getPredsForAmbigAlts method

List<SemanticContext?>? getPredsForAmbigAlts(BitSet ambigAlts, ATNConfigSet configs, int nalts)

Implementation

List<SemanticContext?>? getPredsForAmbigAlts(
  BitSet ambigAlts,
  ATNConfigSet configs,
  int nalts,
) {
  // REACH=[1|1|[]|0:0, 1|2|[]|0:1]
  /* altToPred starts as an array of all null contexts. The entry at index i
		 * corresponds to alternative i. altToPred[i] may have one of three values:
		 *   1. null: no ATNConfig c is found such that c.alt==i
		 *   2. SemanticContext.NONE: At least one ATNConfig c exists such that
		 *      c.alt==i and c.semanticContext==SemanticContext.NONE. In other words,
		 *      alt i has at least one unpredicated config.
		 *   3. Non-NONE Semantic Context: There exists at least one, and for all
		 *      ATNConfig c such that c.alt==i, c.semanticContext!=SemanticContext.NONE.
		 *
		 * From this, it is clear that NONE||anything==NONE.
		 */
  final altToPred = List<SemanticContext?>.filled(nalts + 1, null);

  for (var c in configs) {
    if (ambigAlts[c.alt]) {
      altToPred[c.alt] =
          SemanticContext.or(altToPred[c.alt], c.semanticContext);
    }
  }

  var nPredAlts = 0;
  for (var i = 1; i <= nalts; i++) {
    if (altToPred[i] == null) {
      altToPred[i] = EmptySemanticContext.Instance;
    } else if (altToPred[i] != EmptySemanticContext.Instance) {
      nPredAlts++;
    }
  }

//		// Optimize away p||p and p&&p TODO: optimize() was a no-op
//		for (int i = 0; i < altToPred.length; i++) {
//			altToPred[i] = altToPred[i].optimize();
//		}

  if (debug) log('getPredsForAmbigAlts result $altToPred');
  // nonambig alts are null in altToPred
  if (nPredAlts == 0) return null;
  return altToPred;
}