public void TestFloorLog2Properties(int seed)
{
var rand = new Random(seed);
for (var sample = 0; sample < 100; ++sample)
{
var n = rand.Next() ^ (rand.Next() << 16);
if (n == 0)
{
continue;
}
var log2n = FastFourierTransform.FloorLog2(n);
var hibit = 1 << log2n;
var mask = hibit | (hibit - 1);
Assert.AreEqual(0, n & ~mask, "higher bits");
Assert.AreEqual(hibit, n & hibit, "high bit");
}
}
private static float[] GenerateCloudFft(int dx, int dy, int dz)
{
var log2X = (byte)FastFourierTransform.FloorLog2(dx);
var log2Y = (byte)FastFourierTransform.FloorLog2(dy);
var log2Z = (byte)FastFourierTransform.FloorLog2(dz);
Trace.WriteLine($"Generate random {dx} x {dy} x {dz} data...");
var data = new Complex[dx * dy * dz];
var rand = new Random(101);
for (var i = 0; i < data.Length; ++i)
{
data[i] = rand.NextDouble();
}
Trace.WriteLine($"Compute multi-dimensional FFT...");
data.MultiFft(log2X, log2Y, log2Z);
Trace.WriteLine($"Apply 1/f^2 scaling...");
var p = 0;
for (var x = 0; x < dx; ++x)
{
var fx = Math.Min(x, dx - x);
for (var y = 0; y < dy; ++y)
{
var fy = Math.Min(y, dy - y);
for (var z = 0; z < dz; ++z)
{
var fz = Math.Min(z, dz - z);
var ff = fx * fx + fy * fy + fz * fz;
if (ff == 0)
{
data[p++] = 0;
}
else
{
data[p++] /= ff;
}
}
}
}
Trace.WriteLine("Compute inverse multi-dimensional FFT...");
data.InverseMultiFft(log2X, log2Y, log2Z);
Trace.WriteLine("Convert complex real component to normalized float...");
var minc = data.Min(x => x.Real);
var maxc = data.Max(x => x.Real);
var result = new float[data.Length];
for (var i = 0; i < data.Length; ++i)
{
result[i] = (float)((data[i].Real - minc) / (maxc - minc));
}
Trace.WriteLine($"max( abs( R ) ) = {data.Max( c => Math.Abs( c.Real ) )}");
Trace.WriteLine($"max( abs( I ) ) = {data.Max( c => Math.Abs( c.Imaginary ) )}");
return(result);
}
public void TestFloorLog2(int n, int expect)
{
Assert.AreEqual(expect, FastFourierTransform.FloorLog2(n));
}
