Function dft_1d_step

tests/validation/reference/DFT.cpp:82–106

 */
template <typename T>
void dft_1d_step(const T *src_ptr, T *dst_ptr, size_t N)
{
#if defined(_OPENMP)
#pragma omp parallel for
#endif /* _OPENMP */
    for (unsigned int k = 0; k < N; ++k)
    {
        float Xr = 0;
        float Xi = 0;
        for (unsigned int n = 0; n < N; ++n)
        {
            const float alpha     = (2 * M_PI * k * n) / N;
            const float val_r     = src_ptr[2 * n];
            const float val_i     = src_ptr[2 * n + 1];
            const float cos_alpha = cos(alpha);
            const float sin_alpha = sin(alpha);

            Xr += val_r * cos_alpha + val_i * sin_alpha;
            Xi += val_i * cos_alpha - val_r * sin_alpha;
        }

        dst_ptr[k * 2]     = Xr;
        dst_ptr[k * 2 + 1] = Xi;
    }
}

/** Performs an one dimensional inverse DFT on a given real sequence.
 *