private void DecodeSymbol2(PpmContext context)
{
See2Context see2Context = MakeEscapeFrequency(context);
uint currentSymbol;
uint count;
uint highCount = 0;
uint index = (uint)(context.NumberStatistics - _numberMasked);
uint stateIndex = 0;
PpmState state = context.Statistics - 1;
do
{
do
{
currentSymbol = state[1].Symbol;
state++;
}while (_characterMask[currentSymbol] == _escapeCount);
highCount += state.Frequency;
_decodeStates[stateIndex++] = state;
// note that decodeStates is a static array that is re-used on each call to this method (for performance reasons)
}while (--index != 0);
_coder._scale += highCount;
count = _coder.RangeGetCurrentCount();
stateIndex = 0;
state = _decodeStates[stateIndex];
if (count < highCount)
{
highCount = 0;
while ((highCount += state.Frequency) <= count)
{
state = _decodeStates[++stateIndex];
}
_coder._highCount = highCount;
_coder._lowCount = _coder._highCount - state.Frequency;
see2Context.Update();
Update2(state, context);
}
else
{
_coder._lowCount = highCount;
_coder._highCount = _coder._scale;
index = (uint)(context.NumberStatistics - _numberMasked);
_numberMasked = context.NumberStatistics;
do
{
_characterMask[_decodeStates[stateIndex].Symbol] = _escapeCount;
stateIndex++;
}while (--index != 0);
see2Context._summary += (ushort)_coder._scale;
}
}
private void EncodeSymbol2(int symbol, PpmContext context)
{
See2Context see2Context = MakeEscapeFrequency(context);
uint currentSymbol;
uint lowCount = 0;
uint index = (uint)(context.NumberStatistics - _numberMasked);
PpmState state = context.Statistics - 1;
do
{
do
{
currentSymbol = state[1].Symbol;
state++;
}while (_characterMask[currentSymbol] == _escapeCount);
_characterMask[currentSymbol] = _escapeCount;
if (currentSymbol == symbol)
{
goto SymbolFound;
}
lowCount += state.Frequency;
}while (--index != 0);
_coder._lowCount = lowCount;
_coder._scale += _coder._lowCount;
_coder._highCount = _coder._scale;
see2Context._summary += (ushort)_coder._scale;
_numberMasked = context.NumberStatistics;
return;
SymbolFound:
_coder._lowCount = lowCount;
lowCount += state.Frequency;
_coder._highCount = lowCount;
for (PpmState p1 = state; --index != 0;)
{
do
{
currentSymbol = p1[1].Symbol;
p1++;
}while (_characterMask[currentSymbol] == _escapeCount);
lowCount += p1.Frequency;
}
_coder._scale += lowCount;
see2Context.Update();
Update2(state, context);
}
