private double CalculateSecondOrderEntropy()
{
double entropy = 0;
foreach (var byteProb in this.SecondOrderProbabilities)
{
Comb2 prevBytes = new Comb2(byteProb.Key.Previous, byteProb.Key.PPrevious);
double pprevByteProb = this.ZeroOrderProbabilities[prevBytes.Previous];
double prevBytesProb = this.FirstOrderProbabilities[prevBytes];
entropy += pprevByteProb * prevBytesProb * byteProb.Value * Math.Log2(byteProb.Value);
}
entropy *= -1;
return(entropy);
}
private Dictionary <Comb2, double> CalculateFirstOrderProbabilities()
{
int bytesCount = this.Bytes.Count;
Dictionary <Comb2, int> bytesCounts = new Dictionary <Comb2, int>();
for (int i = 1; i < bytesCount; i++)
{
Comb2 comb = new Comb2(this.Bytes[i], this.Bytes[i - 1]);
if (!bytesCounts.ContainsKey(comb))
{
bytesCounts[comb] = 0;
}
bytesCounts[comb]++;
}
Dictionary <Comb2, double> probabilities = new Dictionary <Comb2, double>();
Dictionary <byte, int> prevByteCombinationsCount = new Dictionary <byte, int>();
foreach (var byteCount in bytesCounts)
{
byte prevByte = byteCount.Key.Previous;
int combinationsCount = 0;
if (!prevByteCombinationsCount.ContainsKey(prevByte))
{
combinationsCount = bytesCounts.Where(x => x.Key.Previous == prevByte).Sum(x => x.Value);
prevByteCombinationsCount[prevByte] = combinationsCount;
}
else
{
combinationsCount = prevByteCombinationsCount[prevByte];
}
probabilities[byteCount.Key] = (double)byteCount.Value / combinationsCount;
}
return(probabilities);
}
private Dictionary <Comb3, double> CalculateSecondOrderProbabilities()
{
int bytesCount = this.Bytes.Count;
Dictionary <Comb3, int> bytesCounts = new Dictionary <Comb3, int>();
for (int i = 2; i < bytesCount; i++)
{
Comb3 comb = new Comb3(this.Bytes[i], this.Bytes[i - 1], this.Bytes[i - 2]);
if (!bytesCounts.ContainsKey(comb))
{
bytesCounts[comb] = 0;
}
bytesCounts[comb]++;
}
Dictionary <Comb3, double> probabilities = new Dictionary <Comb3, double>();
Dictionary <Comb2, int> prevByteCombinationsCount = new Dictionary <Comb2, int>();
foreach (var byteCount in bytesCounts)
{
Comb2 prevBytes = new Comb2(byteCount.Key.Previous, byteCount.Key.PPrevious);
int combinationsCount = 0;
if (!prevByteCombinationsCount.ContainsKey(prevBytes))
{
combinationsCount = bytesCounts.Where(x => new Comb2(x.Key.Previous, x.Key.PPrevious).Equals(prevBytes)).Sum(x => x.Value);
prevByteCombinationsCount[prevBytes] = combinationsCount;
}
else
{
combinationsCount = prevByteCombinationsCount[prevBytes];
}
probabilities[byteCount.Key] = (double)byteCount.Value / combinationsCount;
}
return(probabilities);
}
