/*
* MIPS-Stimulator : branch.js [Branch submodule for VM]
* Copyright (C) 2017 Progyan Bhattacharya, Bytes Club
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
"use strict";
/** function: branch
* @desc Performs Branch and Jump Operation Inside Virtual Machine
* @param {Object} item - Operand Details and Arguments
* @param {Number} i - Index of The Instrcution
*/
const branch = function (item, i) {
switch (item.type) {
case "Equality": case "Inequality": case "Greater": case "Lesser": {
const [ lreg, rreg, label ] = item.argument;
const lval = this.valueFromRegister(lreg, i);
const rval = this.valueFromRegister(rreg, i);
const target = this.valueFromLabel(label, i);
switch (item.type) {
case "Equality": {
if (lval === rval) {
this.updatePC(target);
}
break;
}
case "Inequality": {
if (lval !== rval) {
this.updatePC(target);
}
break;
}
case "Greater": {
if (lval > rval) {
this.updatePC(target);
}
break;
}
case "Lesser": {
if (lval < rval) {
this.updatePC(target);
}
break;
}
default: return;
}
break;
}
case "EqualtoZero": {
const [ lreg, label ] = item.argument;
const lval = this.valueFromRegister(lreg, i);
const target = this.valueFromLabel(label, i);
if (lval === 0) {
this.updatePC(target);
}
break;
}
case "InequaltoZero": {
const [ lreg, label ] = item.argument;
const lval = this.valueFromRegister(lreg, i);
const target = this.valueFromLabel(label, i);
if (lval !== 0) {
this.updatePC(target);
}
break;
}
case "JumpReg": {
const [ labelReg ] = item.argument;
const target = this.valueFromRegister(labelReg, i);
this.updatePC(target);
break;
}
case "Jump": {
const [ label ] = item.argument;
const target = this.valueFromLabel(label, i);
this.updatePC(target);
break;
}
default:
console.error(`Error: Invalid branch statement found at ${i}`);
process.exit(4);
}
};
module.exports = branch;