public void Decompress(BitInputStream inStream, Stream outStream)
{
var dec = new ArithmeticDecoder(inStream);
var model = new PpmModel(ModelOrder, 256);
var history = new int[0];
while (true)
{
var symbol = DecodeSymbol(dec, model, history);
if (symbol == 256)
{
break;
}
outStream.WriteByte((byte)symbol);
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;
}
}
}
private static int DecodeSymbol(ArithmeticDecoder dec, PpmModel model, int[] history)
{
var order = history.Length;
while (order >= 0)
{
var ctx = model.RootContext;
var isBreak = false;
for (var i = 0; i < order; i++)
{
ctx = ctx.Subcontexts[history[i]];
if (ctx == null)
{
order--;
isBreak = true;
break;
}
}
if (isBreak)
{
continue;
}
var symbol = dec.Read(ctx.Frequencies);
if (symbol < 256)
{
return(symbol);
}
order--;
}
return(dec.Read(model.orderMinus1Freqs));
}
