Section 11-619. Computation of net income

The net income shall be computed
  in accordance with  the  method  of  accounting  regularly  employed  in
  keeping  the books of such taxpayer; but if no such method of accounting
  has been so employed, or if the method employed does not clearly reflect
  the income, the computation shall be made upon such basis  and  in  such
  manner  as  in  the  opinion of the commissioner of finance does clearly
  reflect the income. In determining net income, war losses,  taxation  of
  property   recovered,   and  basis  of  property  shall  be  treated  in
  substantially the same manner as such losses, recoveries and  basis  are
  treated  under  the  applicable  provisions  of section thirteen hundred
  thirty-one of the internal revenue code.