Semantics of ^^

[Steven Schveighoffer]

On Tue, 08 Dec 2009 05:32:26 -0500, Don <nospam at nospam.com> wrote:

> Based on everyone's comments, this is what I have come up with:
>
> --------------------
> x ^^ y is right associative, and has a precedence intermediate between  
> multiplication and unary operators.
>
> * The type of x ^^ y is the same as the type of x * y.
> * If y == 0,  x ^^ y is 1.
> * If both x and y are integers, and y > 0,  x^^y is equivalent to
>     { auto u = x; foreach(i; 1..y) { u *= x; } return u; }
> * If both x and y are integers, and y < 0, an integer divide error  
> occurs, regardless of the value of x. This error is detected at compile  
> time, if possible.
> * If either x or y are floating-point, the result is pow(x, y).

If x and y are both integral and x is 2, then the operation becomes 1 << y

Also, what happens when you do 3^^1000000?  I hope this does not result in  
the exact loop you wrote above.

At the very least, when y > 32, the following code is more efficient:

{
   /* get largest set bit, probably could do this more efficiently, note  
that the type of m and y should be unsigned */
   typeof(y) m = 1 << (typeof(y).sizeof * 8 - 1);
   while(m > y)
       m >>= 1;

   long u = 1;
   for(; m > 0; m >>=1)
   {
     u *= u;
     if(m & y)
       u *= x;
   }
   return u;
}

-Steve