//@Description Sketch to swap two bit arrays without using extra storage.

int W = 32;

void swap(ref bit[W] x, ref bit[W] y){		
    int t = ??;
    repeat(t){
        if(??){ x = x ^ y;}else{ y = x ^ y; } 
    }
}

harness void main(bit[W] x, bit[W] y){
    bit[W] tx = x; bit[W] ty = y;
    swap(x, y);
    assert x==ty && y == tx;
}