EXPM1

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
BUGS
SEE ALSO
COLOPHON

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NAME

expm1, expm1f, expm1l − exponential minus 1

SYNOPSIS

#include

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
|| /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Since glibc 2.19: bodies/ usr/ _DEFAULT_SOURCE
|| /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Glibc versions <= 2.19: bodies/ usr/ _BSD_SOURCE || _SVID_SOURCE

expm1f(), expm1l():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Since glibc 2.19: bodies/ usr/ _DEFAULT_SOURCE
|| /bin /boot /dead.letter /dev /etc /home /initrd /lib /lib64 /lost+found /media /mnt /opt /proc /release-notes.html /release-notes.txt /root /run /sbin /srv /sys /tmp /usr /var Glibc versions <= 2.19: bodies/ usr/ _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).

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 exception, 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 5.10 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/.

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