/// <summary>
/// Find the longest match starting at a given position.
///
/// If there is a non-empty match for the DFA in the source string starting at startPos,
/// then the LastMatchStart position is set to startPos, the LastMatchEnd position is set
/// to the end of the longest such match, and the TResult from that match is returned.
/// </summary>
/// <param name="state">The start state of the DFA for the patterns you want to match</param>
/// <param name="startPos">the position in the source string to test for a match</param>
/// <param name="val">The TResult that the pattern matches</param>
/// <returns>True if the source string matches a pattern in the DFA at startPos. Otherwise false.</returns>
public bool MatchAt(DfaState <TResult> state, int startPos, out TResult val)
{
val = default;
var ret = false;
var newNmmSize = 0;
var writeNmmNext = startPos + 4;
for (var pos = startPos; pos < limit;)
{
state = state.GetNextState(src[pos]);
pos++;
if (state == null)
{
break;
}
if (state.IsAccepting)
{
ret = true;
val = state.Match;
LastMatchEnd = pos;
newNmmSize = 0;
continue;
}
//Check and update the non-matching memo, to accelerate processing long sequences
//of non-accepting states at multiple positions
//Many DFAs simply don't have long sequences of non-accepting states, so we only
//want to incur this overhead when we're actually in a non-accepting state
bool exitPosLoop = false;
while (!exitPosLoop && nmmStart < NmmSize && nmmPositions[nmmStart] <= pos)
{
if (nmmPositions[nmmStart] == pos && nmmStates[nmmStart] == state)
{
//hit the memo -- we won't find a match.
exitPosLoop = true;
}
//we passed this memo entry without using it -- remove it.
++nmmStart;
}
if (exitPosLoop)
{
break;
}
if (pos >= writeNmmNext && newNmmSize < NmmSize)
{
nmmPositions[newNmmSize] = pos;
nmmStates[newNmmSize] = state;
++newNmmSize;
writeNmmNext = pos + (2 << newNmmSize);
if (nmmStart < newNmmSize)
{
nmmStart = newNmmSize;
}
}
}
//successful or not, we're done. Merge in our new entries for the non-matching memo
while (nmmStart < NmmSize && nmmPositions[nmmStart] < writeNmmNext)
{
++nmmStart;
}
while (newNmmSize > 0)
{
--newNmmSize;
--nmmStart;
nmmPositions[nmmStart] = nmmPositions[newNmmSize];
nmmStates[nmmStart] = nmmStates[newNmmSize];
}
if (ret)
{
LastMatchStart = startPos;
}
return(ret);
}