lvm.js


var OP_MOVE = 0;
var OP_LOADK = 1;
var OP_LOADNIL = 3;
var OP_GETGLOBAL = 5;
var OP_SETGLOBAL = 7;
var OP_CALL = 28;
var OP_RETURN = 30;

var debugMode = false;

function LValue(type, value)
{
	this.type = type||"nil";
	this.value = value||null;
}

LValue.prototype = {
	call: function (args)
	{
		if(this.type == "function")
			return this.value;
		else
			throw "Attempt to call a " + this.type + " value";
	},
	index: function (key)
	{
		if(this.type == "table")
		{
			var val = this.value[key.value];
			if(typeof(val) == "undefined")
				return new LValue("nil", null);
			return val;
		}
		else
			throw "Attempt to index a " + this.type + " value";
	},
	setIndex: function (key, value)
	{
		if(this.type == "table")
		{
			this.value[key.value] = value;
		}
		else
			throw "Attempt to index a " + this.type + " value";
	}
};

function LValueFromString(string)
{
	return new LValue("string", string);
}

function LValueFromFunction(func)
{
	return new LValue("function", func);
}

function LBinaryChunk(chunk)
{
	this.chunk = chunk;
	this.pos = 12;
	
	this.sourceName = this.readString();
	this.lineDefined = this.readInt();
	this.lastLineDefined = this.readInt();
	this.numUpvalues = this.readByte();
	this.numParameters = this.readByte();
	this.isVararg = this.readByte();
	this.maxStackSize = this.readByte();
	
	this.instructions = [];
	
	this.numInstructions = this.readInt();
	for(var i=0;i<this.numInstructions;i++)
	{
		var ins = this.readInt();
		this.instructions.push([
			ins&0x3F, // Opcode
			(ins>>6)&0xFF, // Field A
			(ins>>23)&0x1FF, // Field B
			(ins>>14)&0x1FF // Field C
		]);
		if(debugMode)
		{
			var pi = this.instructions[this.instructions.length-1];
			sys.puts("Pos: "+(this.pos-4)+" Ins: "+ins+" OP: "+INS_OPCODE(pi)+" A: "+INS_A(pi)+" B: "+INS_B(pi)+" C: "+INS_C(pi)+" Bx: "+INS_Bx(pi));
		}
	}
	
	this.constants = [];
	
	this.numConstants = this.readInt();
	for(var i=0;i<this.numConstants;i++)
	{
		var type = this.readByte();
		switch(type)
		{
		case 0: // Nil
			this.constants.push(new LValue("nil", null));
			break;
		case 1: // Boolean
			this.constants.push(new LValue("boolean", this.readByte()));
			break;
		case 3: // Number
			this.constants.push(new LValue("number", this.readNumber()));
			break;
		case 4: // String
			this.constants.push(LValueFromString(this.readString()));
			break;
		default:
			throw "Invalid constant type "+type+" in bytecode";
		}
	}
	
	return this;
}

LBinaryChunk.prototype = {
	readBytes: function (n)
	{
		return this.chunk.slice(this.pos, this.pos+=n);
	},
	readByte: function ()
	{
		return this.readBytes(1).charCodeAt(0);
	},
	readInt: function ()
	{
		//FIXME: Endianness
		return this.readByte() | (this.readByte()<<8)
			| (this.readByte()<<16) | (this.readByte()<<24);
	},
	readString: function ()
	{
		var len = this.readInt();
		return this.readBytes(len).substring(0,len-1);
	},
	readNumber: function ()
	{
		//FIXME: Endianness
		var bytes = [this.readByte(),this.readByte(),this.readByte(),this.readByte(),
		             this.readByte(),this.readByte(),this.readByte(),this.readByte()].reverse();
		
		var sign = (bytes[0]>>7)&0x1;
		var exp = (bytes[0]&0x7F)<<4 | (bytes[1]&0xf0)>>4;
		
		var frac = ((bytes[1] & 0x0f) * Math.pow(2,48))
		          + (bytes[2] * Math.pow(2,40))
		          + (bytes[3] * Math.pow(2,32))
		          + (bytes[4] * Math.pow(2,24))
		          + (bytes[5] * Math.pow(2,16))
		          + (bytes[6] * Math.pow(2,8))
		          +  bytes[7];
		
		if(exp != 0x000 && exp != 0x7FF)
		{
			var n = (sign==1?-1:1)*Math.pow(2,exp-1023)*(1+(frac/0x10000000000000));
			return n;
		}
		else if(exp == 0x000)
		{
			return sign*0;
		}
		else
			return frac==0?sign*Infinity:NaN;
	}
};

function INS_OPCODE(ins)
{
	return ins[0];
}

function INS_A(ins)
{
	return ins[1];
}

function INS_B(ins)
{
	return ins[2];
}

function INS_C(ins)
{
	return ins[3];
}

function INS_Bx(ins)
{
	return ((INS_C(ins))|(INS_B(ins)<<9));
}

function INS_sBx(ins)
{
	return INS_Bx(ins)+0x1FFFE;
}

function LFunction(chunk, env)
{
	function F() {};
	F.prototype = chunk;
	var o = new F();
	o.environment = env;
	return o;
}

function LVM()
{
	this.callstack = [];
	this.stack = [];
	return this;
}

LVM.prototype = {
	run: function (lfFunction)
	{
		this.frame = {f:lfFunction,pc:0,reg:[]};
		this.callstack.push(this.frame);
		var instruction;
		while(this.callstack.length>0)
		{
			instruction = this.frame.f.instructions[this.frame.pc++];
			if(debugMode)
			{
				sys.puts("PC: "+(this.frame.pc-1)+" OP: "+instruction[0]);
				sys.puts("STACK: "+JSON.stringify(this.frame.reg));
			}
			switch(INS_OPCODE(instruction))
			{
			case OP_MOVE:
				this.frame.reg[INS_A(instruction)] = this.frame.reg[INS_B(instruction)];
				break;
			case OP_LOADNIL:
				for(var i = INS_A(instruction);i<=INS_B(instruction);i++)
					this.frame.reg[i] = new LValue("nil", null);
				break;
			case OP_GETGLOBAL:
				var name = this.frame.f.constants[INS_Bx(instruction)];
				this.frame.reg[INS_A(instruction)] = this.frame.f.environment.index(name);
				break;
			case OP_SETGLOBAL:
				var name = this.frame.f.constants[INS_Bx(instruction)];
				this.frame.f.environment.setIndex(name, this.frame.reg[instruction[1]]);
				break;
			case OP_LOADK:
				var value = this.frame.f.constants[INS_Bx(instruction)];
				this.frame.reg[INS_A(instruction)] = value;
				break;
			case OP_CALL:
				var f = this.frame.reg[INS_A(instruction)].call(); // return JS or LValue
				var args = this.frame.reg.slice(INS_A(instruction)+1, INS_A(instruction)+(INS_B(instruction)));
				if(typeof(f) == "function")
				{
					// JS native function
					var ret = f.apply(null, args.map(function (a) { return a.value; }));
				}
				else
				{
					// Lua function
				}
				break;
			case OP_RETURN:
				this.callstack.pop();
				break;
			default:
				throw "Unhandled opcode: "+INS_OPCODE(instruction);
			}
		}
	}
};

var testvm = new LVM();

var fs=require("fs");
var sys=require("sys");
var c = new LBinaryChunk(fs.readFileSync("luac.out", "binary"));

var default_environment = new LValue("table", {});

var print;
if(typeof(document) == "object")
	print = function (a) { document.write(a+"<br/>") }; // Browser
else
	print = require("sys").puts; // Nodejs

default_environment.setIndex(LValueFromString("print"), LValueFromFunction(print));

var f = new LFunction(c, default_environment);

try{
	testvm.run(f);
}
catch(e)
{
	print("Error: " + e);
}