Please rid me of this goto

[deadalnix via Digitalmars-d]

On Thursday, 23 June 2016 at 17:22:55 UTC, Andrei Alexandrescu 
wrote:
> 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

The inner loop is not a loop, so that's not a problem:

// Loop invariant: r * (b ^^ e) is the actual result
while(true) {
   if (e % 2 != 0) {
     r = mul(r, b, overflow);
     if (e == 1) return r;
   }

   b = mul(b, b, overflow);
   e /= 2;
}