Truncated binary encoding

Truncated binary encoding is an entropy encoding typically used for uniform probability distributions with a finite alphabet. It is parameterized by a maximum number n. It is slightly more general than binary encoding which is only optimal where n is a power of two.

For example, if n is 4, binary encoding allocates these codewords:

Number	Encoding
0	000
1	001
2	010
3	011
4	100
UNUSED	101
UNUSED	110
UNUSED	111

Instead, truncated binary allocates:

Number	Encoding
0	00
1	01
2	10
3	110
4	111

You can think of this as allocating an UNUSED to the first few symbols (until you run out of UNUSEDs), to make the first few symbols' codewords shorter.