(a) General rule Except as otherwise provided in this section, the net direct interest expense with respect to any short-term obligation shall be allowed as a deduction for the taxable year only to the extent such expense exceeds the sum of
(1) the daily portions of the acquisition discount for each day during the taxable year on which the taxpayer held such obligation, and
(2) the amount of any interest payable on the obligation (other than interest taken into account in determining the amount of the acquisition discount) which accrues during the taxable year while the taxpayer held such obligation (and is not included in the gross income of the taxpayer for such taxable year by reason of the taxpayers method of accounting).