Calculate (x^y)%z without pow()

Problem:
Calculate (x^y)%z without pow().

Solution:
The question here is how we can reduce the complexity... if we compute the x^y by normal method the complexity is O(y)... to reduce the complexity we can use binary weighted power computation method in which complexity is O(logy)..

ans=1;
square=x;
if(y==0)
    return 1;
while(y!=0)
{
    if(y%2)
        ans=ans*square;
    square=(square*square)%z;
    y=y/2;
    if(ans>z)
        ans=ans%z;
}
return ans;

Complexity:

time - O(log n)
space - O(1)

Links and credits:
http://www.careercup.com/question?id=22767685