Math routines.

Summary

Multiply 2 unsigned bytes.

_al	first operand.
_bl	second operand.

_cx	16 bits unsigned result.

Divide 2 unsigned bytes.

_al	Dividend.
_bl	Divisor.

_cl	Result (_al / _bl).
_dl	Remainder (_al mod _bl).

Multiply 2 unsigned words.

Return _cx - result bytes 0 and 1. _dx - result bytes 2 and 3.