Replace RE2 import with a dependency

third_party/re2/re2/dfa.cc

-// 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.
-
-// A DFA (deterministic finite automaton)-based regular expression search.
-//
-// The DFA search has two main parts: the construction of the automaton,
-// which is represented by a graph of State structures, and the execution
-// of the automaton over a given input string.
-//
-// The basic idea is that the State graph is constructed so that the
-// execution can simply start with a state s, and then for each byte c in
-// the input string, execute "s = s->next[c]", checking at each point whether
-// the current s represents a matching state.
-//
-// The simple explanation just given does convey the essence of this code,
-// but it omits the details of how the State graph gets constructed as well
-// as some performance-driven optimizations to the execution of the automaton.
-// All these details are explained in the comments for the code following
-// the definition of class DFA.
-//
-// See http://swtch.com/~rsc/regexp/ for a very bare-bones equivalent.
-
-#include "util/atomicops.h"
-#include "util/flags.h"
-#include "util/sparse_set.h"
-#include "re2/prog.h"
-#include "re2/stringpiece.h"
-
-DEFINE_bool(re2_dfa_bail_when_slow, true,
-            "Whether the RE2 DFA should bail out early "
-            "if the NFA would be faster (for testing).");
-
-namespace re2 {
-
-#if !defined(__linux__)  /* only Linux seems to have memrchr */
-static void* memrchr(const void* s, int c, size_t n) {
-  const unsigned char* p = (const unsigned char*)s;
-  for (p += n; n > 0; n--)
-    if (*--p == c)
-      return (void*)p;
-
-  return NULL;
-}
-#endif
-
-// Changing this to true compiles in prints that trace execution of the DFA.
-// Generates a lot of output -- only useful for debugging.
-static const bool DebugDFA = false;
-
-// A DFA implementation of a regular expression program.
-// Since this is entirely a forward declaration mandated by C++,
-// some of the comments here are better understood after reading
-// the comments in the sections that follow the DFA definition.
-class DFA {
- public:
-  DFA(Prog* prog, Prog::MatchKind kind, int64 max_mem);
-  ~DFA();
-  bool ok() const { return !init_failed_; }
-  Prog::MatchKind kind() { return kind_; }
-
-  // Searches for the regular expression in text, which is considered
-  // as a subsection of context for the purposes of interpreting flags
-  // like ^ and $ and \A and \z.
-  // Returns whether a match was found.
-  // If a match is found, sets *ep to the end point of the best match in text.
-  // If "anchored", the match must begin at the start of text.
-  // If "want_earliest_match", the match that ends first is used, not
-  //   necessarily the best one.
-  // If "run_forward" is true, the DFA runs from text.begin() to text.end().
-  //   If it is false, the DFA runs from text.end() to text.begin(),
-  //   returning the leftmost end of the match instead of the rightmost one.
-  // If the DFA cannot complete the search (for example, if it is out of
-  //   memory), it sets *failed and returns false.
-  bool Search(const StringPiece& text, const StringPiece& context,
-              bool anchored, bool want_earliest_match, bool run_forward,
-              bool* failed, const char** ep, vector<int>* matches);
-
-  // Builds out all states for the entire DFA.  FOR TESTING ONLY
-  // Returns number of states.
-  int BuildAllStates();
-
-  // Computes min and max for matching strings.  Won't return strings
-  // bigger than maxlen.
-  bool PossibleMatchRange(string* min, string* max, int maxlen);
-
-  // These data structures are logically private, but C++ makes it too
-  // difficult to mark them as such.
-  class Workq;
-  class RWLocker;
-  class StateSaver;
-
-  // A single DFA state.  The DFA is represented as a graph of these
-  // States, linked by the next_ pointers.  If in state s and reading
-  // byte c, the next state should be s->next_[c].
-  struct State {
-    inline bool IsMatch() const { return (flag_ & kFlagMatch) != 0; }
-    void SaveMatch(vector<int>* v);
-
-    int* inst_;         // Instruction pointers in the state.
-    int ninst_;         // # of inst_ pointers.
-    uint flag_;         // Empty string bitfield flags in effect on the way
-                        // into this state, along with kFlagMatch if this
-                        // is a matching state.
-    State** next_;      // Outgoing arrows from State,
-                        // one per input byte class
-  };
-
-  enum {
-    kByteEndText = 256,         // imaginary byte at end of text
-
-    kFlagEmptyMask = 0xFFF,     // State.flag_: bits holding kEmptyXXX flags
-    kFlagMatch = 0x1000,        // State.flag_: this is a matching state
-    kFlagLastWord = 0x2000,     // State.flag_: last byte was a word char
-    kFlagNeedShift = 16,        // needed kEmpty bits are or'ed in shifted left
-  };
-
-#ifndef STL_MSVC
-  // STL function structures for use with unordered_set.
-  struct StateEqual {
-    bool operator()(const State* a, const State* b) const {
-      if (a == b)
-        return true;
-      if (a == NULL || b == NULL)
-        return false;
-      if (a->ninst_ != b->ninst_)
-        return false;
-      if (a->flag_ != b->flag_)
-        return false;
-      for (int i = 0; i < a->ninst_; i++)
-        if (a->inst_[i] != b->inst_[i])
-          return false;
-      return true;  // they're equal
-    }
-  };
-#endif  // STL_MSVC
-  struct StateHash {
-    size_t operator()(const State* a) const {
-      if (a == NULL)
-        return 0;
-      const char* s = reinterpret_cast<const char*>(a->inst_);
-      int len = a->ninst_ * sizeof a->inst_[0];
-      if (sizeof(size_t) == sizeof(uint32))
-        return Hash32StringWithSeed(s, len, a->flag_);
-      else
-        return static_cast<size_t>(Hash64StringWithSeed(s, len, a->flag_));
-    }
-#ifdef STL_MSVC
-    // Less than operator.
-    bool operator()(const State* a, const State* b) const {
-      if (a == b)
-        return false;
-      if (a == NULL || b == NULL)
-        return a == NULL;
-      if (a->ninst_ != b->ninst_)
-        return a->ninst_ < b->ninst_;
-      if (a->flag_ != b->flag_)
-        return a->flag_ < b->flag_;
-      for (int i = 0; i < a->ninst_; ++i)
-        if (a->inst_[i] != b->inst_[i])
-          return a->inst_[i] < b->inst_[i];
-      return false;  // they're equal
-    }
-    // The two public members are required by msvc. 4 and 8 are default values.
-    // Reference: http://msdn.microsoft.com/en-us/library/1s1byw77.aspx
-    static const size_t bucket_size = 4;
-    static const size_t min_buckets = 8;
-#endif  // STL_MSVC
-  };
-
-#ifdef STL_MSVC
-  typedef unordered_set<State*, StateHash> StateSet;
-#else  // !STL_MSVC
-  typedef unordered_set<State*, StateHash, StateEqual> StateSet;
-#endif  // STL_MSVC
-
-
- private:
-  // Special "firstbyte" values for a state.  (Values >= 0 denote actual bytes.)
-  enum {
-    kFbUnknown = -1,   // No analysis has been performed.
-    kFbMany = -2,      // Many bytes will lead out of this state.
-    kFbNone = -3,      // No bytes lead out of this state.
-  };
-
-  enum {
-    // Indices into start_ for unanchored searches.
-    // Add kStartAnchored for anchored searches.
-    kStartBeginText = 0,          // text at beginning of context
-    kStartBeginLine = 2,          // text at beginning of line
-    kStartAfterWordChar = 4,      // text follows a word character
-    kStartAfterNonWordChar = 6,   // text follows non-word character
-    kMaxStart = 8,
-
-    kStartAnchored = 1,
-  };
-
-  // Resets the DFA State cache, flushing all saved State* information.
-  // Releases and reacquires cache_mutex_ via cache_lock, so any
-  // State* existing before the call are not valid after the call.
-  // Use a StateSaver to preserve important states across the call.
-  // cache_mutex_.r <= L < mutex_
-  // After: cache_mutex_.w <= L < mutex_
-  void ResetCache(RWLocker* cache_lock);
-
-  // Looks up and returns the State corresponding to a Workq.
-  // L >= mutex_
-  State* WorkqToCachedState(Workq* q, uint flag);
-
-  // Looks up and returns a State matching the inst, ninst, and flag.
-  // L >= mutex_
-  State* CachedState(int* inst, int ninst, uint flag);
-
-  // Clear the cache entirely.
-  // Must hold cache_mutex_.w or be in destructor.
-  void ClearCache();
-
-  // Converts a State into a Workq: the opposite of WorkqToCachedState.
-  // L >= mutex_
-  static void StateToWorkq(State* s, Workq* q);
-
-  // Runs a State on a given byte, returning the next state.
-  State* RunStateOnByteUnlocked(State*, int);  // cache_mutex_.r <= L < mutex_
-  State* RunStateOnByte(State*, int);          // L >= mutex_
-
-  // Runs a Workq on a given byte followed by a set of empty-string flags,
-  // producing a new Workq in nq.  If a match instruction is encountered,
-  // sets *ismatch to true.
-  // L >= mutex_
-  void RunWorkqOnByte(Workq* q, Workq* nq,
-                      int c, uint flag, bool* ismatch,
-                      Prog::MatchKind kind);
-
-  // Runs a Workq on a set of empty-string flags, producing a new Workq in nq.
-  // L >= mutex_
-  void RunWorkqOnEmptyString(Workq* q, Workq* nq, uint flag);
-
-  // Adds the instruction id to the Workq, following empty arrows
-  // according to flag.
-  // L >= mutex_
-  void AddToQueue(Workq* q, int id, uint flag);
-
-  // For debugging, returns a text representation of State.
-  static string DumpState(State* state);
-
-  // For debugging, returns a text representation of a Workq.
-  static string DumpWorkq(Workq* q);
-
-  // Search parameters
-  struct SearchParams {
-    SearchParams(const StringPiece& text, const StringPiece& context,
-                 RWLocker* cache_lock)
-      : text(text), context(context),
-        anchored(false),
-        want_earliest_match(false),
-        run_forward(false),
-        start(NULL),
-        firstbyte(kFbUnknown),
-        cache_lock(cache_lock),
-        failed(false),
-        ep(NULL),
-        matches(NULL) { }
-
-    StringPiece text;
-    StringPiece context;
-    bool anchored;
-    bool want_earliest_match;
-    bool run_forward;
-    State* start;
-    int firstbyte;
-    RWLocker *cache_lock;
-    bool failed;     // "out" parameter: whether search gave up
-    const char* ep;  // "out" parameter: end pointer for match
-    vector<int>* matches;
-
-   private:
-    DISALLOW_COPY_AND_ASSIGN(SearchParams);
-  };
-
-  // Before each search, the parameters to Search are analyzed by
-  // AnalyzeSearch to determine the state in which to start and the
-  // "firstbyte" for that state, if any.
-  struct StartInfo {
-    StartInfo() : start(NULL), firstbyte(kFbUnknown) { }
-    State* start;
-    volatile int firstbyte;
-  };
-
-  // Fills in params->start and params->firstbyte using
-  // the other search parameters.  Returns true on success,
-  // false on failure.
-  // cache_mutex_.r <= L < mutex_
-  bool AnalyzeSearch(SearchParams* params);
-  bool AnalyzeSearchHelper(SearchParams* params, StartInfo* info, uint flags);
-
-  // The generic search loop, inlined to create specialized versions.
-  // cache_mutex_.r <= L < mutex_
-  // Might unlock and relock cache_mutex_ via params->cache_lock.
-  inline bool InlinedSearchLoop(SearchParams* params,
-                                bool have_firstbyte,
-                                bool want_earliest_match,
-                                bool run_forward);
-
-  // The specialized versions of InlinedSearchLoop.  The three letters
-  // at the ends of the name denote the true/false values used as the
-  // last three parameters of InlinedSearchLoop.
-  // cache_mutex_.r <= L < mutex_
-  // Might unlock and relock cache_mutex_ via params->cache_lock.
-  bool SearchFFF(SearchParams* params);
-  bool SearchFFT(SearchParams* params);
-  bool SearchFTF(SearchParams* params);
-  bool SearchFTT(SearchParams* params);
-  bool SearchTFF(SearchParams* params);
-  bool SearchTFT(SearchParams* params);
-  bool SearchTTF(SearchParams* params);
-  bool SearchTTT(SearchParams* params);
-
-  // The main search loop: calls an appropriate specialized version of
-  // InlinedSearchLoop.
-  // cache_mutex_.r <= L < mutex_
-  // Might unlock and relock cache_mutex_ via params->cache_lock.
-  bool FastSearchLoop(SearchParams* params);
-
-  // For debugging, a slow search loop that calls InlinedSearchLoop
-  // directly -- because the booleans passed are not constants, the
-  // loop is not specialized like the SearchFFF etc. versions, so it
-  // runs much more slowly.  Useful only for debugging.
-  // cache_mutex_.r <= L < mutex_
-  // Might unlock and relock cache_mutex_ via params->cache_lock.
-  bool SlowSearchLoop(SearchParams* params);
-
-  // Looks up bytes in bytemap_ but handles case c == kByteEndText too.
-  int ByteMap(int c) {
-    if (c == kByteEndText)
-      return prog_->bytemap_range();
-    return prog_->bytemap()[c];
-  }
-
-  // Constant after initialization.
-  Prog* prog_;              // The regular expression program to run.
-  Prog::MatchKind kind_;    // The kind of DFA.
-  bool init_failed_;        // initialization failed (out of memory)
-
-  Mutex mutex_;  // mutex_ >= cache_mutex_.r
-
-  // Scratch areas, protected by mutex_.
-  Workq* q0_;             // Two pre-allocated work queues.
-  Workq* q1_;
-  int* astack_;         // Pre-allocated stack for AddToQueue
-  int nastack_;
-
-  // State* cache.  Many threads use and add to the cache simultaneously,
-  // holding cache_mutex_ for reading and mutex_ (above) when adding.
-  // If the cache fills and needs to be discarded, the discarding is done
-  // while holding cache_mutex_ for writing, to avoid interrupting other
-  // readers.  Any State* pointers are only valid while cache_mutex_
-  // is held.
-  Mutex cache_mutex_;
-  int64 mem_budget_;       // Total memory budget for all States.
-  int64 state_budget_;     // Amount of memory remaining for new States.
-  StateSet state_cache_;   // All States computed so far.
-  StartInfo start_[kMaxStart];
-  bool cache_warned_;      // have printed to LOG(INFO) about the cache
-};
-
-// Shorthand for casting to uint8*.
-static inline const uint8* BytePtr(const void* v) {
-  return reinterpret_cast<const uint8*>(v);
-}
-
-// Work queues
-
-// Marks separate thread groups of different priority
-// in the work queue when in leftmost-longest matching mode.
-#define Mark (-1)
-
-// Internally, the DFA uses a sparse array of
-// program instruction pointers as a work queue.
-// In leftmost longest mode, marks separate sections
-// of workq that started executing at different
-// locations in the string (earlier locations first).
-class DFA::Workq : public SparseSet {
- public:
-  // Constructor: n is number of normal slots, maxmark number of mark slots.
-  Workq(int n, int maxmark) :
-    SparseSet(n+maxmark),
-    n_(n),
-    maxmark_(maxmark),
-    nextmark_(n),
-    last_was_mark_(true) {
-  }
-
-  bool is_mark(int i) { return i >= n_; }
-
-  int maxmark() { return maxmark_; }
-
-  void clear() {
-    SparseSet::clear();
-    nextmark_ = n_;
-  }
-
-  void mark() {
-    if (last_was_mark_)
-      return;
-    last_was_mark_ = false;
-    SparseSet::insert_new(nextmark_++);
-  }
-
-  int size() {
-    return n_ + maxmark_;
-  }
-
-  void insert(int id) {
-    if (contains(id))
-      return;
-    insert_new(id);
-  }
-
-  void insert_new(int id) {
-    last_was_mark_ = false;
-    SparseSet::insert_new(id);
-  }
-
- private:
-  int n_;                // size excluding marks
-  int maxmark_;          // maximum number of marks
-  int nextmark_;         // id of next mark
-  bool last_was_mark_;   // last inserted was mark
-  DISALLOW_COPY_AND_ASSIGN(Workq);
-};
-
-DFA::DFA(Prog* prog, Prog::MatchKind kind, int64 max_mem)
-  : prog_(prog),
-    kind_(kind),
-    init_failed_(false),
-    q0_(NULL),
-    q1_(NULL),
-    astack_(NULL),
-    mem_budget_(max_mem),
-    cache_warned_(false) {
-  if (DebugDFA)
-    fprintf(stderr, "\nkind %d\n%s\n", (int)kind_, prog_->DumpUnanchored().c_str());
-  int nmark = 0;
-  if (kind_ == Prog::kLongestMatch)
-    nmark = prog->size();
-  nastack_ = 2 * prog->size() + nmark;
-
-  // Account for space needed for DFA, q0, q1, astack.
-  mem_budget_ -= sizeof(DFA);
-  mem_budget_ -= (prog_->size() + nmark) *
-                 (sizeof(int)+sizeof(int)) * 2;  // q0, q1
-  mem_budget_ -= nastack_ * sizeof(int);  // astack
-  if (mem_budget_ < 0) {
-    LOG(INFO) << StringPrintf("DFA out of memory: prog size %d mem %lld",
-                              prog_->size(), max_mem);
-    init_failed_ = true;
-    return;
-  }
-
-  state_budget_ = mem_budget_;
-
-  // Make sure there is a reasonable amount of working room left.
-  // At minimum, the search requires room for two states in order
-  // to limp along, restarting frequently.  We'll get better performance
-  // if there is room for a larger number of states, say 20.
-  int64 one_state = sizeof(State) + (prog_->size()+nmark)*sizeof(int) +
-                    (prog_->bytemap_range()+1)*sizeof(State*);
-  if (state_budget_ < 20*one_state) {
-    LOG(INFO) << StringPrintf("DFA out of memory: prog size %d mem %lld",
-                              prog_->size(), max_mem);
-    init_failed_ = true;
-    return;
-  }
-
-  q0_ = new Workq(prog->size(), nmark);
-  q1_ = new Workq(prog->size(), nmark);
-  astack_ = new int[nastack_];
-}
-
-DFA::~DFA() {
-  delete q0_;
-  delete q1_;
-  delete[] astack_;
-  ClearCache();
-}
-
-// In the DFA state graph, s->next[c] == NULL means that the
-// state has not yet been computed and needs to be.  We need
-// a different special value to signal that s->next[c] is a
-// state that can never lead to a match (and thus the search
-// can be called off).  Hence DeadState.
-#define DeadState reinterpret_cast<State*>(1)
-
-// Signals that the rest of the string matches no matter what it is.
-#define FullMatchState reinterpret_cast<State*>(2)
-
-#define SpecialStateMax FullMatchState
-
-// Debugging printouts
-
-// For debugging, returns a string representation of the work queue.
-string DFA::DumpWorkq(Workq* q) {
-  string s;
-  const char* sep = "";
-  for (DFA::Workq::iterator it = q->begin(); it != q->end(); ++it) {
-    if (q->is_mark(*it)) {
-      StringAppendF(&s, "|");
-      sep = "";
-    } else {
-      StringAppendF(&s, "%s%d", sep, *it);
-      sep = ",";
-    }
-  }
-  return s;
-}
-
-// For debugging, returns a string representation of the state.
-string DFA::DumpState(State* state) {
-  if (state == NULL)
-    return "_";
-  if (state == DeadState)
-    return "X";
-  if (state == FullMatchState)
-    return "*";
-  string s;
-  const char* sep = "";
-  StringAppendF(&s, "(%p)", state);
-  for (int i = 0; i < state->ninst_; i++) {
-    if (state->inst_[i] == Mark) {
-      StringAppendF(&s, "|");
-      sep = "";
-    } else {
-      StringAppendF(&s, "%s%d", sep, state->inst_[i]);
-      sep = ",";
-    }
-  }
-  StringAppendF(&s, " flag=%#x", state->flag_);
-  return s;
-}
-
-//////////////////////////////////////////////////////////////////////
-//
-// DFA state graph construction.
-//
-// The DFA state graph is a heavily-linked collection of State* structures.
-// The state_cache_ is a set of all the State structures ever allocated,
-// so that if the same state is reached by two different paths,
-// the same State structure can be used.  This reduces allocation
-// requirements and also avoids duplication of effort across the two
-// identical states.
-//
-// A State is defined by an ordered list of instruction ids and a flag word.
-//
-// The choice of an ordered list of instructions differs from a typical
-// textbook DFA implementation, which would use an unordered set.
-// Textbook descriptions, however, only care about whether
-// the DFA matches, not where it matches in the text.  To decide where the
-// DFA matches, we need to mimic the behavior of the dominant backtracking
-// implementations like PCRE, which try one possible regular expression
-// execution, then another, then another, stopping when one of them succeeds.
-// The DFA execution tries these many executions in parallel, representing
-// each by an instruction id.  These pointers are ordered in the State.inst_
-// list in the same order that the executions would happen in a backtracking
-// search: if a match is found during execution of inst_[2], inst_[i] for i>=3
-// can be discarded.
-//
-// Textbooks also typically do not consider context-aware empty string operators
-// like ^ or $.  These are handled by the flag word, which specifies the set
-// of empty-string operators that should be matched when executing at the
-// current text position.  These flag bits are defined in prog.h.
-// The flag word also contains two DFA-specific bits: kFlagMatch if the state
-// is a matching state (one that reached a kInstMatch in the program)
-// and kFlagLastWord if the last processed byte was a word character, for the
-// implementation of \B and \b.
-//
-// The flag word also contains, shifted up 16 bits, the bits looked for by
-// any kInstEmptyWidth instructions in the state.  These provide a useful
-// summary indicating when new flags might be useful.
-//
-// The permanent representation of a State's instruction ids is just an array,
-// but while a state is being analyzed, these instruction ids are represented
-// as a Workq, which is an array that allows iteration in insertion order.
-
-// NOTE(rsc): The choice of State construction determines whether the DFA
-// mimics backtracking implementations (so-called leftmost first matching) or
-// traditional DFA implementations (so-called leftmost longest matching as
-// prescribed by POSIX).  This implementation chooses to mimic the
-// backtracking implementations, because we want to replace PCRE.  To get
-// POSIX behavior, the states would need to be considered not as a simple
-// ordered list of instruction ids, but as a list of unordered sets of instruction
-// ids.  A match by a state in one set would inhibit the running of sets
-// farther down the list but not other instruction ids in the same set.  Each
-// set would correspond to matches beginning at a given point in the string.
-// This is implemented by separating different sets with Mark pointers.
-
-// Looks in the State cache for a State matching q, flag.
-// If one is found, returns it.  If one is not found, allocates one,
-// inserts it in the cache, and returns it.
-DFA::State* DFA::WorkqToCachedState(Workq* q, uint flag) {
-  if (DEBUG_MODE)
-    mutex_.AssertHeld();
-
-  // Construct array of instruction ids for the new state.
-  // Only ByteRange, EmptyWidth, and Match instructions are useful to keep:
-  // those are the only operators with any effect in
-  // RunWorkqOnEmptyString or RunWorkqOnByte.
-  int* inst = new int[q->size()];
-  int n = 0;
-  uint needflags = 0;     // flags needed by kInstEmptyWidth instructions
-  bool sawmatch = false;  // whether queue contains guaranteed kInstMatch
-  bool sawmark = false;  // whether queue contains a Mark
-  if (DebugDFA)
-    fprintf(stderr, "WorkqToCachedState %s [%#x]", DumpWorkq(q).c_str(), flag);
-  for (Workq::iterator it = q->begin(); it != q->end(); ++it) {
-    int id = *it;
-    if (sawmatch && (kind_ == Prog::kFirstMatch || q->is_mark(id)))
-      break;
-    if (q->is_mark(id)) {
-      if (n > 0 && inst[n-1] != Mark) {
-        sawmark = true;
-        inst[n++] = Mark;
-      }
-      continue;
-    }
-    Prog::Inst* ip = prog_->inst(id);
-    switch (ip->opcode()) {
-      case kInstAltMatch:
-        // This state will continue to a match no matter what
-        // the rest of the input is.  If it is the highest priority match
-        // being considered, return the special FullMatchState
-        // to indicate that it's all matches from here out.
-        if (kind_ != Prog::kManyMatch &&
-            (kind_ != Prog::kFirstMatch ||
-             (it == q->begin() && ip->greedy(prog_))) &&
-            (kind_ != Prog::kLongestMatch || !sawmark) &&
-            (flag & kFlagMatch)) {
-          delete[] inst;
-          if (DebugDFA)
-            fprintf(stderr, " -> FullMatchState\n");
-          return FullMatchState;
-        }
-        // Fall through.
-      case kInstByteRange:    // These are useful.
-      case kInstEmptyWidth:
-      case kInstMatch:
-      case kInstAlt:          // Not useful, but necessary [*]
-        inst[n++] = *it;
-        if (ip->opcode() == kInstEmptyWidth)
-          needflags |= ip->empty();
-        if (ip->opcode() == kInstMatch && !prog_->anchor_end())
-          sawmatch = true;
-        break;
-
-      default:                // The rest are not.
-        break;
-    }
-
-    // [*] kInstAlt would seem useless to record in a state, since
-    // we've already followed both its arrows and saved all the
-    // interesting states we can reach from there.  The problem
-    // is that one of the empty-width instructions might lead
-    // back to the same kInstAlt (if an empty-width operator is starred),
-    // producing a different evaluation order depending on whether
-    // we keep the kInstAlt to begin with.  Sigh.
-    // A specific case that this affects is /(^|a)+/ matching "a".
-    // If we don't save the kInstAlt, we will match the whole "a" (0,1)
-    // but in fact the correct leftmost-first match is the leading "" (0,0).
-  }
-  DCHECK_LE(n, q->size());
-  if (n > 0 && inst[n-1] == Mark)
-    n--;
-
-  // If there are no empty-width instructions waiting to execute,
-  // then the extra flag bits will not be used, so there is no
-  // point in saving them.  (Discarding them reduces the number
-  // of distinct states.)
-  if (needflags == 0)
-    flag &= kFlagMatch;
-
-  // NOTE(rsc): The code above cannot do flag &= needflags,
-  // because if the right flags were present to pass the current
-  // kInstEmptyWidth instructions, new kInstEmptyWidth instructions
-  // might be reached that in turn need different flags.
-  // The only sure thing is that if there are no kInstEmptyWidth
-  // instructions at all, no flags will be needed.
-  // We could do the extra work to figure out the full set of
-  // possibly needed flags by exploring past the kInstEmptyWidth
-  // instructions, but the check above -- are any flags needed
-  // at all? -- handles the most common case.  More fine-grained
-  // analysis can only be justified by measurements showing that
-  // too many redundant states are being allocated.
-
-  // If there are no Insts in the list, it's a dead state,
-  // which is useful to signal with a special pointer so that
-  // the execution loop can stop early.  This is only okay
-  // if the state is *not* a matching state.
-  if (n == 0 && flag == 0) {
-    delete[] inst;
-    if (DebugDFA)
-      fprintf(stderr, " -> DeadState\n");
-    return DeadState;
-  }
-
-  // If we're in longest match mode, the state is a sequence of
-  // unordered state sets separated by Marks.  Sort each set
-  // to canonicalize, to reduce the number of distinct sets stored.
-  if (kind_ == Prog::kLongestMatch) {
-    int* ip = inst;
-    int* ep = ip + n;
-    while (ip < ep) {
-      int* markp = ip;
-      while (markp < ep && *markp != Mark)
-        markp++;
-      sort(ip, markp);
-      if (markp < ep)
-        markp++;
-      ip = markp;
-    }
-  }
-
-  // Save the needed empty-width flags in the top bits for use later.
-  flag |= needflags << kFlagNeedShift;
-
-  State* state = CachedState(inst, n, flag);
-  delete[] inst;
-  return state;
-}
-
-// Looks in the State cache for a State matching inst, ninst, flag.
-// If one is found, returns it.  If one is not found, allocates one,
-// inserts it in the cache, and returns it.
-DFA::State* DFA::CachedState(int* inst, int ninst, uint flag) {
-  if (DEBUG_MODE)
-    mutex_.AssertHeld();
-
-  // Look in the cache for a pre-existing state.
-  State state = { inst, ninst, flag, NULL };
-  StateSet::iterator it = state_cache_.find(&state);
-  if (it != state_cache_.end()) {
-    if (DebugDFA)
-      fprintf(stderr, " -cached-> %s\n", DumpState(*it).c_str());
-    return *it;
-  }
-
-  // Must have enough memory for new state.
-  // In addition to what we're going to allocate,
-  // the state cache hash table seems to incur about 32 bytes per
-  // State*, empirically.
-  const int kStateCacheOverhead = 32;
-  int nnext = prog_->bytemap_range() + 1;  // + 1 for kByteEndText slot
-  int mem = sizeof(State) + nnext*sizeof(State*) + ninst*sizeof(int);
-  if (mem_budget_ < mem + kStateCacheOverhead) {
-    mem_budget_ = -1;
-    return NULL;
-  }
-  mem_budget_ -= mem + kStateCacheOverhead;
-
-  // Allocate new state, along with room for next and inst.
-  char* space = new char[mem];
-  State* s = reinterpret_cast<State*>(space);
-  s->next_ = reinterpret_cast<State**>(s + 1);
-  s->inst_ = reinterpret_cast<int*>(s->next_ + nnext);
-  memset(s->next_, 0, nnext*sizeof s->next_[0]);
-  memmove(s->inst_, inst, ninst*sizeof s->inst_[0]);
-  s->ninst_ = ninst;
-  s->flag_ = flag;
-  if (DebugDFA)
-    fprintf(stderr, " -> %s\n", DumpState(s).c_str());
-
-  // Put state in cache and return it.
-  state_cache_.insert(s);
-  return s;
-}
-
-// Clear the cache.  Must hold cache_mutex_.w or be in destructor.
-void DFA::ClearCache() {
-  // In case state_cache_ doesn't support deleting entries
-  // during iteration, copy into a vector and then delete.
-  vector<State*> v;
-  v.reserve(state_cache_.size());
-  for (StateSet::iterator it = state_cache_.begin();
-       it != state_cache_.end(); ++it)
-    v.push_back(*it);
-  state_cache_.clear();
-  for (size_t i = 0; i < v.size(); i++)
-    delete[] reinterpret_cast<const char*>(v[i]);
-}
-
-// Copies insts in state s to the work queue q.
-void DFA::StateToWorkq(State* s, Workq* q) {
-  q->clear();
-  for (int i = 0; i < s->ninst_; i++) {
-    if (s->inst_[i] == Mark)
-      q->mark();
-    else
-      q->insert_new(s->inst_[i]);
-  }
-}
-
-// Adds ip to the work queue, following empty arrows according to flag
-// and expanding kInstAlt instructions (two-target gotos).
-void DFA::AddToQueue(Workq* q, int id, uint flag) {
-
-  // Use astack_ to hold our stack of states yet to process.
-  // It is sized to have room for nastack_ == 2*prog->size() + nmark
-  // instructions, which is enough: each instruction can be
-  // processed by the switch below only once, and the processing
-  // pushes at most two instructions plus maybe a mark.
-  // (If we're using marks, nmark == prog->size(); otherwise nmark == 0.)
-  int* stk = astack_;
-  int nstk = 0;
-
-  stk[nstk++] = id;
-  while (nstk > 0) {
-    DCHECK_LE(nstk, nastack_);
-    id = stk[--nstk];
-
-    if (id == Mark) {
-      q->mark();
-      continue;
-    }
-
-    if (id == 0)
-      continue;
-
-    // If ip is already on the queue, nothing to do.
-    // Otherwise add it.  We don't actually keep all the ones
-    // that get added -- for example, kInstAlt is ignored
-    // when on a work queue -- but adding all ip's here
-    // increases the likelihood of q->contains(id),
-    // reducing the amount of duplicated work.
-    if (q->contains(id))
-      continue;
-    q->insert_new(id);
-
-    // Process instruction.
-    Prog::Inst* ip = prog_->inst(id);
-    switch (ip->opcode()) {
-      case kInstFail:       // can't happen: discarded above
-        break;
-
-      case kInstByteRange:  // just save these on the queue
-      case kInstMatch:
-        break;
-
-      case kInstCapture:    // DFA treats captures as no-ops.
-      case kInstNop:
-        stk[nstk++] = ip->out();
-        break;
-
-      case kInstAlt:        // two choices: expand both, in order
-      case kInstAltMatch:
-        // Want to visit out then out1, so push on stack in reverse order.
-        // This instruction is the [00-FF]* loop at the beginning of
-        // a leftmost-longest unanchored search, separate out from out1
-        // with a Mark, so that out1's threads (which will start farther
-        // to the right in the string being searched) are lower priority
-        // than the current ones.
-        stk[nstk++] = ip->out1();
-        if (q->maxmark() > 0 &&
-            id == prog_->start_unanchored() && id != prog_->start())
-          stk[nstk++] = Mark;
-        stk[nstk++] = ip->out();
-        break;
-
-      case kInstEmptyWidth:
-        // Continue on if we have all the right flag bits.
-        if (ip->empty() & ~flag)
-          break;
-        stk[nstk++] = ip->out();
-        break;
-    }
-  }
-}
-
-// Running of work queues.  In the work queue, order matters:
-// the queue is sorted in priority order.  If instruction i comes before j,
-// then the instructions that i produces during the run must come before
-// the ones that j produces.  In order to keep this invariant, all the
-// work queue runners have to take an old queue to process and then
-// also a new queue to fill in.  It's not acceptable to add to the end of
-// an existing queue, because new instructions will not end up in the
-// correct position.
-
-// Runs the work queue, processing the empty strings indicated by flag.
-// For example, flag == kEmptyBeginLine|kEmptyEndLine means to match
-// both ^ and $.  It is important that callers pass all flags at once:
-// processing both ^ and $ is not the same as first processing only ^
-// and then processing only $.  Doing the two-step sequence won't match
-// ^$^$^$ but processing ^ and $ simultaneously will (and is the behavior
-// exhibited by existing implementations).
-void DFA::RunWorkqOnEmptyString(Workq* oldq, Workq* newq, uint flag) {
-  newq->clear();
-  for (Workq::iterator i = oldq->begin(); i != oldq->end(); ++i) {
-    if (oldq->is_mark(*i))
-      AddToQueue(newq, Mark, flag);
-    else
-      AddToQueue(newq, *i, flag);
-  }
-}
-
-// Runs the work queue, processing the single byte c followed by any empty
-// strings indicated by flag.  For example, c == 'a' and flag == kEmptyEndLine,
-// means to match c$.  Sets the bool *ismatch to true if the end of the
-// regular expression program has been reached (the regexp has matched).
-void DFA::RunWorkqOnByte(Workq* oldq, Workq* newq,
-                         int c, uint flag, bool* ismatch,
-                         Prog::MatchKind kind) {
-  if (DEBUG_MODE)
-    mutex_.AssertHeld();
-
-  newq->clear();
-  for (Workq::iterator i = oldq->begin(); i != oldq->end(); ++i) {
-    if (oldq->is_mark(*i)) {
-      if (*ismatch)
-        return;
-      newq->mark();
-      continue;
-    }
-    int id = *i;
-    Prog::Inst* ip = prog_->inst(id);
-    switch (ip->opcode()) {
-      case kInstFail:        // never succeeds
-      case kInstCapture:     // already followed
-      case kInstNop:         // already followed
-      case kInstAlt:         // already followed
-      case kInstAltMatch:    // already followed
-      case kInstEmptyWidth:  // already followed
-        break;
-
-      case kInstByteRange:   // can follow if c is in range
-        if (ip->Matches(c))
-          AddToQueue(newq, ip->out(), flag);
-        break;
-
-      case kInstMatch:
-        if (prog_->anchor_end() && c != kByteEndText)
-          break;
-        *ismatch = true;
-        if (kind == Prog::kFirstMatch) {
-          // Can stop processing work queue since we found a match.
-          return;
-        }
-        break;
-    }
-  }
-
-  if (DebugDFA)
-    fprintf(stderr, "%s on %d[%#x] -> %s [%d]\n", DumpWorkq(oldq).c_str(),
-            c, flag, DumpWorkq(newq).c_str(), *ismatch);
-}
-
-// Processes input byte c in state, returning new state.
-// Caller does not hold mutex.
-DFA::State* DFA::RunStateOnByteUnlocked(State* state, int c) {
-  // Keep only one RunStateOnByte going
-  // even if the DFA is being run by multiple threads.
-  MutexLock l(&mutex_);
-  return RunStateOnByte(state, c);
-}
-
-// Processes input byte c in state, returning new state.
-DFA::State* DFA::RunStateOnByte(State* state, int c) {
-  if (DEBUG_MODE)
-    mutex_.AssertHeld();
-  if (state <= SpecialStateMax) {
-    if (state == FullMatchState) {
-      // It is convenient for routines like PossibleMatchRange
-      // if we implement RunStateOnByte for FullMatchState:
-      // once you get into this state you never get out,
-      // so it's pretty easy.
-      return FullMatchState;
-    }
-    if (state == DeadState) {
-      LOG(DFATAL) << "DeadState in RunStateOnByte";
-      return NULL;
-    }
-    if (state == NULL) {
-      LOG(DFATAL) << "NULL state in RunStateOnByte";
-      return NULL;
-    }
-    LOG(DFATAL) << "Unexpected special state in RunStateOnByte";
-    return NULL;
-  }
-
-  // If someone else already computed this, return it.
-  State* ns;
-  ATOMIC_LOAD_CONSUME(ns, &state->next_[ByteMap(c)]);
-  if (ns != NULL)
-    return ns;
-
-  // Convert state into Workq.
-  StateToWorkq(state, q0_);
-
-  // Flags marking the kinds of empty-width things (^ $ etc)
-  // around this byte.  Before the byte we have the flags recorded
-  // in the State structure itself.  After the byte we have
-  // nothing yet (but that will change: read on).
-  uint needflag = state->flag_ >> kFlagNeedShift;
-  uint beforeflag = state->flag_ & kFlagEmptyMask;
-  uint oldbeforeflag = beforeflag;
-  uint afterflag = 0;
-
-  if (c == '\n') {
-    // Insert implicit $ and ^ around \n
-    beforeflag |= kEmptyEndLine;
-    afterflag |= kEmptyBeginLine;
-  }
-
-  if (c == kByteEndText) {
-    // Insert implicit $ and \z before the fake "end text" byte.
-    beforeflag |= kEmptyEndLine | kEmptyEndText;
-  }
-
-  // The state flag kFlagLastWord says whether the last
-  // byte processed was a word character.  Use that info to
-  // insert empty-width (non-)word boundaries.
-  bool islastword = (state->flag_ & kFlagLastWord) != 0;
-  bool isword = (c != kByteEndText && Prog::IsWordChar(static_cast<uint8>(c)));
-  if (isword == islastword)
-    beforeflag |= kEmptyNonWordBoundary;
-  else
-    beforeflag |= kEmptyWordBoundary;
-
-  // Okay, finally ready to run.
-  // Only useful to rerun on empty string if there are new, useful flags.
-  if (beforeflag & ~oldbeforeflag & needflag) {
-    RunWorkqOnEmptyString(q0_, q1_, beforeflag);
-    swap(q0_, q1_);
-  }
-  bool ismatch = false;
-  RunWorkqOnByte(q0_, q1_, c, afterflag, &ismatch, kind_);
-
-  // Most of the time, we build the state from the output of
-  // RunWorkqOnByte, so swap q0_ and q1_ here.  However, so that
-  // RE2::Set can tell exactly which match instructions
-  // contributed to the match, don't swap if c is kByteEndText.
-  // The resulting state wouldn't be correct for further processing
-  // of the string, but we're at the end of the text so that's okay.
-  // Leaving q0_ alone preseves the match instructions that led to
-  // the current setting of ismatch.
-  if (c != kByteEndText || kind_ != Prog::kManyMatch)
-    swap(q0_, q1_);
-
-  // Save afterflag along with ismatch and isword in new state.
-  uint flag = afterflag;
-  if (ismatch)
-    flag |= kFlagMatch;
-  if (isword)
-    flag |= kFlagLastWord;
-
-  ns = WorkqToCachedState(q0_, flag);
-
-  // Flush ns before linking to it.
-  // Write barrier before updating state->next_ so that the
-  // main search loop can proceed without any locking, for speed.
-  // (Otherwise it would need one mutex operation per input byte.)
-  ATOMIC_STORE_RELEASE(&state->next_[ByteMap(c)], ns);
-  return ns;
-}
-
-
-//////////////////////////////////////////////////////////////////////
-// DFA cache reset.
-
-// Reader-writer lock helper.
-//
-// The DFA uses a reader-writer mutex to protect the state graph itself.
-// Traversing the state graph requires holding the mutex for reading,
-// and discarding the state graph and starting over requires holding the
-// lock for writing.  If a search needs to expand the graph but is out
-// of memory, it will need to drop its read lock and then acquire the
-// write lock.  Since it cannot then atomically downgrade from write lock
-// to read lock, it runs the rest of the search holding the write lock.
-// (This probably helps avoid repeated contention, but really the decision
-// is forced by the Mutex interface.)  It's a bit complicated to keep
-// track of whether the lock is held for reading or writing and thread
-// that through the search, so instead we encapsulate it in the RWLocker
-// and pass that around.
-
-class DFA::RWLocker {
- public:
-  explicit RWLocker(Mutex* mu);
-  ~RWLocker();
-
-  // If the lock is only held for reading right now,
-  // drop the read lock and re-acquire for writing.
-  // Subsequent calls to LockForWriting are no-ops.
-  // Notice that the lock is *released* temporarily.
-  void LockForWriting();
-
-  // Returns whether the lock is already held for writing.
-  bool IsLockedForWriting() {
-    return writing_;
-  }
-
- private:
-  Mutex* mu_;
-  bool writing_;
-
-  DISALLOW_COPY_AND_ASSIGN(RWLocker);
-};
-
-DFA::RWLocker::RWLocker(Mutex* mu)
-  : mu_(mu), writing_(false) {
-
-  mu_->ReaderLock();
-}
-
-// This function is marked as NO_THREAD_SAFETY_ANALYSIS because the annotations
-// does not support lock upgrade.
-void DFA::RWLocker::LockForWriting() NO_THREAD_SAFETY_ANALYSIS {
-  if (!writing_) {
-    mu_->ReaderUnlock();
-    mu_->Lock();
-    writing_ = true;
-  }
-}
-
-DFA::RWLocker::~RWLocker() {
-  if (writing_)
-    mu_->WriterUnlock();
-  else
-    mu_->ReaderUnlock();
-}
-
-
-// When the DFA's State cache fills, we discard all the states in the
-// cache and start over.  Many threads can be using and adding to the
-// cache at the same time, so we synchronize using the cache_mutex_
-// to keep from stepping on other threads.  Specifically, all the
-// threads using the current cache hold cache_mutex_ for reading.
-// When a thread decides to flush the cache, it drops cache_mutex_
-// and then re-acquires it for writing.  That ensures there are no
-// other threads accessing the cache anymore.  The rest of the search
-// runs holding cache_mutex_ for writing, avoiding any contention
-// with or cache pollution caused by other threads.
-
-void DFA::ResetCache(RWLocker* cache_lock) {
-  // Re-acquire the cache_mutex_ for writing (exclusive use).
-  bool was_writing = cache_lock->IsLockedForWriting();
-  cache_lock->LockForWriting();
-
-  // If we already held cache_mutex_ for writing, it means
-  // this invocation of Search() has already reset the
-  // cache once already.  That's a pretty clear indication
-  // that the cache is too small.  Warn about that, once.
-  // TODO(rsc): Only warn if state_cache_.size() < some threshold.
-  if (was_writing && !cache_warned_) {
-    LOG(INFO) << "DFA memory cache could be too small: "
-              << "only room for " << state_cache_.size() << " states.";
-    cache_warned_ = true;
-  }
-
-  // Clear the cache, reset the memory budget.
-  for (int i = 0; i < kMaxStart; i++) {
-    start_[i].start = NULL;
-    start_[i].firstbyte = kFbUnknown;
-  }
-  ClearCache();
-  mem_budget_ = state_budget_;
-}
-
-// Typically, a couple States do need to be preserved across a cache
-// reset, like the State at the current point in the search.
-// The StateSaver class helps keep States across cache resets.
-// It makes a copy of the state's guts outside the cache (before the reset)
-// and then can be asked, after the reset, to recreate the State
-// in the new cache.  For example, in a DFA method ("this" is a DFA):
-//
-//   StateSaver saver(this, s);
-//   ResetCache(cache_lock);
-//   s = saver.Restore();
-//
-// The saver should always have room in the cache to re-create the state,
-// because resetting the cache locks out all other threads, and the cache
-// is known to have room for at least a couple states (otherwise the DFA
-// constructor fails).
-
-class DFA::StateSaver {
- public:
-  explicit StateSaver(DFA* dfa, State* state);
-  ~StateSaver();
-
-  // Recreates and returns a state equivalent to the
-  // original state passed to the constructor.
-  // Returns NULL if the cache has filled, but
-  // since the DFA guarantees to have room in the cache
-  // for a couple states, should never return NULL
-  // if used right after ResetCache.
-  State* Restore();
-
- private:
-  DFA* dfa_;         // the DFA to use
-  int* inst_;        // saved info from State
-  int ninst_;
-  uint flag_;
-  bool is_special_;  // whether original state was special
-  State* special_;   // if is_special_, the original state
-
-  DISALLOW_COPY_AND_ASSIGN(StateSaver);
-};
-
-DFA::StateSaver::StateSaver(DFA* dfa, State* state) {
-  dfa_ = dfa;
-  if (state <= SpecialStateMax) {
-    inst_ = NULL;
-    ninst_ = 0;
-    flag_ = 0;
-    is_special_ = true;
-    special_ = state;
-    return;
-  }
-  is_special_ = false;
-  special_ = NULL;
-  flag_ = state->flag_;
-  ninst_ = state->ninst_;
-  inst_ = new int[ninst_];
-  memmove(inst_, state->inst_, ninst_*sizeof inst_[0]);
-}
-
-DFA::StateSaver::~StateSaver() {
-  if (!is_special_)
-    delete[] inst_;
-}
-
-DFA::State* DFA::StateSaver::Restore() {
-  if (is_special_)
-    return special_;
-  MutexLock l(&dfa_->mutex_);
-  State* s = dfa_->CachedState(inst_, ninst_, flag_);
-  if (s == NULL)
-    LOG(DFATAL) << "StateSaver failed to restore state.";
-  return s;
-}
-
-
-//////////////////////////////////////////////////////////////////////
-//
-// DFA execution.
-//
-// The basic search loop is easy: start in a state s and then for each
-// byte c in the input, s = s->next[c].
-//
-// This simple description omits a few efficiency-driven complications.
-//
-// First, the State graph is constructed incrementally: it is possible
-// that s->next[c] is null, indicating that that state has not been
-// fully explored.  In this case, RunStateOnByte must be invoked to
-// determine the next state, which is cached in s->next[c] to save
-// future effort.  An alternative reason for s->next[c] to be null is
-// that the DFA has reached a so-called "dead state", in which any match
-// is no longer possible.  In this case RunStateOnByte will return NULL
-// and the processing of the string can stop early.
-//
-// Second, a 256-element pointer array for s->next_ makes each State
-// quite large (2kB on 64-bit machines).  Instead, dfa->bytemap_[]
-// maps from bytes to "byte classes" and then next_ only needs to have
-// as many pointers as there are byte classes.  A byte class is simply a
-// range of bytes that the regexp never distinguishes between.
-// A regexp looking for a[abc] would have four byte ranges -- 0 to 'a'-1,
-// 'a', 'b' to 'c', and 'c' to 0xFF.  The bytemap slows us a little bit
-// but in exchange we typically cut the size of a State (and thus our
-// memory footprint) by about 5-10x.  The comments still refer to
-// s->next[c] for simplicity, but code should refer to s->next_[bytemap_[c]].
-//
-// Third, it is common for a DFA for an unanchored match to begin in a
-// state in which only one particular byte value can take the DFA to a
-// different state.  That is, s->next[c] != s for only one c.  In this
-// situation, the DFA can do better than executing the simple loop.
-// Instead, it can call memchr to search very quickly for the byte c.
-// Whether the start state has this property is determined during a
-// pre-compilation pass, and if so, the byte b is passed to the search
-// loop as the "firstbyte" argument, along with a boolean "have_firstbyte".
-//
-// Fourth, the desired behavior is to search for the leftmost-best match
-// (approximately, the same one that Perl would find), which is not
-// necessarily the match ending earliest in the string.  Each time a
-// match is found, it must be noted, but the DFA must continue on in
-// hope of finding a higher-priority match.  In some cases, the caller only
-// cares whether there is any match at all, not which one is found.
-// The "want_earliest_match" flag causes the search to stop at the first
-// match found.
-//
-// Fifth, one algorithm that uses the DFA needs it to run over the
-// input string backward, beginning at the end and ending at the beginning.
-// Passing false for the "run_forward" flag causes the DFA to run backward.
-//
-// The checks for these last three cases, which in a naive implementation
-// would be performed once per input byte, slow the general loop enough
-// to merit specialized versions of the search loop for each of the
-// eight possible settings of the three booleans.  Rather than write
-// eight different functions, we write one general implementation and then
-// inline it to create the specialized ones.
-//
-// Note that matches are delayed by one byte, to make it easier to
-// accomodate match conditions depending on the next input byte (like $ and \b).
-// When s->next[c]->IsMatch(), it means that there is a match ending just
-// *before* byte c.
-
-// The generic search loop.  Searches text for a match, returning
-// the pointer to the end of the chosen match, or NULL if no match.
-// The bools are equal to the same-named variables in params, but
-// making them function arguments lets the inliner specialize
-// this function to each combination (see two paragraphs above).
-inline bool DFA::InlinedSearchLoop(SearchParams* params,
-                                   bool have_firstbyte,
-                                   bool want_earliest_match,
-                                   bool run_forward) {
-  State* start = params->start;
-  const uint8* bp = BytePtr(params->text.begin());  // start of text
-  const uint8* p = bp;                              // text scanning point
-  const uint8* ep = BytePtr(params->text.end());    // end of text
-  const uint8* resetp = NULL;                       // p at last cache reset
-  if (!run_forward)
-    swap(p, ep);
-
-  const uint8* bytemap = prog_->bytemap();
-  const uint8* lastmatch = NULL;   // most recent matching position in text
-  bool matched = false;
-  State* s = start;
-
-  if (s->IsMatch()) {
-    matched = true;
-    lastmatch = p;
-    if (want_earliest_match) {
-      params->ep = reinterpret_cast<const char*>(lastmatch);
-      return true;
-    }
-  }
-
-  while (p != ep) {
-    if (DebugDFA)
-      fprintf(stderr, "@%d: %s\n", static_cast<int>(p - bp),
-              DumpState(s).c_str());
-    if (have_firstbyte && s == start) {
-      // In start state, only way out is to find firstbyte,
-      // so use optimized assembly in memchr to skip ahead.
-      // If firstbyte isn't found, we can skip to the end
-      // of the string.
-      if (run_forward) {
-        if ((p = BytePtr(memchr(p, params->firstbyte, ep - p))) == NULL) {
-          p = ep;
-          break;
-        }
-      } else {
-        if ((p = BytePtr(memrchr(ep, params->firstbyte, p - ep))) == NULL) {
-          p = ep;
-          break;
-        }
-        p++;
-      }
-    }
-
-    int c;
-    if (run_forward)
-      c = *p++;
-    else
-      c = *--p;
-
-    // Note that multiple threads might be consulting
-    // s->next_[bytemap[c]] simultaneously.
-    // RunStateOnByte takes care of the appropriate locking,
-    // including a memory barrier so that the unlocked access
-    // (sometimes known as "double-checked locking") is safe.
-    // The alternative would be either one DFA per thread
-    // or one mutex operation per input byte.
-    //
-    // ns == DeadState means the state is known to be dead
-    // (no more matches are possible).
-    // ns == NULL means the state has not yet been computed
-    // (need to call RunStateOnByteUnlocked).
-    // RunStateOnByte returns ns == NULL if it is out of memory.
-    // ns == FullMatchState means the rest of the string matches.
-    //
-    // Okay to use bytemap[] not ByteMap() here, because
-    // c is known to be an actual byte and not kByteEndText.
-
-    State* ns;
-    ATOMIC_LOAD_CONSUME(ns, &s->next_[bytemap[c]]);
-    if (ns == NULL) {
-      ns = RunStateOnByteUnlocked(s, c);
-      if (ns == NULL) {
-        // After we reset the cache, we hold cache_mutex exclusively,
-        // so if resetp != NULL, it means we filled the DFA state
-        // cache with this search alone (without any other threads).
-        // Benchmarks show that doing a state computation on every
-        // byte runs at about 0.2 MB/s, while the NFA (nfa.cc) can do the
-        // same at about 2 MB/s.  Unless we're processing an average
-        // of 10 bytes per state computation, fail so that RE2 can
-        // fall back to the NFA.
-        if (FLAGS_re2_dfa_bail_when_slow && resetp != NULL &&
-            static_cast<unsigned long>(p - resetp) < 10*state_cache_.size()) {
-          params->failed = true;
-          return false;
-        }
-        resetp = p;
-
-        // Prepare to save start and s across the reset.
-        StateSaver save_start(this, start);
-        StateSaver save_s(this, s);
-
-        // Discard all the States in the cache.
-        ResetCache(params->cache_lock);
-
-        // Restore start and s so we can continue.
-        if ((start = save_start.Restore()) == NULL ||
-            (s = save_s.Restore()) == NULL) {
-          // Restore already did LOG(DFATAL).
-          params->failed = true;
-          return false;
-        }
-        ns = RunStateOnByteUnlocked(s, c);
-        if (ns == NULL) {
-          LOG(DFATAL) << "RunStateOnByteUnlocked failed after ResetCache";
-          params->failed = true;
-          return false;
-        }
-      }
-    }
-    if (ns <= SpecialStateMax) {
-      if (ns == DeadState) {
-        params->ep = reinterpret_cast<const char*>(lastmatch);
-        return matched;
-      }
-      // FullMatchState
-      params->ep = reinterpret_cast<const char*>(ep);
-      return true;
-    }
-    s = ns;
-
-    if (s->IsMatch()) {
-      matched = true;
-      // The DFA notices the match one byte late,
-      // so adjust p before using it in the match.
-      if (run_forward)
-        lastmatch = p - 1;
-      else
-        lastmatch = p + 1;
-      if (DebugDFA)
-        fprintf(stderr, "match @%d! [%s]\n",
-                static_cast<int>(lastmatch - bp),
-                DumpState(s).c_str());
-
-      if (want_earliest_match) {
-        params->ep = reinterpret_cast<const char*>(lastmatch);
-        return true;
-      }
-    }
-  }
-
-  // Process one more byte to see if it triggers a match.
-  // (Remember, matches are delayed one byte.)
-  int lastbyte;
-  if (run_forward) {
-    if (params->text.end() == params->context.end())
-      lastbyte = kByteEndText;
-    else
-      lastbyte = params->text.end()[0] & 0xFF;
-  } else {
-    if (params->text.begin() == params->context.begin())
-      lastbyte = kByteEndText;
-    else
-      lastbyte = params->text.begin()[-1] & 0xFF;
-  }
-
-  State* ns;
-  ATOMIC_LOAD_CONSUME(ns, &s->next_[ByteMap(lastbyte)]);
-  if (ns == NULL) {
-    ns = RunStateOnByteUnlocked(s, lastbyte);
-    if (ns == NULL) {
-      StateSaver save_s(this, s);
-      ResetCache(params->cache_lock);
-      if ((s = save_s.Restore()) == NULL) {
-        params->failed = true;
-        return false;
-      }
-      ns = RunStateOnByteUnlocked(s, lastbyte);
-      if (ns == NULL) {
-        LOG(DFATAL) << "RunStateOnByteUnlocked failed after Reset";
-        params->failed = true;
-        return false;
-      }
-    }
-  }
-  s = ns;
-  if (DebugDFA)
-    fprintf(stderr, "@_: %s\n", DumpState(s).c_str());
-  if (s == FullMatchState) {
-    params->ep = reinterpret_cast<const char*>(ep);
-    return true;
-  }
-  if (s > SpecialStateMax && s->IsMatch()) {
-    matched = true;
-    lastmatch = p;
-    if (params->matches && kind_ == Prog::kManyMatch) {
-      vector<int>* v = params->matches;
-      v->clear();
-      for (int i = 0; i < s->ninst_; i++) {
-        Prog::Inst* ip = prog_->inst(s->inst_[i]);
-        if (ip->opcode() == kInstMatch)
-          v->push_back(ip->match_id());
-      }
-    }
-    if (DebugDFA)
-      fprintf(stderr, "match @%d! [%s]\n", static_cast<int>(lastmatch - bp),
-              DumpState(s).c_str());
-  }
-  params->ep = reinterpret_cast<const char*>(lastmatch);
-  return matched;
-}
-
-// Inline specializations of the general loop.
-bool DFA::SearchFFF(SearchParams* params) {
-  return InlinedSearchLoop(params, 0, 0, 0);
-}
-bool DFA::SearchFFT(SearchParams* params) {
-  return InlinedSearchLoop(params, 0, 0, 1);
-}
-bool DFA::SearchFTF(SearchParams* params) {
-  return InlinedSearchLoop(params, 0, 1, 0);
-}
-bool DFA::SearchFTT(SearchParams* params) {
-  return InlinedSearchLoop(params, 0, 1, 1);
-}
-bool DFA::SearchTFF(SearchParams* params) {
-  return InlinedSearchLoop(params, 1, 0, 0);
-}
-bool DFA::SearchTFT(SearchParams* params) {
-  return InlinedSearchLoop(params, 1, 0, 1);
-}
-bool DFA::SearchTTF(SearchParams* params) {
-  return InlinedSearchLoop(params, 1, 1, 0);
-}
-bool DFA::SearchTTT(SearchParams* params) {
-  return InlinedSearchLoop(params, 1, 1, 1);
-}
-
-// For debugging, calls the general code directly.
-bool DFA::SlowSearchLoop(SearchParams* params) {
-  return InlinedSearchLoop(params,
-                           params->firstbyte >= 0,
-                           params->want_earliest_match,
-                           params->run_forward);
-}
-
-// For performance, calls the appropriate specialized version
-// of InlinedSearchLoop.
-bool DFA::FastSearchLoop(SearchParams* params) {
-  // Because the methods are private, the Searches array
-  // cannot be declared at top level.
-  static bool (DFA::*Searches[])(SearchParams*) = {
-    &DFA::SearchFFF,
-    &DFA::SearchFFT,
-    &DFA::SearchFTF,
-    &DFA::SearchFTT,
-    &DFA::SearchTFF,
-    &DFA::SearchTFT,
-    &DFA::SearchTTF,
-    &DFA::SearchTTT,
-  };
-
-  bool have_firstbyte = (params->firstbyte >= 0);
-  int index = 4 * have_firstbyte +
-              2 * params->want_earliest_match +
-              1 * params->run_forward;
-  return (this->*Searches[index])(params);
-}
-
-
-// The discussion of DFA execution above ignored the question of how
-// to determine the initial state for the search loop.  There are two
-// factors that influence the choice of start state.
-//
-// The first factor is whether the search is anchored or not.
-// The regexp program (Prog*) itself has
-// two different entry points: one for anchored searches and one for
-// unanchored searches.  (The unanchored version starts with a leading ".*?"
-// and then jumps to the anchored one.)
-//
-// The second factor is where text appears in the larger context, which
-// determines which empty-string operators can be matched at the beginning
-// of execution.  If text is at the very beginning of context, \A and ^ match.
-// Otherwise if text is at the beginning of a line, then ^ matches.
-// Otherwise it matters whether the character before text is a word character
-// or a non-word character.
-//
-// The two cases (unanchored vs not) and four cases (empty-string flags)
-// combine to make the eight cases recorded in the DFA's begin_text_[2],
-// begin_line_[2], after_wordchar_[2], and after_nonwordchar_[2] cached
-// StartInfos.  The start state for each is filled in the first time it
-// is used for an actual search.
-
-// Examines text, context, and anchored to determine the right start
-// state for the DFA search loop.  Fills in params and returns true on success.
-// Returns false on failure.
-bool DFA::AnalyzeSearch(SearchParams* params) {
-  const StringPiece& text = params->text;
-  const StringPiece& context = params->context;
-
-  // Sanity check: make sure that text lies within context.
-  if (text.begin() < context.begin() || text.end() > context.end()) {
-    LOG(DFATAL) << "Text is not inside context.";
-    params->start = DeadState;
-    return true;
-  }
-
-  // Determine correct search type.
-  int start;
-  uint flags;
-  if (params->run_forward) {
-    if (text.begin() == context.begin()) {
-      start = kStartBeginText;
-      flags = kEmptyBeginText|kEmptyBeginLine;
-    } else if (text.begin()[-1] == '\n') {
-      start = kStartBeginLine;
-      flags = kEmptyBeginLine;
-    } else if (Prog::IsWordChar(text.begin()[-1] & 0xFF)) {
-      start = kStartAfterWordChar;
-      flags = kFlagLastWord;
-    } else {
-      start = kStartAfterNonWordChar;
-      flags = 0;
-    }
-  } else {
-    if (text.end() == context.end()) {
-      start = kStartBeginText;
-      flags = kEmptyBeginText|kEmptyBeginLine;
-    } else if (text.end()[0] == '\n') {
-      start = kStartBeginLine;
-      flags = kEmptyBeginLine;
-    } else if (Prog::IsWordChar(text.end()[0] & 0xFF)) {
-      start = kStartAfterWordChar;
-      flags = kFlagLastWord;
-    } else {
-      start = kStartAfterNonWordChar;
-      flags = 0;
-    }
-  }
-  if (params->anchored || prog_->anchor_start())
-    start |= kStartAnchored;
-  StartInfo* info = &start_[start];
-
-  // Try once without cache_lock for writing.
-  // Try again after resetting the cache
-  // (ResetCache will relock cache_lock for writing).
-  if (!AnalyzeSearchHelper(params, info, flags)) {
-    ResetCache(params->cache_lock);
-    if (!AnalyzeSearchHelper(params, info, flags)) {
-      LOG(DFATAL) << "Failed to analyze start state.";
-      params->failed = true;
-      return false;
-    }
-  }
-
-  if (DebugDFA) {
-    int fb;
-    ATOMIC_LOAD_RELAXED(fb, &info->firstbyte);
-    fprintf(stderr, "anchored=%d fwd=%d flags=%#x state=%s firstbyte=%d\n",
-            params->anchored, params->run_forward, flags,
-            DumpState(info->start).c_str(), fb);
-  }
-
-  params->start = info->start;
-  ATOMIC_LOAD_ACQUIRE(params->firstbyte, &info->firstbyte);
-
-  return true;
-}
-
-// Fills in info if needed.  Returns true on success, false on failure.
-bool DFA::AnalyzeSearchHelper(SearchParams* params, StartInfo* info,
-                              uint flags) {
-  // Quick check.
-  int fb;
-  ATOMIC_LOAD_ACQUIRE(fb, &info->firstbyte);
-  if (fb != kFbUnknown)
-    return true;
-
-  MutexLock l(&mutex_);
-  if (info->firstbyte != kFbUnknown)
-    return true;
-
-  q0_->clear();
-  AddToQueue(q0_,
-             params->anchored ? prog_->start() : prog_->start_unanchored(),
-             flags);
-  info->start = WorkqToCachedState(q0_, flags);
-  if (info->start == NULL)
-    return false;
-
-  if (info->start == DeadState) {
-    // Synchronize with "quick check" above.
-    ATOMIC_STORE_RELEASE(&info->firstbyte, kFbNone);
-    return true;
-  }
-
-  if (info->start == FullMatchState) {
-    // Synchronize with "quick check" above.
-    ATOMIC_STORE_RELEASE(&info->firstbyte, kFbNone);    // will be ignored
-    return true;
-  }
-
-  // Compute info->firstbyte by running state on all
-  // possible byte values, looking for a single one that
-  // leads to a different state.
-  int firstbyte = kFbNone;
-  for (int i = 0; i < 256; i++) {
-    State* s = RunStateOnByte(info->start, i);
-    if (s == NULL) {
-      // Synchronize with "quick check" above.
-      ATOMIC_STORE_RELEASE(&info->firstbyte, firstbyte);
-      return false;
-    }
-    if (s == info->start)
-      continue;
-    // Goes to new state...
-    if (firstbyte == kFbNone) {
-      firstbyte = i;        // ... first one
-    } else {
-      firstbyte = kFbMany;  // ... too many
-      break;
-    }
-  }
-  // Synchronize with "quick check" above.
-  ATOMIC_STORE_RELEASE(&info->firstbyte, firstbyte);
-  return true;
-}
-
-// The actual DFA search: calls AnalyzeSearch and then FastSearchLoop.
-bool DFA::Search(const StringPiece& text,
-                 const StringPiece& context,
-                 bool anchored,
-                 bool want_earliest_match,
-                 bool run_forward,
-                 bool* failed,
-                 const char** epp,
-                 vector<int>* matches) {
-  *epp = NULL;
-  if (!ok()) {
-    *failed = true;
-    return false;
-  }
-  *failed = false;
-
-  if (DebugDFA) {
-    fprintf(stderr, "\nprogram:\n%s\n", prog_->DumpUnanchored().c_str());
-    fprintf(stderr, "text %s anchored=%d earliest=%d fwd=%d kind %d\n",
-            text.as_string().c_str(), anchored, want_earliest_match,
-            run_forward, kind_);
-  }
-
-  RWLocker l(&cache_mutex_);
-  SearchParams params(text, context, &l);
-  params.anchored = anchored;
-  params.want_earliest_match = want_earliest_match;
-  params.run_forward = run_forward;
-  params.matches = matches;
-
-  if (!AnalyzeSearch(&params)) {
-    *failed = true;
-    return false;
-  }
-  if (params.start == DeadState)
-    return false;
-  if (params.start == FullMatchState) {
-    if (run_forward == want_earliest_match)
-      *epp = text.begin();
-    else
-      *epp = text.end();
-    return true;
-  }
-  if (DebugDFA)
-    fprintf(stderr, "start %s\n", DumpState(params.start).c_str());
-  bool ret = FastSearchLoop(&params);
-  if (params.failed) {
-    *failed = true;
-    return false;
-  }
-  *epp = params.ep;
-  return ret;
-}
-
-// Deletes dfa.
-//
-// This is a separate function so that
-// prog.h can be used without moving the definition of
-// class DFA out of this file.  If you set
-//   prog->dfa_ = dfa;
-// then you also have to set
-//   prog->delete_dfa_ = DeleteDFA;
-// so that ~Prog can delete the dfa.
-static void DeleteDFA(DFA* dfa) {
-  delete dfa;
-}
-
-DFA* Prog::GetDFA(MatchKind kind) {
-  DFA*volatile* pdfa;
-  if (kind == kFirstMatch || kind == kManyMatch) {
-    pdfa = &dfa_first_;
-  } else {
-    kind = kLongestMatch;
-    pdfa = &dfa_longest_;
-  }
-
-  // Quick check.
-  DFA *dfa;
-  ATOMIC_LOAD_ACQUIRE(dfa, pdfa);
-  if (dfa != NULL)
-    return dfa;
-
-  MutexLock l(&dfa_mutex_);
-  dfa = *pdfa;
-  if (dfa != NULL)
-    return dfa;
-
-  // For a forward DFA, half the memory goes to each DFA.
-  // For a reverse DFA, all the memory goes to the
-  // "longest match" DFA, because RE2 never does reverse
-  // "first match" searches.
-  int64 m = dfa_mem_/2;
-  if (reversed_) {
-    if (kind == kLongestMatch || kind == kManyMatch)
-      m = dfa_mem_;
-    else
-      m = 0;
-  }
-  dfa = new DFA(this, kind, m);
-  delete_dfa_ = DeleteDFA;
-
-  // Synchronize with "quick check" above.
-  ATOMIC_STORE_RELEASE(pdfa, dfa);
-
-  return dfa;
-}
-
-
-// Executes the regexp program to search in text,
-// which itself is inside the larger context.  (As a convenience,
-// passing a NULL context is equivalent to passing text.)
-// Returns true if a match is found, false if not.
-// If a match is found, fills in match0->end() to point at the end of the match
-// and sets match0->begin() to text.begin(), since the DFA can't track
-// where the match actually began.
-//
-// This is the only external interface (class DFA only exists in this file).
-//
-bool Prog::SearchDFA(const StringPiece& text, const StringPiece& const_context,
-                     Anchor anchor, MatchKind kind,
-                     StringPiece* match0, bool* failed, vector<int>* matches) {
-  *failed = false;
-
-  StringPiece context = const_context;
-  if (context.begin() == NULL)
-    context = text;
-  bool carat = anchor_start();
-  bool dollar = anchor_end();
-  if (reversed_) {
-    bool t = carat;
-    carat = dollar;
-    dollar = t;
-  }
-  if (carat && context.begin() != text.begin())
-    return false;
-  if (dollar && context.end() != text.end())
-    return false;
-
-  // Handle full match by running an anchored longest match
-  // and then checking if it covers all of text.
-  bool anchored = anchor == kAnchored || anchor_start() || kind == kFullMatch;
-  bool endmatch = false;
-  if (kind == kManyMatch) {
-    endmatch = true;
-  } else if (kind == kFullMatch || anchor_end()) {
-    endmatch = true;
-    kind = kLongestMatch;
-  }
-
-  // If the caller doesn't care where the match is (just whether one exists),
-  // then we can stop at the very first match we find, the so-called
-  // "shortest match".
-  bool want_shortest_match = false;
-  if (match0 == NULL && !endmatch) {
-    want_shortest_match = true;
-    kind = kLongestMatch;
-  }
-
-  DFA* dfa = GetDFA(kind);
-  const char* ep;
-  bool matched = dfa->Search(text, context, anchored,
-                             want_shortest_match, !reversed_,
-                             failed, &ep, matches);
-  if (*failed)
-    return false;
-  if (!matched)
-    return false;
-  if (endmatch && ep != (reversed_ ? text.begin() : text.end()))
-    return false;
-
-  // If caller cares, record the boundary of the match.
-  // We only know where it ends, so use the boundary of text
-  // as the beginning.
-  if (match0) {
-    if (reversed_)
-      match0->set(ep, static_cast<int>(text.end() - ep));
-    else
-      match0->set(text.begin(), static_cast<int>(ep - text.begin()));
-  }
-  return true;
-}
-
-// Build out all states in DFA.  Returns number of states.
-int DFA::BuildAllStates() {
-  if (!ok())
-    return 0;
-
-  // Pick out start state for unanchored search
-  // at beginning of text.
-  RWLocker l(&cache_mutex_);
-  SearchParams params(NULL, NULL, &l);
-  params.anchored = false;
-  if (!AnalyzeSearch(&params) || params.start <= SpecialStateMax)
-    return 0;
-
-  // Add start state to work queue.
-  StateSet queued;
-  vector<State*> q;
-  queued.insert(params.start);
-  q.push_back(params.start);
-
-  // Flood to expand every state.
-  for (size_t i = 0; i < q.size(); i++) {
-    State* s = q[i];
-    for (int c = 0; c < 257; c++) {
-      State* ns = RunStateOnByteUnlocked(s, c);
-      if (ns > SpecialStateMax && queued.find(ns) == queued.end()) {
-        queued.insert(ns);
-        q.push_back(ns);
-      }
-    }
-  }
-
-  return static_cast<int>(q.size());
-}
-
-// Build out all states in DFA for kind.  Returns number of states.
-int Prog::BuildEntireDFA(MatchKind kind) {
-  //LOG(ERROR) << "BuildEntireDFA is only for testing.";
-  return GetDFA(kind)->BuildAllStates();
-}
-
-// Computes min and max for matching string.
-// Won't return strings bigger than maxlen.
-bool DFA::PossibleMatchRange(string* min, string* max, int maxlen) {
-  if (!ok())
-    return false;
-
-  // NOTE: if future users of PossibleMatchRange want more precision when
-  // presented with infinitely repeated elements, consider making this a
-  // parameter to PossibleMatchRange.
-  static int kMaxEltRepetitions = 0;
-
-  // Keep track of the number of times we've visited states previously. We only
-  // revisit a given state if it's part of a repeated group, so if the value
-  // portion of the map tuple exceeds kMaxEltRepetitions we bail out and set
-  // |*max| to |PrefixSuccessor(*max)|.
-  //
-  // Also note that previously_visited_states[UnseenStatePtr] will, in the STL
-  // tradition, implicitly insert a '0' value at first use. We take advantage
-  // of that property below.
-  map<State*, int> previously_visited_states;
-
-  // Pick out start state for anchored search at beginning of text.
-  RWLocker l(&cache_mutex_);
-  SearchParams params(NULL, NULL, &l);
-  params.anchored = true;
-  if (!AnalyzeSearch(&params))
-    return false;
-  if (params.start == DeadState) {  // No matching strings
-    *min = "";
-    *max = "";
-    return true;
-  }
-  if (params.start == FullMatchState)  // Every string matches: no max
-    return false;
-
-  // The DFA is essentially a big graph rooted at params.start,
-  // and paths in the graph correspond to accepted strings.
-  // Each node in the graph has potentially 256+1 arrows
-  // coming out, one for each byte plus the magic end of
-  // text character kByteEndText.
-
-  // To find the smallest possible prefix of an accepted
-  // string, we just walk the graph preferring to follow
-  // arrows with the lowest bytes possible.  To find the
-  // largest possible prefix, we follow the largest bytes
-  // possible.
-
-  // The test for whether there is an arrow from s on byte j is
-  //    ns = RunStateOnByteUnlocked(s, j);
-  //    if (ns == NULL)
-  //      return false;
-  //    if (ns != DeadState && ns->ninst > 0)
-  // The RunStateOnByteUnlocked call asks the DFA to build out the graph.
-  // It returns NULL only if the DFA has run out of memory,
-  // in which case we can't be sure of anything.
-  // The second check sees whether there was graph built
-  // and whether it is interesting graph.  Nodes might have
-  // ns->ninst == 0 if they exist only to represent the fact
-  // that a match was found on the previous byte.
-
-  // Build minimum prefix.
-  State* s = params.start;
-  min->clear();
-  MutexLock lock(&mutex_);
-  for (int i = 0; i < maxlen; i++) {
-    if (previously_visited_states[s] > kMaxEltRepetitions) {
-      VLOG(2) << "Hit kMaxEltRepetitions=" << kMaxEltRepetitions
-        << " for state s=" << s << " and min=" << CEscape(*min);
-      break;
-    }
-    previously_visited_states[s]++;
-
-    // Stop if min is a match.
-    State* ns = RunStateOnByte(s, kByteEndText);
-    if (ns == NULL)  // DFA out of memory
-      return false;
-    if (ns != DeadState && (ns == FullMatchState || ns->IsMatch()))
-      break;
-
-    // Try to extend the string with low bytes.
-    bool extended = false;
-    for (int j = 0; j < 256; j++) {
-      ns = RunStateOnByte(s, j);
-      if (ns == NULL)  // DFA out of memory
-        return false;
-      if (ns == FullMatchState ||
-          (ns > SpecialStateMax && ns->ninst_ > 0)) {
-        extended = true;
-        min->append(1, static_cast<char>(j));
-        s = ns;
-        break;
-      }
-    }
-    if (!extended)
-      break;
-  }
-
-  // Build maximum prefix.
-  previously_visited_states.clear();
-  s = params.start;
-  max->clear();
-  for (int i = 0; i < maxlen; i++) {
-    if (previously_visited_states[s] > kMaxEltRepetitions) {
-      VLOG(2) << "Hit kMaxEltRepetitions=" << kMaxEltRepetitions
-        << " for state s=" << s << " and max=" << CEscape(*max);
-      break;
-    }
-    previously_visited_states[s] += 1;
-
-    // Try to extend the string with high bytes.
-    bool extended = false;
-    for (int j = 255; j >= 0; j--) {
-      State* ns = RunStateOnByte(s, j);
-      if (ns == NULL)
-        return false;
-      if (ns == FullMatchState ||
-          (ns > SpecialStateMax && ns->ninst_ > 0)) {
-        extended = true;
-        max->append(1, static_cast<char>(j));
-        s = ns;
-        break;
-      }
-    }
-    if (!extended) {
-      // Done, no need for PrefixSuccessor.
-      return true;
-    }
-  }
-
-  // Stopped while still adding to *max - round aaaaaaaaaa... to aaaa...b
-  *max = PrefixSuccessor(*max);
-
-  // If there are no bytes left, we have no way to say "there is no maximum
-  // string".  We could make the interface more complicated and be able to
-  // return "there is no maximum but here is a minimum", but that seems like
-  // overkill -- the most common no-max case is all possible strings, so not
-  // telling the caller that the empty string is the minimum match isn't a
-  // great loss.
-  if (max->empty())
-    return false;
-
-  return true;
-}
-
-// PossibleMatchRange for a Prog.
-bool Prog::PossibleMatchRange(string* min, string* max, int maxlen) {
-  DFA* dfa = NULL;
-  {
-    MutexLock l(&dfa_mutex_);
-    // Have to use dfa_longest_ to get all strings for full matches.
-    // For example, (a|aa) never matches aa in first-match mode.
-    dfa = dfa_longest_;
-    if (dfa == NULL) {
-      dfa = new DFA(this, Prog::kLongestMatch, dfa_mem_/2);
-      ATOMIC_STORE_RELEASE(&dfa_longest_, dfa);
-      delete_dfa_ = DeleteDFA;
-    }
-  }
-  return dfa->PossibleMatchRange(min, max, maxlen);
-}
-
-}  // namespace re2