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`expm1', `expm1f'--exponential minus 1

     #include <math.h>
     double expm1(double X);
     float expm1f(float X);
`expm1' and `expm1f' calculate the exponential of X and subtract 1,
that is, e raised to the power X minus 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.
e raised to the power X, minus 1.
Neither `expm1' nor `expm1f' is required by ANSI C or by the System V
Interface Definition (Issue 2).