notes.txt

Calling mcode words
===================

We need to be able to call mcode words from Forth and other mcode words.

Each mcode word starts with a short wrapper:

	CALL mc
	jp (iy) ; returns to Forth interpreter
mc: ... machine code routine here ...
	ret

Forth code calls the mcode word using its compilation address, which points to the mcode wrapper. 

Machine code can bypass the wrapper and call the 'mc' routine directly. The machine code address of a word can be found by adding 7 to the compilation address of the word.


Short forward jumps
===================

Currently mcode versions of IF, ELSE and GOTO emit long forward jumps using the JP or JP Z instructions. These could be optimized to short branches, but this is fairly compilated, so it has not been done to keep the compiler simple.

This would either require multiple passes or rewinding the parser.

Multiple passes: 1st pass records which jumps can be shortened, 2nd pass generates the code.

Rewinding the parser: assume either long or short jump. If we guessed wrong, rewind the parser and undo generated code since the beginning of jump.