QR code (2D barcode) coding and decoding algorithms?

I have a colleague who worked on ZXing ("Zebra Crossing").

That's got a fair variety of platform support.

http://www.swetake.com/qrcode/qr1_en.html

Just thought I'd mention this one which is explaining HOW they work.

QR Code Demystified - Part 1
QR Code Demystified - Part 2
QR Code Demystified - Part 3
QR Code Demystified - Part 4
QR Code Demystified - Part 5
QR Code Demystified - Part 6

and

http://www.thonky.com/qr-code-tutorial/introduction/

To know the Mathematics theory behind it there is a discussion in Math Stackexchange

https://math.stackexchange.com/questions/76045/reed-solomon-polynomial-generator