If a shareholder in a corporation receives its stock or rights to acquire its stock (referred to in this subsection as “new stock”) in a distribution to which section
305
(a) applies, then the basis of such new stock and of the stock with respect to which it is distributed (referred to in this section as “old stock”), respectively, shall, in the shareholder’s hands, be determined by allocating between the old stock and the new stock the adjusted basis of the old stock. Such allocation shall be made under regulations prescribed by the Secretary.