[Issue 19732] make std.complex.expi fast.

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19732

--- Comment #5 from Bastiaan Veelo <Bastiaan at Veelo.net> ---
Maybe there should be a std.math.sincos that does not depend on complex numbers
at all?

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