// allow zero-length tokens
captureSimState(prevAccept, input, ds0);
}
int t = input.LA(1);
@NotNull
DFAState s = ds0; // s is current/from DFA state
while ( true ) { // while more work
if ( debug ) {
System.out.format(Locale.getDefault(), "execATN loop starting closure: %s\n", s.configs);
}
// As we move src->trg, src->trg, we keep track of the previous trg to
// avoid looking up the DFA state again, which is expensive.
// If the previous target was already part of the DFA, we might
// be able to avoid doing a reach operation upon t. If s!=null,
// it means that semantic predicates didn't prevent us from
// creating a DFA state. Once we know s!=null, we check to see if
// the DFA state has an edge already for t. If so, we can just reuse
// it's configuration set; there's no point in re-computing it.
// This is kind of like doing DFA simulation within the ATN
// simulation because DFA simulation is really just a way to avoid
// computing reach/closure sets. Technically, once we know that
// we have a previously added DFA state, we could jump over to
// the DFA simulator. But, that would mean popping back and forth
// a lot and making things more complicated algorithmically.
// This optimization makes a lot of sense for loops within DFA.
// A character will take us back to an existing DFA state
// that already has lots of edges out of it. e.g., .* in comments.
DFAState target = getExistingTargetState(s, t);
if (target == null) {
target = computeTargetState(input, s, t);
}
if (target == ERROR) {