BCD (Binary Coded Decimals) is a common way to encode integer numbers in a way that makes human-readable output somewhat simpler. In this encoding scheme, every decimal digit is encoded as either a single byte (8 bits), or a nibble (half of a byte, 4 bits). This obviously wastes a lot of bits, but it makes translation into human-readable string much easier than traditional binary-to-decimal conversion process, which includes lots of divisions by 10.

For example, encoding integer 31337 in 8-digit, 8 bits per digit, big endian order of digits BCD format yields

```
00 00 00 03 01 03 03 07
```

Encoding the same integer as 8-digit, 4 bits per digit, little endian order BCD format would yield:

```
73 31 30 00
```

Using this type of encoding in Kaitai Struct is pretty
straightforward: one calls for this type, specifying desired
encoding parameters, and gets result using either `as_int`

or
`as_str`

attributes.

This page hosts a formal specification of BCD (Binary Coded Decimals) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.