let size x =       if x <=        0x7f then 1 else       if x <=       0x7ff then 2 else       if x <=      0xffff then 3 else       if x <=   0x1f_ffff then 4 else       if x <=  0x3ff_ffff then 5 else       if x <= 0x7fff_ffff then 6 else 0