Question: How do I get stable results of the "HeunC"-function for large parameters?

I would like to compute the function 

                       f(x) := exp(x) * HeunC(2*x, 1/2, -1/2, -x^2, 1/8, 99/100)

for very large real values of x. However, in the following plot it can be seen that there are already strong numerical instabilities for x>33. What can I do to reach more stability for large x? Or, does somebody know how to get a closed form asymptotic expression for large x?


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