private static void GenerateCodes(HuffmanTreeNode node, uint code, uint depth)
{
if (node.IsLeaf())
{
node.NumBits = depth;
node.Code = code;
}
else
{
var leftCode = code & ~(1U << (int)depth);
GenerateCodes(node.Left, leftCode, depth + 1);
var rightCode = code | (1U << (int)depth);
GenerateCodes(node.Right, rightCode, depth + 1);
}
}
public static void Build()
{
if (TablesBuilt)
{
return;
}
TablesBuilt = true;
var nodes = new HuffmanTreeNode[256];
var currCount = 256;
for (var i = 0; i < 256; ++i)
{
nodes[i] = new HuffmanTreeNode
{
Symbol = (byte)i,
Frequency = CharFreqs[i] + 1,
NumBits = 0,
Code = 0,
Left = null,
Right = null
};
Leaves.Add((byte)i, nodes[i]);
}
while (currCount != 1)
{
uint min1 = 0xFFFFFFFEU, min2 = 0xFFFFFFFFU;
int index1 = -1, index2 = -1;
for (var i = 0; i < currCount; ++i)
{
if (nodes[i].Frequency < min1)
{
min2 = min1;
index2 = index1;
min1 = nodes[i].Frequency;
index1 = i;
}
else if (nodes[i].Frequency < min2)
{
min2 = nodes[i].Frequency;
index2 = i;
}
}
if (index1 != -1 && index2 != -1 && index1 != index2)
{
var node1 = nodes[index1];
var node2 = nodes[index2];
var parent = new HuffmanTreeNode
{
Symbol = (byte)'*',
Frequency = node1.Frequency + node2.Frequency,
Left = node1,
Right = node2
};
nodes[index1 > index2 ? index2 : index1] = parent;
if (index2 != (currCount - 1))
{
nodes[index1 > index2 ? index1 : index2] = nodes[currCount - 1];
}
--currCount;
}
Root = nodes[0];
}
GenerateCodes(Root, 0, 0);
}
public static bool IsLeaf(HuffmanTreeNode node)
{
return(node.IsLeaf());
}
