Day 4

Math

	Today is going to be all about the math instructions ADD and SUB.

The ADD Instruction
	Now, reel in the fish slowly! Oops, ADD means ADDition, not Attension Deficit Disorder!
What was I thinking!.

	Ok, now that the bad joke is out of the way, ADD works like this:
		ADD t1,t2,t3  ; t1 = t2 + t3; is just about the simplest way I can describe it.

	I've also seen:
		ADD t1, 2 ; which is supposed to be t1 += 2, appearantly. THIS DOESN'T ALWAYS WORK!
		; alot of the time, an assembler either errors or interprets this as t1 += V0
	
	Which brings me to another point, a register's (in some assemblers) number can be used
instead it it's t1,v0,a3 style name. See Nemu's debugger for as far as I know, is the correct order.

The SUB Instruction
	INSERT BAD JOKE ABOUT SubWay HERE.

	The SUB Instruction works like so:
		SUB t0,t4,t5 ; t0 = t4 - t5; There's a chance I might have t4 and t5 in the wrong order,
		; but I think I have it right.

	The "I've also seen" comment applies to SUB as well.

The MUL/DIV Instruction
	The MUL and DIV Instructions work like this (as far as I can tell):

		MUL t0,t2,t4 ; t0 = t2 * t4;

		DIV t1,t0,t6 ; t1 = t0 / t6;

	Also note that all these math instructions use signed numbers.

Comparison/Branch Instructions
	This would have been shorter than I wanted it to be, so I'll have to talk about Comparison/Branch Instructions
also.

	The first instruction we'll learn is BNEZ, BNEZ is a psuedo-instruction that only Anarko's assembler doesn't
support (along with LA). BNEZ is used like so:

	bnez t1, LABEL ; IF t1 not equal zero THEN GOTO LABEL

For assemblers that don't support it, use:

	bne t1,$0,LABEL ; same as above, note that $0 is the special CPU register that is permanently zero.

The other use for BNE (no Z) is:

	bne t1,t3,LABEL ; IF t1 not equal t3 THEN GOTO LABEL

There is also:

	beq t1,t3,LABEL ; IF t1 == t3 THEN GOTO LABEL

	blt t0,t1,LABEL ; IF t0 less than t1 THEN GOTO LABEL

	bgt t0,t1,LABEL ; IF t0 greater then t1 THEN GOTO LABEL

	ble t2,t4,LABEL ; IF t2 less or = to t4 THEN GOTO LABEL

	bge t2,t4,LABEL ; IF t2 greater or = to t4 THEN GOTO LABEL

Add a U to the end of the instruction (like BGEU) to compare unsigned numbers.

This Day In Review

	Tomorrow, we'll either learn another set of instructions, or we'll do
something else (maybe a pic on screen)!

	Until Next Time!,
		- Mike H a.k.a GbaGuy

Intro - Day 5