/// <summary>
/// Compute a 1D fast Fourier transform of a dataset of complex numbers (as pairs of float's).
/// </summary>
/// <param name="data"></param>
/// <param name="length"></param>
/// <param name="direction"></param>
public static void FFT_Quick(float[] data, int length, FourierDirection direction)
{
/*Debug.Assert( data != null );
* Debug.Assert( data.Length >= length*2 );
* Debug.Assert( Fourier.IsPowerOf2( length ) == true );
*
* Fourier.SyncLookupTableLength( length );*/
int ln = Fourier.Log2(length);
// reorder array
Fourier.ReorderArray(data);
// successive doubling
int N = 1;
int signIndex = (direction == FourierDirection.Forward) ? 0 : 1;
for (int level = 1; level <= ln; level++)
{
int M = N;
N <<= 1;
float[] uRLookup = _uRLookupF[level, signIndex];
float[] uILookup = _uILookupF[level, signIndex];
for (int j = 0; j < M; j++)
{
float uR = uRLookup[j];
float uI = uILookup[j];
for (int evenT = j; evenT < length; evenT += N)
{
int even = evenT << 1;
int odd = (evenT + M) << 1;
float r = data[odd];
float i = data[odd + 1];
float odduR = r * uR - i * uI;
float odduI = r * uI + i * uR;
r = data[even];
i = data[even + 1];
data[even] = r + odduR;
data[even + 1] = i + odduI;
data[odd] = r - odduR;
data[odd + 1] = i - odduI;
}
}
}
}
static private void ReorderArray(double[] data)
{
Debug.Assert(data != null);
int length = data.Length / 2;
Debug.Assert(Fourier.IsPowerOf2(length) == true);
Debug.Assert(length >= cMinLength);
Debug.Assert(length <= cMaxLength);
int[] reversedBits = Fourier.GetReversedBits(Fourier.Log2(length));
for (int i = 0; i < length; i++)
{
int swap = reversedBits[i];
if (swap > i)
{
Fourier.Swap(ref data[i << 1], ref data[swap << 1]);
Fourier.Swap(ref data[i << 1 + 1], ref data[swap << 1 + 1]);
}
}
}