attiny - Does anyone have code to emulate a 16-bit input shift register with an ATtiny2313?

I would like to use an ATtiny2313 to emulate a Super Nintendo controller because I have an ATtiny2313 but I do not have an input shift register and I don't feel like soldering wires onto an existing SNES controller board.

This application requires 12 inputs (bits 13-16 are always 1) and a latch, clock, and data out pin.

Do you have this code lying around? It can't be more than 20 instructions.

Answer

There's already an 8-bit shift register built into the Universal Serial Interface (USI). All you have to do is use it twice in a row.