unsafe void decode_subframe_lpc(BitReader bitreader, FlacFrame frame, int ch)
{
// warm-up samples
int obits = frame.subframes[ch].obits;
for (int i = 0; i < frame.subframes[ch].best.order; i++)
{
frame.subframes[ch].best.residual[i] = bitreader.readbits_signed(obits);
}
// LPC coefficients
frame.subframes[ch].best.cbits = (int)bitreader.readbits(4) + 1; // lpc_precision
if (frame.subframes[ch].best.cbits >= 16)
{
throw new Exception("cbits >= 16");
}
frame.subframes[ch].best.shift = bitreader.readbits_signed(5);
if (frame.subframes[ch].best.shift < 0)
{
throw new Exception("negative shift");
}
for (int i = 0; i < frame.subframes[ch].best.order; i++)
{
frame.subframes[ch].best.coefs[i] = bitreader.readbits_signed(frame.subframes[ch].best.cbits);
}
// residual
decode_residual(bitreader, frame, ch);
}
unsafe void decode_subframe_verbatim(BitReader bitreader, FlacFrame frame, int ch)
{
int obits = frame.subframes[ch].obits;
for (int i = 0; i < frame.blocksize; i++)
{
frame.subframes[ch].best.residual[i] = bitreader.readbits_signed(obits);
}
}
unsafe void decode_subframe_fixed(BitReader bitreader, FlacFrame frame, int ch)
{
// warm-up samples
int obits = frame.subframes[ch].obits;
for (int i = 0; i < frame.subframes[ch].best.order; i++)
{
frame.subframes[ch].best.residual[i] = bitreader.readbits_signed(obits);
}
// residual
decode_residual(bitreader, frame, ch);
}
unsafe void decode_residual(BitReader bitreader, FlacFrame frame, int ch)
{
// rice-encoded block
// coding method
frame.subframes[ch].best.rc.coding_method = (int)bitreader.readbits(2); // ????? == 0
if (frame.subframes[ch].best.rc.coding_method != 0 && frame.subframes[ch].best.rc.coding_method != 1)
{
throw new Exception("unsupported residual coding");
}
// partition order
frame.subframes[ch].best.rc.porder = (int)bitreader.readbits(4);
if (frame.subframes[ch].best.rc.porder > 8)
{
throw new Exception("invalid partition order");
}
int psize = frame.blocksize >> frame.subframes[ch].best.rc.porder;
int res_cnt = psize - frame.subframes[ch].best.order;
int rice_len = 4 + frame.subframes[ch].best.rc.coding_method;
// residual
int j = frame.subframes[ch].best.order;
int *r = frame.subframes[ch].best.residual + j;
for (int p = 0; p < (1 << frame.subframes[ch].best.rc.porder); p++)
{
if (p == 1)
{
res_cnt = psize;
}
int n = Math.Min(res_cnt, frame.blocksize - j);
int k = frame.subframes[ch].best.rc.rparams[p] = (int)bitreader.readbits(rice_len);
if (k == (1 << rice_len) - 1)
{
k = frame.subframes[ch].best.rc.esc_bps[p] = (int)bitreader.readbits(5);
for (int i = n; i > 0; i--)
{
*(r++) = bitreader.readbits_signed((int)k);
}
}
else
{
bitreader.read_rice_block(n, (int)k, r);
r += n;
}
j += n;
}
}
unsafe void decode_subframe_constant(BitReader bitreader, FlacFrame frame, int ch)
{
int obits = frame.subframes[ch].obits;
frame.subframes[ch].best.residual[0] = bitreader.readbits_signed(obits);
}