ceil(log2(x))
-------------
1..         8:  3
1..        16:  4
1..        32:  5
1..        64:  6
1..       128:  7
1..       256:  8
1..       512:  9
1..      1024: 10
1..        10:  4
1..       100:  7
1..     1,000: 10
1..    10,000: 14
1..   100,000: 17
1.. 1,000,000: 20
1..10,000,000: 24