Question

I am building a quadtree using the techniques described in this wikipedia article.
I am storing the coordinates in an 2- or 3-dimansional array.

boost::array<unsigned int, 2 /* 3 */> coord;

I need a method to calculate the coordinates of the next box in z-order.
It would work by interleaving the bits, increasing by one and than deinterleaving, but this gets very complicated.
I hope there is an implementation similar to the cmp_zorder(…) methon in the article wich works without interleaving the bits.

Answer 1

Ok here’s the “mutilated” addition algorithm, x and y are inputs as well as outputs, and it is assumed that the lowest order bit in the interleaved coordinate would be x (the same as in the wikipedia article)

int carry = 1;
do
{
    int newcarry = x & carry;
    x ^= carry;
    carry = newcarry;
    newcarry = (y & carry) << 1;
    y ^= carry;
    carry = newcarry;
} while (carry != 0);

I did test it, but only a little.