Please rid me of this goto

[Andrei Alexandrescu via Digitalmars-d]

So I was looking for an efficient exponentiation implementation, and 
http://www.stepanovpapers.com/PAM.pdf has a nice discussion starting at 
page 54. Stepanov's solution, however, duplicates code, so I eliminated it:

https://dpaste.dzfl.pl/e53acb41885a

The cost is the use of one goto. Can the code be restructured to not 
need it?


Thanks,

Andrei