You cannot actually "gift" anyone one-half (or all) of your "cost basis" but, rather, the donee (receiver of the gift) generally takes your adjusted basis (a carryover basis) in the property, with certain exceptions.
Therefore, when you gifted one-half of your home to your father, the value of the gift was one-half of the fair market value on the date of the gift less one-half of any encumbrances (particularly, less one-half of your mortgage).
As a result, you most likely should have filed a gift tax return (Form 709) for the year of the gift (2012), assuming the value of the gift exceeded the annual exclusion of $15,000.
