I have the following block of code to update order totals when either one of two classes change. Can someone show me how I can split this into a function so I can call the same code under other circumstances?

$('.update-subtotal input.number').change(function(){

if (!$(this).hasClass('quantity')) $(this).val(($(this).val()*1).toFixed(2));

var parent = $(this).parents('.update-subtotal:first');

var quantity = $(parent).find('input.quantity').val();

var lineprice = $(parent).find('input.lineprice').val();

var target = $(parent).find('input.subtotal:first');

var value = (quantity*lineprice).toFixed(2);

$(target).val(value);

var subtotal = 0;

$('input.subtotal').each(function(){

var value = ($(this).val()*1);

subtotal += value;

});

var discount = $('#discount').val();

discount = discount * 1;

var type = $('#discount_type').val();

if (type == "p") {

if (discount > 100) {

$('#discount').val("100");

discount = 100;

}

discount = (discount / 100) * subtotal;

$('#discount_percent').html("%");

} else {

$('#discount_percent').html("");

}

$('#subtotal').val(subtotal.toFixed(2));

var shipping = $('#shipping').val();

var tax = 0;

$('.update-subtotal input.tax').each(function(){

var tax_amount = $(this).val();

tax += tax_amount*1;

});

var total = subtotal*1 - discount + shipping*1 + tax*1;

$('#total_tax').val(tax.toFixed(2));

$('#total').val(total.toFixed(2));

});