private static Mdct GetSetup(int n)
{
lock (_setupCache)
{
if (!_setupCache.ContainsKey(n))
{
_setupCache[n] = new Mdct(n);
}
return(_setupCache[n]);
}
}
private void DecodePacket()
{
// inverse coupling
var steps = _mode.Mapping.CouplingSteps;
var halfSizeW = _mode.BlockSize / 2;
for (var i = steps.Length - 1; i >= 0; i--)
{
if (_floorData[steps[i].Angle].ExecuteChannel || _floorData[steps[i].Magnitude].ExecuteChannel)
{
var magnitude = _residue[steps[i].Magnitude];
var angle = _residue[steps[i].Angle];
// we only have to do the first half; MDCT ignores the last half
for (var j = 0; j < halfSizeW; j++)
{
float newM, newA;
if (magnitude[j] > 0)
{
if (angle[j] > 0)
{
newM = magnitude[j];
newA = magnitude[j] - angle[j];
}
else
{
newA = magnitude[j];
newM = magnitude[j] + angle[j];
}
}
else
{
if (angle[j] > 0)
{
newM = magnitude[j];
newA = magnitude[j] + angle[j];
}
else
{
newA = magnitude[j];
newM = magnitude[j] - angle[j];
}
}
magnitude[j] = newM;
angle[j] = newA;
}
}
}
// apply floor / dot product / MDCT (only run if we have sound energy in that channel)
for (var c = 0; c < _channels; c++)
{
var floorData = _floorData[c];
var res = _residue[c];
if (floorData.ExecuteChannel)
{
_mode.Mapping.ChannelSubmap[c].Floor.Apply(floorData, res);
Mdct.Reverse(res, _mode.BlockSize);
}
else
{
// since we aren't doing the IMDCT, we have to explicitly clear the back half of the block
Array.Clear(res, halfSizeW, halfSizeW);
}
}
}