protected static bool GetCRC(
MpegFrame frame, int[] rateTable, int[][] allocLookupTable, bool readScfsiBits, ref uint crc)
{
// ugh... we basically have to re-implement the allocation logic here.
// keep up with how many active subbands we need to read selection info for
var scfsiBits = 0;
// only read as many subbands as we actually need; pay attention to the intensity stereo subbands
var subbandCount = rateTable.Length;
var jsbound = subbandCount;
if (frame.ChannelMode == MpegChannelMode.JointStereo)
{
jsbound = frame.ChannelModeExtension * 4 + 4;
}
// read the full stereo subbands
var channels = frame.ChannelMode == MpegChannelMode.Mono ? 1 : 2;
var sb = 0;
for (; sb < jsbound; sb++)
{
var bits = allocLookupTable[rateTable[sb]][0];
for (int ch = 0; ch < channels; ch++)
{
var alloc = frame.ReadBits(bits);
if (alloc > 0)
{
scfsiBits += 2;
}
MpegFrame.UpdateCRC(alloc, bits, ref crc);
}
}
// read the intensity stereo subbands
for (; sb < subbandCount; sb++)
{
var bits = allocLookupTable[rateTable[sb]][0];
var alloc = frame.ReadBits(bits);
if (alloc > 0)
{
scfsiBits += channels * 2;
}
MpegFrame.UpdateCRC(alloc, bits, ref crc);
}
// finally, read the scalefac selection bits
if (readScfsiBits)
{
while (scfsiBits >= 2)
{
MpegFrame.UpdateCRC(frame.ReadBits(2), 2, ref crc);
scfsiBits -= 2;
}
}
return(true);
}
