/// <summary>
/// Write the tree to output file
/// </summary>
/// <param name="blTree">The bl tree.</param>
public void WriteTree(DeflateTree blTree)
{
for (int code = 0; code < MaxUsedCodes;)
{
// current code length
int codeLen = _codeLength[code];
// scan the code array for equal code lengths
int count = 1;
for (code++; code < MaxUsedCodes && codeLen == _codeLength[code]; code++)
{
count++;
}
// less than three equal code length
if (count < 3)
{
// write the first code length to output file
blTree.WriteSymbol(codeLen);
// write the second code length to output file
if (count > 1)
{
blTree.WriteSymbol(codeLen);
}
continue;
}
// Used code. Code length is other than zero.
if (codeLen != 0)
{
// write the code length to output file
blTree.WriteSymbol(codeLen);
// reduce the count by one
count--;
// for every full block of 6 repeats add one REP_3_6 code and two bits of 1 (11)
for (int index = count / 6; index > 0; index--)
{
blTree.WriteSymbol(RepeatSymbol_3_6);
_writeBits(6 - 3, 2);
}
// get the remainder
if ((count = count % 6) == 0)
{
continue;
}
// remainder is less than 3
if (count < 3)
{
// write the code length to output file
blTree.WriteSymbol(codeLen);
if (count > 1)
{
blTree.WriteSymbol(codeLen);
}
continue;
}
// remainder is beween 3 to 5
blTree.WriteSymbol(RepeatSymbol_3_6);
_writeBits(count - 3, 2);
continue;
}
// code length is zero and count is 3 or more
// for every full block of 138 repeats add one REP_11_138 code plus 7 bits of 1
for (int index = count / 138; index > 0; index--)
{
blTree.WriteSymbol(RepeatSymbol_11_138);
_writeBits(138 - 11, 7);
}
// get the remainder
if ((count = count % 138) == 0)
{
continue;
}
// remainder is less than 3
if (count < 3)
{
// write the code length to output file
blTree.WriteSymbol(codeLen);
if (count > 1)
{
blTree.WriteSymbol(codeLen);
}
continue;
}
// remainder is beween 3 to 10
if (count <= 10)
{
blTree.WriteSymbol(RepeatSymbol_3_10);
_writeBits(count - 3, 3);
continue;
}
// remainder is beween 11 to 137
blTree.WriteSymbol(RepeatSymbol_11_138);
_writeBits(count - 11, 7);
}
}
////////////////////////////////////////////////////////////////////
// calculate Bit Length frequency
/// 0 - 15: Represent code lengths of 0 - 15
// 16: Copy the previous code length 3 - 6 times.
// The next 2 bits indicate repeat length
// (0 = 3, ... , 3 = 6)
// Example: Codes 8, 16 (+2 bits 11), 16 (+2 bits 10) will expand to
// 12 code lengths of 8 (1 + 6 + 5)
// 17: Repeat a code length of 0 for 3 - 10 times. (3 bits of length)
// 18: Repeat a code length of 0 for 11 - 138 times. (7 bits of length)
////////////////////////////////////////////////////////////////////
public Int32 CalcBLFreq(DeflateTree blTree)
{
int extraBits = 0;
for (int code = 0; code < MaxUsedCodes;)
{
// current code length
int codeLen = _codeLength[code];
// scan the code array for equal code lengths
int count = 1;
for (code++; code < MaxUsedCodes && codeLen == _codeLength[code]; code++)
{
count++;
}
// less than three equal code length
if (count < 3)
{
blTree.CodeFreq[codeLen] += (short)count;
continue;
}
// code length is other than zero
if (codeLen != 0)
{
// add one to the frequency of the code itself
blTree.CodeFreq[codeLen]++;
// reduce the count by one
count--;
// for every full block of 6 repeats add one REP_3_6 code
blTree.CodeFreq[RepeatSymbol_3_6] += count / 6;
extraBits += 2 * (count / 6);
// get the remainder
if ((count = count % 6) == 0)
{
continue;
}
// remainder is less than 3
if (count < 3)
{
blTree.CodeFreq[codeLen] += count;
continue;
}
// remainder is beween 3 to 5
blTree.CodeFreq[RepeatSymbol_3_6]++;
extraBits += 2;
continue;
}
// code length is zero and count is 3 or more
// for every full block of 138 repeats add one REP_11_138 code
blTree.CodeFreq[RepeatSymbol_11_138] += count / 138;
extraBits += 7 * (count / 138);
// get the remainder
if ((count = count % 138) == 0)
{
continue;
}
// remainder is less than 3
if (count < 3)
{
blTree.CodeFreq[codeLen] += count;
continue;
}
// remainder is beween 3 to 10
if (count <= 10)
{
blTree.CodeFreq[RepeatSymbol_3_10]++;
extraBits += 3;
continue;
}
// remainder is beween 11 to 137
blTree.CodeFreq[RepeatSymbol_11_138]++;
extraBits += 7;
}
return(extraBits);
}