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

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
expm1 (), expm1f (), expm1l ()	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.

SEE ALSO

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