public void Compress(Stream inStream, BitOutputStream outStream)
{
var enc = new ArithmeticEncoder(outStream);
var model = new PpmModel(ModelOrder, EscapeSymbol);
var history = new int[0];
while (true)
{
var symbol = inStream.ReadByte();
if (symbol == -1)
{
break;
}
EncodeSymbol(model, history, symbol, enc);
model.IncrementContexts(history, symbol);
if (model.ModelOrder >= 1)
{
if (history.Length < model.ModelOrder)
{
Array.Resize(ref history, history.Length + 1);
}
Array.Copy(history, 0, history, 1, history.Length - 1);
history[0] = symbol;
}
}
EncodeSymbol(model, history, EscapeSymbol, enc);
enc.Finish();
}
private static void EncodeSymbol(PpmModel model, int[] history, int symbol, ArithmeticEncoder enc)
{
var order = history.Length;
while (order >= 0)
{
var isBreak = false;
var ctx = model.RootContext;
for (var i = 0; i < order; i++)
{
ctx = ctx.Subcontexts[history[i]];
if (ctx == null)
{
order--;
isBreak = true;
break;
}
}
if (isBreak)
{
continue;
}
if (symbol != EscapeSymbol && ctx.Frequencies.Get(symbol) > 0)
{
enc.Write(ctx.Frequencies, symbol);
return;
}
enc.Write(ctx.Frequencies, EscapeSymbol);
order--;
}
enc.Write(model.orderMinus1Freqs, symbol);
}
