private void ReorderData()
{
int length = viewData.Length;
int[] reversedBits = FourierHelper.ReverseBits(FourierHelper.Log2(length));
for (int i = 0; i < length; i++)
{
int swap = reversedBits[i];
if (swap > i)
{
SwapViewData(i, swap);
}
}
}
/// <summary>
/// The core transformation implementation for one dimension.
/// </summary>
/// <param name="forward">Indicates the transformation direction.</param>
protected override void TransformCore(bool forward)
{
int length = viewData.Length;
int ln = FourierHelper.Log2(length);
ReorderData();
// successive doubling
int N = 1;
for (int level = 1; level <= ln; level++)
{
int M = N;
N <<= 1;
double[] realCosine = FourierHelper.RealCosineCoefficients(level, forward);
double[] imagSine = FourierHelper.ImaginarySineCoefficients(level, forward);
for (int j = 0; j < M; j++)
{
double uR = realCosine[j];
double uI = imagSine[j];
for (int evenT = j; evenT < length; evenT += N)
{
int even = evenT << 1;
int odd = (evenT + M) << 1;
double r = viewData[odd];
double i = viewData[odd + 1];
double odduR = r * uR - i * uI;
double odduI = r * uI + i * uR;
r = viewData[even];
i = viewData[even + 1];
viewData[even] = r + odduR;
viewData[even + 1] = i + odduI;
viewData[odd] = r - odduR;
viewData[odd + 1] = i - odduI;
}
}
}
}