[pbafqzwx] Notes on QR code

Decimal strings are encoded as 3 digits per 10 bits (because 1000 < 1024). Entropy per bit is 0.9965784284662087043610958288.

"Alphanumeric" is base 45, using the following "digits" in this order.

0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:

Two digits per 11 bits (because 45*45 = 2025 < 2048). Entropy per bit is 0.9985187447872135837777813304

From looking at the source code to libqrencode by FUKUCHI Kentaro