Bifunge

Not to be confused with Befunge, ifunge, nor Befunge/index.php.

Bifunge is a fungeoid invented by User:None1. As the name states, this esolang uses bits.

Memory

Bifunge uses a bit stack.

I/O buffer

In order to use bit I/O, Bifunge has input and output buffers. The input buffer is a big-endian byte. When it's exhausted, a new byte is read and put into the buffer. The output buffer is a big-endian byte, too. When It's full, a byte is printed and the buffer is cleared.

Commands

Every command in Bifunge is a 2x2 bit grid, so there are 16 commands. The playfield extends indefinitely on all directions.

The IP is initially on the first command in the program, and its initial direction is right.

Representation

In order to make programs more readable, implementations are allowed to use one character to represent one bit. Characters with odd ASCII values are treated as 1 while others are treated as 0.

Command list

We'll use abcd to represent the command:

ab
cd

Command table

Command	Meaning
0000	NOP
0001	Pop two bits, AND them, and push the result.
0010	Pop two bits, OR them, and push the result.
0011	Change IP direction to down.
0100	Pop two bits, XOR them, and push the result.
0101	Change IP direction to right.
0110	Pop a bit, if it's 1, change IP direction to left, otherwise right.
0111	Read a bit from the input buffer and push it.
1000	Pop a bit, NOT it, and push the result.
1001	Pop a bit, if it's 1, change IP direction to up, otherwise down.
1010	Change IP direction to left.
1011	Pop a bit, and output it to the output buffer.
1100	Change IP direction to up.
1101	Halt.
1110	Push a 0 bit onto stack.
1111	Push a 1 bit onto stack.

Computational class

It's a push-down automaton.