////////////////////////////////////////////////////////////////////
// Build code array from bit length frequency distribution
////////////////////////////////////////////////////////////////////
public void BuildCodes()
{
// build bit length frequency array
Array.Clear(BitLengthFreq, 0, BitLengthFreq.Length);
for (Int32 Code = 0; Code < MaxUsedCodes; Code++)
{
if (CodeLength[Code] != 0)
{
BitLengthFreq[CodeLength[Code] - 1]++;
}
}
// build array of initial code for each block of codes
Int32 InitCode = 0;
for (Int32 BitNo = 0; BitNo < MaxBitLength; BitNo++)
{
// save the initial code of the block
FirstCode[BitNo] = InitCode;
// advance the code by the frequancy times 2 to the power of 15 less bit length
InitCode += BitLengthFreq[BitNo] << (15 - BitNo);
}
// it must add up to 2 ** 16
if (InitCode != 65536)
{
throw new ApplicationException("Inconsistent bl_counts!");
}
// now fill up the entire code array
Array.Clear(Codes, 0, Codes.Length);
for (Int32 Index = 0; Index < MaxUsedCodes; Index++)
{
Int32 Bits = CodeLength[Index];
if (Bits > 0)
{
Codes[Index] = BitReverse.Reverse16Bits(FirstCode[Bits - 1]);
FirstCode[Bits - 1] += 1 << (16 - Bits);
}
}
// exit
return;
}
/// <summary>
/// Build code array from bit length frequency distribution
/// </summary>
/// <exception cref="System.Exception">Inconsistent bl_counts!</exception>
public void BuildCodes()
{
// build bit length frequency array
Array.Clear(_bitLengthFreq, 0, _bitLengthFreq.Length);
for (int code = 0; code < MaxUsedCodes; code++)
{
if (_codeLength[code] != 0)
{
_bitLengthFreq[_codeLength[code] - 1]++;
}
}
// build array of initial code for each block of codes
int initCode = 0;
for (int bitNo = 0; bitNo < _maxBitLength; bitNo++)
{
// save the initial code of the block
_firstCode[bitNo] = initCode;
// advance the code by the frequancy times 2 to the power of 15 less bit length
initCode += _bitLengthFreq[bitNo] << (15 - bitNo);
}
// it must add up to 2 ** 16
if (initCode != 65536)
{
throw new Exception("Inconsistent bl_counts!");
}
// now fill up the entire code array
Array.Clear(_codes, 0, _codes.Length);
for (int index = 0; index < MaxUsedCodes; index++)
{
int bits = _codeLength[index];
if (bits > 0)
{
_codes[index] = BitReverse.Reverse16Bits(_firstCode[bits - 1]);
_firstCode[bits - 1] += 1 << (16 - bits);
}
}
}
////////////////////////////////////////////////////////////////////
// Constructs a Huffman tree from the array of code lengths.
////////////////////////////////////////////////////////////////////
public void BuildTree
(
Byte[] CodeLengths,
Int32 Offset,
Int32 Length
)
{
// Build frequency array for bit length 1 to 15
// Note: BitLengthCount[0] will never be used.
// All elements of CodeLength are greater than zero.
// In other words no code has zero length
Array.Clear(BitLengthCount, 0, BitLengthCount.Length);
for (Int32 Index = 0; Index < Length; Index++)
{
BitLengthCount[CodeLengths[Offset + Index]]++;
}
// build array of inital codes for each group of equal code length
Int32 InitCode = 0;
for (Int32 Bits = 1; Bits <= MAX_BITLEN; Bits++)
{
InitialCode[Bits] = InitCode;
InitCode += BitLengthCount[Bits] << (16 - Bits);
}
if (InitCode != 65536)
{
throw new ApplicationException("Code lengths don't add up properly.");
}
// longest code bit count
Int32 MaxBits;
for (MaxBits = MAX_BITLEN; BitLengthCount[MaxBits] == 0; MaxBits--)
{
;
}
// number of hash bits at the root of the decode tree
// the longest code but no more than 9 bits
Int32 ActiveHashBits = Math.Min(9, MaxBits);
// the decoding process is using this bit mask
ActiveBitMask = 1 << ActiveHashBits;
// hash table at the begining of the tree
Array.Clear(ActiveTree, 0, ActiveTree.Length);
// pointer to the area above the hash table for codes longer than hash bits
Int32 EndPtr = ActiveBitMask;
// fill the tree
for (Int32 Index = 0; Index < Length; Index++)
{
// code length in bits
Int32 Bits = CodeLengths[Offset + Index];
// code not in use
if (Bits == 0)
{
continue;
}
// reverse the code from the most significant part to the least significant part of the integer
Int32 Code = BitReverse.Reverse16Bits(InitialCode[Bits]);
// the number of bits is less than the hash bits
// we need to add artificial entries for the missing bits
if (Bits < ActiveHashBits)
{
Int32 NextInc = (1 << Bits);
for (Int32 Next = Code; Next < ActiveBitMask; Next += NextInc)
{
ActiveTree[Next] = ~(Index << 4 | Bits);
}
}
// the number of bits is equal to the hash bits
else if (Bits == ActiveHashBits)
{
ActiveTree[Code] = ~(Index << 4 | Bits);
}
// the number of bits is greater than the hash bits
else
{
// hash pointer to the start of the tree table
Int32 HashPtr = Code & (ActiveBitMask - 1);
// get the value at this location
Int32 Next = ActiveTree[HashPtr];
// the location is not initialized
if (Next == 0)
{
// get a free node at the area above the hash area and link it to the tree
ActiveTree[HashPtr] = EndPtr;
Next = EndPtr;
EndPtr += 2;
}
// navigate through the tree above the hash area
// add empty nodes as required
Int32 BitMaskEnd = 1 << (Bits - 1);
for (Int32 BitMask = ActiveBitMask; BitMask != BitMaskEnd; BitMask <<= 1)
{
// current bit is one, adjust the next pointer
if ((Code & BitMask) != 0)
{
Next++;
}
// get the value at this location
Int32 Next1 = ActiveTree[Next];
// the location was initialized before, continue to follow the path
if (Next1 > 0)
{
Next = Next1;
continue;
}
// add free node from the area above the hash table and link it to the tree
ActiveTree[Next] = EndPtr;
Next = EndPtr;
EndPtr += 2;
}
// we are now at a leaf point, add the symbol and the number of bits
if ((Code & BitMaskEnd) != 0)
{
Next++;
}
ActiveTree[Next] = ~(Index << 4 | Bits);
}
// update initial code for the next code with the same number of bits
InitialCode[Bits] += 1 << (16 - Bits);
}
// exit
return;
}
/// <summary>
/// Constructs a Huffman tree from the array of code lengths.
/// </summary>
/// <param name="codeLengths">The code lengths.</param>
/// <param name="offset">The offset.</param>
/// <param name="length">The length.</param>
public void BuildTree(byte[] codeLengths, int offset, int length)
{
// Build frequency array for bit length 1 to 15
// Note: BitLengthCount[0] will never be used.
// All elements of CodeLength are greater than zero.
// In other words no code has zero length
Array.Clear(_bitLengthCount, 0, _bitLengthCount.Length);
for (int index = 0; index < length; index++)
{
_bitLengthCount[codeLengths[offset + index]]++;
}
// build array of inital codes for each group of equal code length
int initCode = 0;
for (int bits = 1; bits <= MaxBitlen; bits++)
{
_initialCode[bits] = initCode;
initCode += _bitLengthCount[bits] << (16 - bits);
}
// Warning
// If BitLengthCount array was constructed properly InitCode should be equal to 65536.
// During all my initial testing of decompressing ZIP archives coming from other programs
// that was the case. I finally run into one file that was compressed by old version
// of PKZIP version 2.50 4-15-1998 that the following commented statement threw exception.
// I would strongly recomment to anyone making modification to the compression/decompression
// software to activate this statement during the testing.
//
//if(InitCode != 65536) throw new Exception("Code lengths don't add up properly.");
//
// longest code bit count
int maxBits;
for (maxBits = MaxBitlen; _bitLengthCount[maxBits] == 0; maxBits--)
{
}
// number of hash bits at the root of the decode tree
// the longest code but no more than 9 bits
int activeHashBits = Math.Min(9, maxBits);
// the decoding process is using this bit mask
ActiveBitMask = 1 << activeHashBits;
// hash table at the begining of the tree
Array.Clear(ActiveTree, 0, ActiveTree.Length);
// pointer to the area above the hash table for codes longer than hash bits
int endPtr = ActiveBitMask;
// fill the tree
for (int index = 0; index < length; index++)
{
// code length in bits
int Bits = codeLengths[offset + index];
// code not in use
if (Bits == 0)
{
continue;
}
// reverse the code from the most significant part to the least significant part of the integer
int code = BitReverse.Reverse16Bits(_initialCode[Bits]);
// the number of bits is less than the hash bits
// we need to add artificial entries for the missing bits
if (Bits < activeHashBits)
{
int nextInc = (1 << Bits);
for (int next = code; next < ActiveBitMask; next += nextInc)
{
ActiveTree[next] = ~(index << 4 | Bits);
}
}
// the number of bits is equal to the hash bits
else if (Bits == activeHashBits)
{
ActiveTree[code] = ~(index << 4 | Bits);
}
// the number of bits is greater than the hash bits
else
{
// hash pointer to the start of the tree table
int hashPtr = code & (ActiveBitMask - 1);
// get the value at this location
int next = ActiveTree[hashPtr];
// the location is not initialized
if (next == 0)
{
// get a free node at the area above the hash area and link it to the tree
ActiveTree[hashPtr] = endPtr;
next = endPtr;
endPtr += 2;
}
// navigate through the tree above the hash area
// add empty nodes as required
int bitMaskEnd = 1 << (Bits - 1);
for (int bitMask = ActiveBitMask; bitMask != bitMaskEnd; bitMask <<= 1)
{
// current bit is one, adjust the next pointer
if ((code & bitMask) != 0)
{
next++;
}
// get the value at this location
int next1 = ActiveTree[next];
// the location was initialized before, continue to follow the path
if (next1 > 0)
{
next = next1;
continue;
}
// add free node from the area above the hash table and link it to the tree
ActiveTree[next] = endPtr;
next = endPtr;
endPtr += 2;
}
// we are now at a leaf point, add the symbol and the number of bits
if ((code & bitMaskEnd) != 0)
{
next++;
}
ActiveTree[next] = ~(index << 4 | Bits);
}
// update initial code for the next code with the same number of bits
_initialCode[Bits] += 1 << (16 - Bits);
}
}