Magento – Modify Shopping Cart Rules Function to apply discounts by Percentage of Original Price Instead of Product Price Discount

I'm working on a project where the entire store products have a special price different (lowered) from the original price.

I want to be able to apply shopping cart discounts By Percentage of the Original Price just like Catalog Discount Price Rules does.

Right now, if I apply a shopping cart “Percentage of product price discount” rule, it will apply the discount to the special price instead of the original price.

Where is the function for Shopping Cart Rules at? Any details on modifying it to apply discounts on original price will be appreciated.