Procedurality.Channel.fastFourierTransform C# (CSharp) Method

		private void fastFourierTransform(float[] data, int size, int isign) {
			int i1, i2, i3;
			int i2rev, i3rev, ip1, ip2, ip3, ifp1, ifp2;
			int ibit, idim, k1, k2, n, nprev, nrem, ntot;
			float tempi, tempr;
			float theta, wi, wpi, wpr, wr, wtemp;
			ntot = size*size;
			nprev = 1;
			for (idim = 2; idim >= 1; idim--) {
				n = size;
				nrem = ntot / (n * nprev);
				ip1 = nprev << 1;
				ip2 = ip1 * n;
				ip3 = ip2 * nrem;
				i2rev = 1;
				for (i2 = 1; i2 <= ip2; i2 += ip1) {
					if (i2 < i2rev) {
						for (i1 = i2; i1 <= i2 + ip1 - 2; i1 += 2) {
							for (i3 = i1; i3 <= ip3; i3 += ip2) {
								i3rev = i2rev + i3 - i2;
								tempr=data[i3]; data[i3] = (data[i3rev]); data[i3rev] = tempr;
								tempr=data[i3 + 1]; data[i3 + 1] = data[i3rev + 1]; data[i3rev + 1] = tempr;
							}
						}
					}
					ibit = ip2 >> 1;
					while (ibit >= ip1 && i2rev > ibit) {
						i2rev -= ibit;
						ibit >>= 1;
					}
					i2rev += ibit;
				}
				ifp1 = ip1;
				while (ifp1 < ip2) {
					ifp2 = ifp1 << 1;
					theta = isign * ((float)Math.PI * 2) / (ifp2 / ip1);
					wtemp = (float)Math.Sin(0.5 * theta);
					wpr = -2.0f * wtemp * wtemp;
					wpi = (float)Math.Sin(theta);
					wr = 1.0f;
					wi = 0.0f;
					for (i3 = 1; i3 <= ifp1; i3 += ip1) {
						for (i1 = i3; i1 <= i3 + ip1 - 2; i1 += 2) {
							for (i2 = i1; i2 <= ip3; i2 += ifp2) {
								k1 = i2;
								k2 = k1 + ifp1;
								tempr = wr * data[k2] - wi * data[k2 + 1];
								tempi = wr * data[k2 + 1] + wi * data[k2];
								data[k2] = data[k1] - tempr;
								data[k2 + 1] = data[k1 + 1] - tempi;
								data[k1] += tempr;
								data[k1 + 1] += tempi;
							}
						}
						wr = (wtemp = wr) * wpr - wi * wpi + wr;
						wi = wi * wpr + wtemp * wpi + wi;
					}
					ifp1 = ifp2;
				}
				nprev *= n;
			}
		}