public static Accumulator operator *(Accumulator accumulator, double y)
{
double d = accumulator._s;
accumulator._s *= y;
d = GeoMath.Fma(y, d, -accumulator._s); // error in firt multiplication
accumulator._t = GeoMath.Fma(y, accumulator._t, d); // error in second term
return(accumulator);
}