Add more 8086 Instructions

[roerohan]

Add more Instructions

Currently, 8086.js can only execute the instructions in the switch-case below. However, support needs to be added for the remaining instructions to make it more usable.

Also, some instructions are not implemented properly, which maybe be because of one of the following reasons.

• They do not set the right flags
• They do not check the operand sizes before executing the operation.

These need to be fixed to make it behave more like an Intel 8086.

Currently implemented instructions

The following is a list of instructions that have been implemented. They have been written in src/emulator/cpu/core.js, and they use the Addressing class from addressing.js in the same folder.

Note: Relative addressing has not been implemented yet.

8086.js/src/emulator/cpu/core.js

Lines 33 to 172 in 017505b

	switch (mnemonic.value) {
	case 'MOV':
	if (op1.size < op2.size) {
	throw SyntaxError(`Can't move larger ${op2.size} bit value to ${op1.size} bit location`);
	}
	setAddr(op1, getAddr(op2));
	break;
	case 'JS':
	if (regs.flags.getFlag(flags.sign) === 1) {
	ip = getAddr(op1) - 1;
	}
	break;
	case 'JNS': {
	if (regs.flags.getFlag(flags.sign) === 0) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'JO': {
	if (regs.flags.getFlag(flags.overflow) === 1) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'JNO': {
	if (regs.flags.getFlag(flags.overflow) === 0) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'JP':
	case 'JPE':
	{
	if (regs.flags.getFlag(flags.parity) === 1) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'JNP':
	{
	if (regs.flags.getFlag(flags.parity) === 0) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'ADD':
	if (!op2) {
	let s = op1.size === 8 ? regs.AX.get('l') : regs.AX.get();
	s += getAddr(op1);
	regs.AX.set(s);
	} else {
	let s = getAddr(op1);
	s += getAddr(op2);
	setAddr(op1, s);
	}
	break;
	case 'DIV':
	if (op1.size === 8) {
	const al = regs.AX.get('l') / getAddr(op1);
	const ah = regs.AX.get('l') % getAddr(op1);
	regs.AX.set(al, 'l');
	regs.AX.set(ah, 'h');
	} else {
	const ax = regs.AX.get() / getAddr(op1);
	const dx = regs.AX.get() % getAddr(op1);
	regs.AX.set(ax);
	regs.DX.set(dx);
	}
	break;
	case 'MUL':
	if (op1.size === 8) {
	const prod = regs.AX.get('l') * getAddr(op1);
	regs.AX.set(prod);
	} else {
	const prod = regs.AX.get() * getAddr(op1);
	regs.AX.set(prod);
	// Store higher bits in DX
	}
	break;
	case 'AND':
	setAddr(op1, getAddr(op1) & getAddr(op2));
	break;
	case 'OR':
	setAddr(op1, getAddr(op1) | getAddr(op2));
	break;
	case 'SUB': {
	const s1 = getAddr(op1);
	const s2 = getAddr(op2);
	const ans = s1 - s2;
	setAddr(op1, ans);
	break;
	}
	case 'CMP': {
	const s1 = getAddr(op1);
	const s2 = getAddr(op2);
	if (s1 === s2) {
	regs.flags.setFlag(flags.zero);
	regs.flags.unsetFlag(flags.carry);
	} else if (s1 > s2) {
	regs.flags.unsetFlag(flags.zero);
	regs.flags.unsetFlag(flags.carry);
	} else {
	regs.flags.setFlag(flags.carry);
	regs.flags.unsetFlag(flags.zero);
	}
	break;
	}
	case 'NOT': {
	setAddr(op1, ~getAddr(op1));
	break;
	}
	case 'JMP': {
	ip = getAddr(op1) - 1;
	break;
	}
	case 'JE':
	case 'JZ':
	{
	if (regs.flags.getFlag(flags.zero) === 1) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	case 'JNE':
	case 'JNZ':
	{
	if (regs.flags.getFlag(flags.zero) === 0) {
	ip = getAddr(op1) - 1;
	}
	break;
	}
	default:
	break;
	}

[gieitlaldywithamy]

i'll take this if you want looks like a decent first issue :)

[roerohan]

That would be wonderful @gieitlaldywithamy 😄 🎉
I'll assign this issue to you, you can add support for any number of instructions you want and make a PR.
However, I plan to keep this issue open until we can support all Intel 8086 instructions!

Please check out CONTRIBUTING.md for guidelines about commit messages and code style

[gieitlaldywithamy]

thanks for the git tips but could you provide some more specifications? what instructions do you want implemented and which don't work? is this the list you would like implemented
https://en.wikipedia.org/wiki/X86_instruction_listings

[thebongy]

@gieitlaldywithamy We usually use
https://www.gabrielececchetti.it/Teaching/CalcolatoriElettronici/Docs/i8086_instruction_set.pdf as a reference.

The pdf sometimes doesn't describe how flag registers are set for some commands. For those cases, I recommend searching up the instruction on google, and trying to research more about a specific instruction, so we can accurately mimic how it would work on an 8086.