN instead of positive infinity. for some large
positive x values,
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 5.07 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/.
2020-06-09 EXPM1(3)