public void Update(IFrequencyTable freqs, int symbol)
{
var range = _high - _low + 1;
long total = freqs.GetTotal();
long symLow = freqs.GetLow(symbol);
long symHigh = freqs.GetHigh(symbol);
var newLow = _low + symLow * range / total;
var newHigh = _low + symHigh * range / total - 1;
_low = newLow;
_high = newHigh;
while (((_low ^ _high) & _halfRange) == 0)
{
Shift();
_low = ((_low << 1) & _stateMask);
_high = ((_high << 1) & _stateMask) | 1;
}
while ((_low & ~_high & _quarterRange) != 0)
{
Underflow();
_low = (_low << 1) ^ _halfRange;
_high = ((_high ^ _halfRange) << 1) | _halfRange | 1;
}
}
public int Read(IFrequencyTable freqs)
{
long total = freqs.GetTotal();
var range = _high - _low + 1;
var offset = _code - _low;
var value = ((offset + 1) * total - 1) / range;
var start = 0;
var end = freqs.GetSymbolLimit();
while (end - start > 1)
{
var middle = (start + end) >> 1;
if (freqs.GetLow(middle) > value)
{
end = middle;
}
else
{
start = middle;
}
}
var symbol = start;
Update(freqs, symbol);
return(symbol);
}
public PpmModel(int order, int escapeSymbol)
{
this.ModelOrder = order;
this._escapeSymbol = escapeSymbol;
if (order >= 0)
{
RootContext = new Context(order >= 1);
RootContext.Frequencies.Increment(escapeSymbol);
}
else
{
RootContext = null;
}
orderMinus1Freqs = new FlatFrequencyTable();
}
public Context(bool hasSubctx)
{
Frequencies = new SimpleFrequencyTable(new int[257]);
Subcontexts = hasSubctx ? new Context[257] : null;
}