static void GetHistogram(ref byte[] pBufIn, int lenIn, out HistogramNode[] pHN, out int lenOut)
{
int i;
HistogramNode[] pHFull = new HistogramNode[256];
for (i = 0; i < 256; i++)
{
pHFull[i] = new HistogramNode(Convert.ToByte(i));
}
for (i = 0; i < lenIn; i++)
{
pHFull[pBufIn[i]].Inc();
}
lenOut = pHFull.Count(x => x.Frequency > 0);
pHN = new HistogramNode[lenOut];
for (i = 0; i < lenOut; i++)
{
pHN[i] = new HistogramNode();
}
int index = -1;
for (i = 0; i < 256; i++)
{
if (pHFull[i].Frequency > 0)
{
index++;
pHN[index].Value = pHFull[i].Value;
pHN[index].Frequency = pHFull[i].Frequency;
}
}
}
static void DecodeArray(ref byte[] pBufIn, out byte[] pBufOut)
{
int lenIn = pBufIn.Length;
int lenOut = 0;
int offset = 1;
// 0 === check for compressed or uncompressed ===
if (pBufIn[0] == 0)
{
lenOut = BitConverter.ToInt32(pBufIn, offset); offset += sizeof(int);
pBufOut = new byte[lenOut];
Array.Copy(pBufIn, offset, pBufOut, 0, lenOut);
return;
}
// ==============================================
// 1 === Get Huffman table ===
int i;
int nHaffmanTableSize = BitConverter.ToInt32(pBufIn, offset);
offset += sizeof(int);
if (nHaffmanTableSize == 1)
{
int uncompressed = BitConverter.ToInt32(pBufIn, offset);
offset += sizeof(int);
byte Value = pBufIn[offset];
lenOut = uncompressed;
pBufOut = new byte[lenOut];
for (i = 0; i < lenOut; i++)
{
pBufOut[i] = Value;
}
return;
}
// === extract histogram ===
HistogramNode[] pHN = new HistogramNode[nHaffmanTableSize];
for (i = 0; i < nHaffmanTableSize; i++)
{
pHN[i] = new HistogramNode();
offset = pHN[i].FromArray(ref pBufIn, offset);
}
// =========================
// 2 === create zero level of tree ===
List <CHNode> arCHZeroLevel = new List <CHNode>();
int lHOut = nHaffmanTableSize;
for (i = 0; i < lHOut; i++)
{
arCHZeroLevel.Add(new CHNode(pHN[i].Value, pHN[i].Frequency));
}
// ===================================
// 3 === create tree ===
List <CHNode> arCHTree = new List <CHNode>(arCHZeroLevel);
int lCur = lHOut;
int nTreeSize;
CHNode pRoot = null;
while (lCur > 1)
{
int index1 = 0;
int index2 = 0;
CHNode emptyNode = null;
CHNode pHaffman = null;
int min = 0xFFFFFFF;
nTreeSize = arCHTree.Count;
for (i = 0; i < nTreeSize; i++)
{
pHaffman = arCHTree[i];
if (pHaffman.Mark)
{
continue;
}
if (pHaffman.Weight < min)
{
index1 = i;
min = pHaffman.Weight;
}
}
min = 0xFFFFFFF;
for (i = 0; i < nTreeSize; i++)
{
pHaffman = arCHTree[i];
if (pHaffman.Mark)
{
continue;
}
if (i == index1)
{
continue;
}
if (pHaffman.Weight < min)
{
index2 = i;
min = pHaffman.Weight;
}
}
CHNode p1 = arCHTree[index1];
CHNode p2 = arCHTree[index2];
CHNode pNewNode = new CHNode();
pNewNode.Weight = p1.Weight + p2.Weight;
pNewNode.SetLeft(ref p1);
pNewNode.SetRight(ref p2);
pNewNode.SetRoot(ref emptyNode);
pRoot = pNewNode;
arCHTree.Add(pNewNode);
p1.SetRoot(ref pNewNode);
p1.SetLeftType();
p1.Mark = true;
p2.SetRoot(ref pNewNode);
p2.SetRightType();
p2.Mark = true;
lCur--;
}
// === end: tree from encode ====
// 2 == get output size ===
lenOut = BitConverter.ToInt32(pBufIn, offset); offset += sizeof(int);
pBufOut = new byte[lenOut];
Array.Clear(pBufOut, 0, lenOut);
// ========================
// 3 === decoding ===
int offsetOut = 0;
int nBits = 8;
byte Digit;
CHNode pHaffman1;
while (offsetOut < lenOut)
{
pHaffman1 = pRoot;
while (true)
{
Digit = Convert.ToByte(pBufIn[offset] & (1 << (nBits - 1)));
Digit = Convert.ToByte(Digit >> (nBits - 1));
nBits--;
// === fast search huffman table index ===
pHaffman1 = (Digit == 0) ? pHaffman1.GetLeft() : pHaffman1.GetRight();
// =======================================
if (nBits == 0)
{
offset++;
nBits = 8;
}
if (pHaffman1.GetRight() == null)
{
break;
}
}
if (pHaffman1.GetRight() == null)
{
pBufOut[offsetOut++] = pHaffman1.Value;
}
else
{
break;
}
}
}