public void ComputeFHT(ref double[] A, int nPoints, bool enableOverlap = false)
{
kWindowSize = nPoints;
var mSineTab = FHTArrays.GetHalfSineTable(nPoints);
int i, n, n2, theta_inc;
// 1, 2 round
for (i = 0; i < nPoints; i += 4)
{
double x0 = A[i];
double x1 = A[i + 1];
double x2 = A[i + 2];
double x3 = A[i + 3];
double y0 = x0 + x1;
double y1 = x0 - x1;
double y2 = x2 + x3;
double y3 = x2 - x3;
A[i] = y0 + y2;
A[i + 2] = y0 - y2;
A[i + 1] = y1 + y3;
A[i + 3] = y1 - y3;
}
// 3 round
for (i = 0; i < nPoints; i += 8)
{
double alpha, beta;
alpha = A[i + 0];
beta = A[i + 4];
A[i + 0] = alpha + beta;
A[i + 4] = alpha - beta;
alpha = A[i + 2];
beta = A[i + 6];
A[i + 2] = alpha + beta;
A[i + 6] = alpha - beta;
alpha = A[i + 1];
double beta1 = invsqrt2 * (A[i + 5] + A[i + 7]);
double beta2 = invsqrt2 * (A[i + 5] - A[i + 7]);
A[i + 1] = alpha + beta1;
A[i + 5] = alpha - beta1;
alpha = A[i + 3];
A[i + 3] = alpha + beta2;
A[i + 7] = alpha - beta2;
}
n = 16;
n2 = 8;
theta_inc = nPoints >> 4;
while (n <= nPoints)
{
for (i = 0; i < nPoints; i += n)
{
int j;
int theta = theta_inc;
double alpha, beta;
int n4 = n2 >> 1;
alpha = A[i];
beta = A[i + n2];
A[i] = alpha + beta;
A[i + n2] = alpha - beta;
alpha = A[i + n4];
beta = A[i + n2 + n4];
A[i + n4] = alpha + beta;
A[i + n2 + n4] = alpha - beta;
for (j = 1; j < n4; j++)
{
double sinval = mSineTab[theta];
double cosval = mSineTab[theta + (nPoints >> 2)];
double alpha1 = A[i + j];
double alpha2 = A[i - j + n2];
double beta1 = A[i + j + n2] * cosval + A[i - j + n] * sinval;
double beta2 = A[i + j + n2] * sinval - A[i - j + n] * cosval;
theta += theta_inc;
A[i + j] = alpha1 + beta1;
A[i + j + n2] = alpha1 - beta1;
A[i - j + n2] = alpha2 + beta2;
A[i - j + n] = alpha2 - beta2;
}
}
n *= 2;
n2 *= 2;
theta_inc >>= 1;
}
if (!enableOverlap)
{
return;
}
OverlapSize = nPoints / kOverlapCount;
var postWindow = FHTArrays.GetPostWindow(kWindowSize);
for (i = 0; i < kWindowSize; i++)
{
A[i] *= postWindow[i];
}
overlap.AddOverlap(ref A);
}
