A simple way to do the latter is

  for(u64 x = -m & m; ;x = (x - m) & m) {
    const u64 r = x ^ m;
    for(u64 t = -x & x; ; t = (t - x) & x) {
      const u64 z = r | t;
      // Use (x,z)
      if(t == 0) break;
    }
    if(x==0) break;
  }