javascript数值精确计算

/**
* The function for decimal's add, subtract, multiplication, division. Not get the float result.
 * And add the function to Number's prototype, so you can use it as:
 * var result = dcmAdd(0.2,0.1); //or var result = (0.2).add(0.1);
 * */
function floatAdd(arg1, arg2) {
	var r1, r2, m, n;
	try {
		r1 = arg1.toString().split(".")[1].length
	} catch (e) {
		r1 = 0
	}
	try {
		r2 = arg2.toString().split(".")[1].length
	} catch (e) {
		r2 = 0
	}
	n = Math.max(r1, r2); // （不加这个还是有问题，如68.04+16.17，因为在下面的arg1*m时会出现浮点数，
	m = Math.pow(10, n);
	// 当然也可以用dcmMul(arg1,m)来解决，但考虑到效率还是加这个吧。）
	return ((arg1 * m + arg2 * m) / m).toFixed(n);
}

function floatSbt(arg1, arg2) {
	var r1, r2, m, n;
	try {
		r1 = arg1.toString().split(".")[1].length
	} catch (e) {
		r1 = 0
	}
	try {
		r2 = arg2.toString().split(".")[1].length
	} catch (e) {
		r2 = 0
	}
	n = Math.max(r1, r2);// （不加这个还是有问题，如68.04-16.17）
	m = Math.pow(10, n);
	return ((arg1 * m - arg2 * m) / m).toFixed(n);
}

function floatMul(arg1, arg2) {
	var m = 0, s1 = arg1.toString(), s2 = arg2.toString();
	try {
		m += s1.split(".")[1].length
	} catch (e) {
	}
	try {
		m += s2.split(".")[1].length
	} catch (e) {
	}
	return Number(s1.replace(".", "")) * Number(s2.replace(".", "")) / Math.pow(10, m);
}

function floatDiv(arg1, arg2) {
	var t1 = 0, t2 = 0, r1, r2;
	try {
		t1 = arg1.toString().split(".")[1].length
	} catch (e) {
	}
	try {
		t2 = arg2.toString().split(".")[1].length
	} catch (e) {
	}
	r1 = Number(arg1.toString().replace(".", ""));
	r2 = Number(arg2.toString().replace(".", ""));
	return (r1 / r2) * Math.pow(10, t2 - t1);
};

Number.prototype.succ = function() {
	return this + 1;
},

Number.prototype.add = function(arg) {
	return floatAdd(this, arg);
},

Number.prototype.sub = function(arg) {
	return floatSbt(this, arg);
},

Number.prototype.mul = function(arg) {
	return floatMul(this, arg);
},

Number.prototype.div = function(arg) {
	return floatDiv(this, arg);
}
Number.prototype.succ = function() {
	return this + 1;
},

String.prototype.add = function(arg) {
	return floatAdd(this, arg);
},

String.prototype.sub = function(arg) {
	return floatSbt(this, arg);
},

String.prototype.mul = function(arg) {
	return floatMul(this, arg);
},

String.prototype.div = function(arg) {
	return floatDiv(this, arg);
}