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expm1, expm1f
[exponential minus 1]

SYNOPSIS

#include <math.h>
double expm1(double x);
float expm1f(float x);

DESCRIPTION

expm1 and expm1f calculate the exponential of x and subtract 1, that is, ex – 1 (where e is the base of the natural system of logarithms, approximately 2.71828).

The result is accurate even for small values of x, where using exp(x)-1 would lose many significant digits.

RETURNS

ex – 1.

COMPLIANCE

Neither expm1 nor expm1f is required by ANSI C or by the System V Interface Definition (Issue 2).