void DoHuffmanEncoding(Int16[] DU, ref Int16 DC, Tables.BitString[] HTDC, Tables.BitString[] HTAC, BinaryWriter bw)
{
Tables.BitString EOB = HTAC[0x00];
Tables.BitString M16zeroes = HTAC[0xF0];
Byte i;
Byte startpos;
Byte end0pos;
Byte nrzeroes;
Byte nrmarker;
Int16 Diff;
// Encode DC
Diff = (Int16)(DU[0] - DC);
DC = DU[0];
if (Diff == 0)
WriteBits(HTDC[0],bw);
else
{
WriteBits(HTDC[Tables.Category[32767 + Diff]], bw);
WriteBits(Tables.BitCode[32767 + Diff], bw);
}
// Encode ACs
for (end0pos = 63; (end0pos > 0) && (DU[end0pos] == 0); end0pos--) ;
//end0pos = first element in reverse order != 0
i = 1;
while (i <= end0pos)
{
startpos = i;
for (; (DU[i] == 0) && (i <= end0pos); i++) ;
nrzeroes = (byte) (i - startpos);
if (nrzeroes >= 16)
{
for (nrmarker = 1; nrmarker <= nrzeroes / 16; nrmarker++)
WriteBits(M16zeroes,bw);
nrzeroes = (byte) (nrzeroes % 16);
}
WriteBits(HTAC[nrzeroes * 16 + Tables.Category[32767 + DU[i]]], bw);
WriteBits(Tables.BitCode[32767 + DU[i]], bw);
i++;
}
if (end0pos != 63)
WriteBits(EOB,bw);
}
void WriteBits(Tables.BitString bs, BinaryWriter bw)
{
UInt16 value;
SByte posval;
value = bs.value;
posval = (SByte)(bs.length - 1);
while (posval >= 0)
{
if ((value & mask[posval]) != 0)
{
bytenew = (Byte)(bytenew | mask[bytepos]);
}
posval--;
bytepos--;
if (bytepos < 0)
{
// Write to stream
if (bytenew == 0xFF)
{
// Handle special case
bw.Write((byte)(0xFF));
bw.Write((byte)(0x00));
}
else bw.Write((byte)(bytenew));
// Reinitialize
bytepos = 7;
bytenew = 0;
}
}
}
static void Compute_Huffman_Table(Byte[] nrCodes, Byte[] std_table, ref Tables.BitString[] Huffman_Table)
{
Byte k, j;
Byte pos_in_table;
UInt16 code_value;
code_value = 0;
pos_in_table = 0;
for (k = 1; k <= 16; k++)
{
for (j = 1; j <= nrCodes[k]; j++)
{
Huffman_Table[std_table[pos_in_table]].value = code_value;
Huffman_Table[std_table[pos_in_table]].length = k;
pos_in_table++;
code_value++;
}
code_value <<= 1;
}
}