Antlr4.Runtime.Atn.ParserATNSimulator.GetPredsForAmbigAlts C# (CSharp) Method

        protected SemanticContext[] GetPredsForAmbigAlts(BitSet ambigAlts,
														 ATNConfigSet configSet,
													  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.
             */
            SemanticContext[] altToPred = new SemanticContext[nalts + 1];
            foreach (ATNConfig c in configSet.configs)
            {
                if (ambigAlts[c.alt])
                {
                    altToPred[c.alt] = SemanticContext.OrOp(altToPred[c.alt], c.semanticContext);
                }
            }

            int nPredAlts = 0;
            for (int i = 1; i <= nalts; i++)
            {
                if (altToPred[i] == null)
                {
                    altToPred[i] = SemanticContext.NONE;
                }
                else if (altToPred[i] != SemanticContext.NONE)
                {
                    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();
            //		}

            // nonambig alts are null in altToPred
            if (nPredAlts == 0) altToPred = null;
            if (debug) Console.WriteLine("getPredsForAmbigAlts result " + Arrays.ToString(altToPred));
            return altToPred;
        }