cadencii.fft.rdft C# (CSharp) Method

        public static void rdft( int n, int isgn, double* a, int* ip, double* w ) {
            int nw, nc;
            double xi;

            nw = ip[0];
            if ( n > (nw << 2) ) {
                nw = n >> 2;
                makewt( nw, ip, w );
            }
            nc = ip[1];
            if ( n > (nc << 2) ) {
                nc = n >> 2;
                makect( nc, ip, w + nw );
            }
            if ( isgn >= 0 ) {
                if ( n > 4 ) {
                    cftfsub( n, a, ip, nw, w );
                    rftfsub( n, a, nc, w + nw );
                } else if ( n == 4 ) {
                    cftfsub( n, a, ip, nw, w );
                }
                xi = a[0] - a[1];
                a[0] += a[1];
                a[1] = xi;
            } else {
                a[1] = 0.5 * (a[0] - a[1]);
                a[0] -= a[1];
                if ( n > 4 ) {
                    rftbsub( n, a, nc, w + nw );
                    cftbsub( n, a, ip, nw, w );
                } else if ( n == 4 ) {
                    cftbsub( n, a, ip, nw, w );
                }
            }
        }