Calculates the inverse discrete cosine transform (DCT) of a Vec and writes the results in the calling vector. If Vec Length is a power of 2, the function uses an efficient algorithm that is significantly faster than the direct computation of DCT. For other values of Vec length, this function uses the direct formulas given below; however, the symmetry of cosine function is taken into account, which allows to perform about half of the multiplication operations in the formulas. In the following definition of inverse DCT, N=Vec.Length and V is the calling vector: 

DCT

IDCT Method