Here is the implementation of get_gray_xy that I used: static uint64_t deinterleave(uint64_t x) { x = x & 0x5555555555555555; x = (x | (x >

Here is the implementation of get_gray_xy that I used: static uint64_t deinterleave(uint64_t x) { x = x & 0x5555555555555555; x = (x | (x >> 1)) & 0x3333333333333333; x = (x | (x >> 2)) & 0x0f0f0f0f0f0f0f0f; x = (x | (x >> 4)) & 0x00ff00ff00ff00ff; x = (x | (x >> 8)) & 0x0000ffff0000ffff; x = (x | (x >> 16)) & 0x00000000ffffffff; return x; } static void get_gray_xy(uint64_t n, uint64_t *x, uint64_t *y) { uint64_t gray = n ^ (n >> 1); *x = deinterleave(gray); *y = deinterleave(gray >> 1); } I don't think the gray code solution can work well for sets of different sizes because the area of indexes that you go through grows as a square. But it does work for different number of dimensions or different number of nested loops. For 3 dimensions each coordinate is constructed from every 3rd bit instead of 2nd. So if you have index 14, then gray code is 9 (1001) which means in two dimensions x=1,y=2 and in three dimensions, x=3,y=0,z=0.