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`asinh', `asinhf'--inverse hyperbolic sine

     #include <math.h>
     double asinh(double X);
     float asinhf(float X);
`asinh' calculates the inverse hyperbolic sine of X.  `asinh' is
defined as
      sgn(X) * log(abs(X) + sqrt(1+X*X))
   `asinhf' is identical, other than taking and returning floats.
`asinh' and `asinhf' return the calculated value.
Neither `asinh' nor `asinhf' are ANSI C.