J2ME power(double, double) math function implement

问题:

I want to implement math function power to double, can you advice algorithm for this?

I've reviewed sources of Java ME Open Source Software - Math but I want to implement it from the scratch.

Thank you!

回答1:

I don't know J2ME well enough to know, but do you have Math.log() and Math.exp() ?

Then you can simply use this relation:

x^y = exp(y * log(x))

If you don't have the aforementioned two functions, then you should start by implementing those. As far as I know, the above relation is the only reasonable way to compute x^y.

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Update: I see the paper linked in kusman's answer shows an alternative way to do pow using the idea of a fractional exponent. Quite cool! But the paper also shows the "normal" way to do things via multiplication of the log, and shows you how to implement Taylor series for exp() and log().