public override IEnumerable <string> SampleMatches(int k, int randomseed) { // Zero is treated as no seed, instead using a system provided one Random random = randomseed != 0 ? new Random(randomseed) : new Random(); ISolver <TSet> solver = _builder._solver; CharSetSolver charSetSolver = _builder._charSetSolver; // Create helper BDDs for handling anchors and preferentially generating ASCII inputs BDD asciiWordCharacters = charSetSolver.Or(new BDD[] { charSetSolver.CreateBDDFromRange('A', 'Z'), charSetSolver.CreateBDDFromRange('a', 'z'), charSetSolver.CreateBDDFromChar('_'), charSetSolver.CreateBDDFromRange('0', '9') }); // Visible ASCII range for input character generation BDD ascii = charSetSolver.CreateBDDFromRange('\x20', '\x7E'); BDD asciiNonWordCharacters = charSetSolver.And(ascii, charSetSolver.Not(asciiWordCharacters)); // Set up two sets of minterms, one with the additional special minterm for the last end-of-line Debug.Assert(_builder._minterms is not null); int[] mintermIdsWithoutZ = new int[_builder._minterms.Length]; int[] mintermIdsWithZ = new int[_builder._minterms.Length + 1]; for (int i = 0; i < _builder._minterms.Length; ++i) { mintermIdsWithoutZ[i] = i; mintermIdsWithZ[i] = i; } mintermIdsWithZ[_builder._minterms.Length] = _builder._minterms.Length; for (int i = 0; i < k; i++) { // Holds the generated input so far StringBuilder inputSoFar = new(); StringBuilder?latestCandidate = null; // Current set of states reached initially contains just the root NfaMatchingState states = new(_builder); // Here one could also consider previous characters for example for \b, \B, and ^ anchors // and initialize inputSoFar accordingly states.InitializeFrom(_initialStates[GetCharKind(ReadOnlySpan <char> .Empty, -1)]); CurrentState statesWrapper = new(states); // Used for end suffixes List <string> possibleEndings = new(); while (true) { Debug.Assert(states.NfaStateSet.Count > 0); // Gather the possible endings for satisfying nullability possibleEndings.Clear(); if (NfaStateHandler.CanBeNullable(ref statesWrapper)) { // Unconditionally final state or end of the input due to \Z anchor for example if (NfaStateHandler.IsNullable(ref statesWrapper) || NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.BeginningEnd)) { possibleEndings.Add(""); } // End of line due to end-of-line anchor if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.Newline)) { possibleEndings.Add("\n"); } // Related to wordborder due to \b or \B if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.WordLetter)) { possibleEndings.Add(ChooseChar(random, asciiWordCharacters, ascii, charSetSolver).ToString()); } // Related to wordborder due to \b or \B if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.General)) { possibleEndings.Add(ChooseChar(random, asciiNonWordCharacters, ascii, charSetSolver).ToString()); } } // If we have a possible ending, then store a candidate input if (possibleEndings.Count > 0) { latestCandidate ??= new(); latestCandidate.Clear(); latestCandidate.Append(inputSoFar); //Choose some suffix that allows some anchor (if any) to be nullable latestCandidate.Append(Choose(random, possibleEndings)); // Choose to stop here based on a coin-toss if (FlipBiasedCoin(random, SampleMatchesStoppingProbability)) { yield return(latestCandidate.ToString()); break; } } // Shuffle the minterms, including the last end-of-line marker if appropriate int[] mintermIds = NfaStateHandler.StartsWithLineAnchor(_builder, ref statesWrapper) ? Shuffle(random, mintermIdsWithZ) : Shuffle(random, mintermIdsWithoutZ); foreach (int mintermId in mintermIds) { bool success = NfaStateHandler.TakeTransition(_builder, ref statesWrapper, mintermId); Debug.Assert(success); if (states.NfaStateSet.Count > 0) { TSet minterm = _builder.GetMinterm(mintermId); // Append a random member of the minterm inputSoFar.Append(ChooseChar(random, ToBDD(minterm, solver, charSetSolver), ascii, charSetSolver)); break; } else { // The transition was a dead end, undo and continue to try another minterm NfaStateHandler.UndoTransition(ref statesWrapper); } } // In the case that there are no next states or input has become too large: stop here if (states.NfaStateSet.Count == 0 || inputSoFar.Length > SampleMatchesMaxInputLength) { // Ending up here without an ending is unlikely but possible for example for infeasible patterns // such as @"no\bway" or due to poor choice of c -- no anchor is enabled -- so this is a deadend. if (latestCandidate != null) { yield return(latestCandidate.ToString()); } break; } } }