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+// Copyright 2008 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Regular expression generator: generates all possible
+// regular expressions within given parameters (see below for details).
+
+#ifndef RE2_TESTING_REGEXP_GENERATOR_H__
+#define RE2_TESTING_REGEXP_GENERATOR_H__
+
+#include <string>
+#include <vector>
+#include "util/random.h"
+#include "util/util.h"
+#include "re2/stringpiece.h"
+
+namespace re2 {
+
+// Regular expression generator.
+//
+// Given a set of atom expressions like "a", "b", or "."
+// and operators like "%s*", generates all possible regular expressions
+// using at most maxbases base expressions and maxops operators.
+// For each such expression re, calls HandleRegexp(re).
+//
+// Callers are expected to subclass RegexpGenerator and provide HandleRegexp.
+//
+class RegexpGenerator {
+ public:
+  RegexpGenerator(int maxatoms, int maxops, const vector<string>& atoms,
+                  const vector<string>& ops);
+  virtual ~RegexpGenerator() {}
+
+  // Generates all the regular expressions, calling HandleRegexp(re) for each.
+  void Generate();
+
+  // Generates n random regular expressions, calling HandleRegexp(re) for each.
+  void GenerateRandom(int32 seed, int n);
+
+  // Handles a regular expression.  Must be provided by subclass.
+  virtual void HandleRegexp(const string& regexp) = 0;
+
+  // The egrep regexp operators: * + ? | and concatenation.
+  static const vector<string>& EgrepOps();
+
+ private:
+  void RunPostfix(const vector<string>& post);
+  void GeneratePostfix(vector<string>* post, int nstk, int ops, int lits);
+  bool GenerateRandomPostfix(vector<string>* post, int nstk, int ops, int lits);
+
+  int maxatoms_;           // Maximum number of atoms allowed in expr.
+  int maxops_;             // Maximum number of ops allowed in expr.
+  vector<string> atoms_;   // Possible atoms.
+  vector<string> ops_;     // Possible ops.
+  ACMRandom* acm_;         // Random generator.
+  DISALLOW_EVIL_CONSTRUCTORS(RegexpGenerator);
+};
+
+// Helpers for preparing arguments to RegexpGenerator constructor.
+
+// Returns one string for each character in s.
+vector<string> Explode(const StringPiece& s);
+
+// Splits string everywhere sep is found, returning
+// vector of pieces.
+vector<string> Split(const StringPiece& sep, const StringPiece& s);
+
+}  // namespace re2
+
+#endif  // RE2_TESTING_REGEXP_GENERATOR_H__