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(): expm1f(), expm1l():

DESCRIPTION¶

expm1(x) returns a value equivalent to

    exp(x) - 1

It 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¶

Multithreading (see pthreads(7))¶

The expm1(), expm1f(), and expm1l() functions are thread-safe.

CONFORMING TO¶

C99, POSIX.1-2001.

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.

SEE ALSO¶

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

COLOPHON¶

This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.