Include RE2 library

third_party/re2/re2/onepass.cc

Index: third_party/re2/re2/onepass.cc
diff --git a/third_party/re2/re2/onepass.cc b/third_party/re2/re2/onepass.cc
new file mode 100644
index 0000000000000000000000000000000000000000..1c4998828b500a86ad7eceac27a1cd94d3e90de4
--- /dev/null
+++ b/third_party/re2/re2/onepass.cc
@@ -0,0 +1,614 @@
+// 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.
+
+// Tested by search_test.cc.
+//
+// Prog::SearchOnePass is an efficient implementation of
+// regular expression search with submatch tracking for
+// what I call "one-pass regular expressions".  (An alternate
+// name might be "backtracking-free regular expressions".)
+//
+// One-pass regular expressions have the property that
+// at each input byte during an anchored match, there may be
+// multiple alternatives but only one can proceed for any
+// given input byte.
+//
+// For example, the regexp /x*yx*/ is one-pass: you read
+// x's until a y, then you read the y, then you keep reading x's.
+// At no point do you have to guess what to do or back up
+// and try a different guess.
+//
+// On the other hand, /x*x/ is not one-pass: when you're
+// looking at an input "x", it's not clear whether you should
+// use it to extend the x* or as the final x.
+//
+// More examples: /([^ ]*) (.*)/ is one-pass; /(.*) (.*)/ is not.
+// /(\d+)-(\d+)/ is one-pass; /(\d+).(\d+)/ is not.
+//
+// A simple intuition for identifying one-pass regular expressions
+// is that it's always immediately obvious when a repetition ends.
+// It must also be immediately obvious which branch of an | to take:
+//
+// /x(y|z)/ is one-pass, but /(xy|xz)/ is not.
+//
+// The NFA-based search in nfa.cc does some bookkeeping to
+// avoid the need for backtracking and its associated exponential blowup.
+// But if we have a one-pass regular expression, there is no
+// possibility of backtracking, so there is no need for the
+// extra bookkeeping.  Hence, this code.
+//
+// On a one-pass regular expression, the NFA code in nfa.cc
+// runs at about 1/20 of the backtracking-based PCRE speed.
+// In contrast, the code in this file runs at about the same
+// speed as PCRE.
+//
+// One-pass regular expressions get used a lot when RE is
+// used for parsing simple strings, so it pays off to
+// notice them and handle them efficiently.
+//
+// See also Anne Brüggemann-Klein and Derick Wood,
+// "One-unambiguous regular languages", Information and Computation 142(2).
+
+#include <string.h>
+#include <map>
+#include "util/util.h"
+#include "util/arena.h"
+#include "util/sparse_set.h"
+#include "re2/prog.h"
+#include "re2/stringpiece.h"
+
+namespace re2 {
+
+static const int Debug = 0;
+
+// The key insight behind this implementation is that the
+// non-determinism in an NFA for a one-pass regular expression
+// is contained.  To explain what that means, first a
+// refresher about what regular expression programs look like
+// and how the usual NFA execution runs.
+//
+// In a regular expression program, only the kInstByteRange
+// instruction processes an input byte c and moves on to the
+// next byte in the string (it does so if c is in the given range).
+// The kInstByteRange instructions correspond to literal characters
+// and character classes in the regular expression.
+//
+// The kInstAlt instructions are used as wiring to connect the
+// kInstByteRange instructions together in interesting ways when
+// implementing | + and *.
+// The kInstAlt instruction forks execution, like a goto that
+// jumps to ip->out() and ip->out1() in parallel.  Each of the
+// resulting computation paths is called a thread.
+//
+// The other instructions -- kInstEmptyWidth, kInstMatch, kInstCapture --
+// are interesting in their own right but like kInstAlt they don't
+// advance the input pointer.  Only kInstByteRange does.
+//
+// The automaton execution in nfa.cc runs all the possible
+// threads of execution in lock-step over the input.  To process
+// a particular byte, each thread gets run until it either dies
+// or finds a kInstByteRange instruction matching the byte.
+// If the latter happens, the thread stops just past the
+// kInstByteRange instruction (at ip->out()) and waits for
+// the other threads to finish processing the input byte.
+// Then, once all the threads have processed that input byte,
+// the whole process repeats.  The kInstAlt state instruction
+// might create new threads during input processing, but no
+// matter what, all the threads stop after a kInstByteRange
+// and wait for the other threads to "catch up".
+// Running in lock step like this ensures that the NFA reads
+// the input string only once.
+//
+// Each thread maintains its own set of capture registers
+// (the string positions at which it executed the kInstCapture
+// instructions corresponding to capturing parentheses in the
+// regular expression).  Repeated copying of the capture registers
+// is the main performance bottleneck in the NFA implementation.
+//
+// A regular expression program is "one-pass" if, no matter what
+// the input string, there is only one thread that makes it
+// past a kInstByteRange instruction at each input byte.  This means
+// that there is in some sense only one active thread throughout
+// the execution.  Other threads might be created during the
+// processing of an input byte, but they are ephemeral: only one
+// thread is left to start processing the next input byte.
+// This is what I meant above when I said the non-determinism
+// was "contained".
+//
+// To execute a one-pass regular expression program, we can build
+// a DFA (no non-determinism) that has at most as many states as
+// the NFA (compare this to the possibly exponential number of states
+// in the general case).  Each state records, for each possible
+// input byte, the next state along with the conditions required
+// before entering that state -- empty-width flags that must be true
+// and capture operations that must be performed.  It also records
+// whether a set of conditions required to finish a match at that
+// point in the input rather than process the next byte.
+
+// A state in the one-pass NFA (aka DFA) - just an array of actions.
+struct OneState;
+
+// A state in the one-pass NFA - just an array of actions indexed
+// by the bytemap_[] of the next input byte.  (The bytemap
+// maps next input bytes into equivalence classes, to reduce
+// the memory footprint.)
+struct OneState {
+  uint32 matchcond;   // conditions to match right now.
+  uint32 action[1];
+};
+
+// The uint32 conditions in the action are a combination of
+// condition and capture bits and the next state.  The bottom 16 bits
+// are the condition and capture bits, and the top 16 are the index of
+// the next state.
+//
+// Bits 0-5 are the empty-width flags from prog.h.
+// Bit 6 is kMatchWins, which means the match takes
+// priority over moving to next in a first-match search.
+// The remaining bits mark capture registers that should
+// be set to the current input position.  The capture bits
+// start at index 2, since the search loop can take care of
+// cap[0], cap[1] (the overall match position).
+// That means we can handle up to 5 capturing parens: $1 through $4, plus $0.
+// No input position can satisfy both kEmptyWordBoundary
+// and kEmptyNonWordBoundary, so we can use that as a sentinel
+// instead of needing an extra bit.
+
+static const int    kIndexShift    = 16;  // number of bits below index
+static const int    kEmptyShift   = 6;  // number of empty flags in prog.h
+static const int    kRealCapShift = kEmptyShift + 1;
+static const int    kRealMaxCap   = (kIndexShift - kRealCapShift) / 2 * 2;
+
+// Parameters used to skip over cap[0], cap[1].
+static const int    kCapShift     = kRealCapShift - 2;
+static const int    kMaxCap       = kRealMaxCap + 2;
+
+static const uint32 kMatchWins    = 1 << kEmptyShift;
+static const uint32 kCapMask      = ((1 << kRealMaxCap) - 1) << kRealCapShift;
+
+static const uint32 kImpossible   = kEmptyWordBoundary | kEmptyNonWordBoundary;
+
+// Check, at compile time, that prog.h agrees with math above.
+// This function is never called.
+void OnePass_Checks() {
+  COMPILE_ASSERT((1<<kEmptyShift)-1 == kEmptyAllFlags,
+                 kEmptyShift_disagrees_with_kEmptyAllFlags);
+  // kMaxCap counts pointers, kMaxOnePassCapture counts pairs.
+  COMPILE_ASSERT(kMaxCap == Prog::kMaxOnePassCapture*2,
+                 kMaxCap_disagrees_with_kMaxOnePassCapture);
+}
+
+static bool Satisfy(uint32 cond, const StringPiece& context, const char* p) {
+  uint32 satisfied = Prog::EmptyFlags(context, p);
+  if (cond & kEmptyAllFlags & ~satisfied)
+    return false;
+  return true;
+}
+
+// Apply the capture bits in cond, saving p to the appropriate
+// locations in cap[].
+static void ApplyCaptures(uint32 cond, const char* p,
+                          const char** cap, int ncap) {
+  for (int i = 2; i < ncap; i++)
+    if (cond & (1 << kCapShift << i))
+      cap[i] = p;
+}
+
+// Compute a node pointer.
+// Basically (OneState*)(nodes + statesize*nodeindex)
+// but the version with the C++ casts overflows 80 characters (and is ugly).
+static inline OneState* IndexToNode(volatile uint8* nodes, int statesize,
+                                    int nodeindex) {
+  return reinterpret_cast<OneState*>(
+    const_cast<uint8*>(nodes + statesize*nodeindex));
+}
+
+bool Prog::SearchOnePass(const StringPiece& text,
+                         const StringPiece& const_context,
+                         Anchor anchor, MatchKind kind,
+                         StringPiece* match, int nmatch) {
+  if (anchor != kAnchored && kind != kFullMatch) {
+    LOG(DFATAL) << "Cannot use SearchOnePass for unanchored matches.";
+    return false;
+  }
+
+  // Make sure we have at least cap[1],
+  // because we use it to tell if we matched.
+  int ncap = 2*nmatch;
+  if (ncap < 2)
+    ncap = 2;
+
+  const char* cap[kMaxCap];
+  for (int i = 0; i < ncap; i++)
+    cap[i] = NULL;
+
+  const char* matchcap[kMaxCap];
+  for (int i = 0; i < ncap; i++)
+    matchcap[i] = NULL;
+
+  StringPiece context = const_context;
+  if (context.begin() == NULL)
+    context = text;
+  if (anchor_start() && context.begin() != text.begin())
+    return false;
+  if (anchor_end() && context.end() != text.end())
+    return false;
+  if (anchor_end())
+    kind = kFullMatch;
+
+  // State and act are marked volatile to
+  // keep the compiler from re-ordering the
+  // memory accesses walking over the NFA.
+  // This is worth about 5%.
+  volatile OneState* state = onepass_start_;
+  volatile uint8* nodes = onepass_nodes_;
+  volatile uint32 statesize = onepass_statesize_;
+  uint8* bytemap = bytemap_;
+  const char* bp = text.begin();
+  const char* ep = text.end();
+  const char* p;
+  bool matched = false;
+  matchcap[0] = bp;
+  cap[0] = bp;
+  uint32 nextmatchcond = state->matchcond;
+  for (p = bp; p < ep; p++) {
+    int c = bytemap[*p & 0xFF];
+    uint32 matchcond = nextmatchcond;
+    uint32 cond = state->action[c];
+
+    // Determine whether we can reach act->next.
+    // If so, advance state and nextmatchcond.
+    if ((cond & kEmptyAllFlags) == 0 || Satisfy(cond, context, p)) {
+      uint32 nextindex = cond >> kIndexShift;
+      state = IndexToNode(nodes, statesize, nextindex);
+      nextmatchcond = state->matchcond;
+    } else {
+      state = NULL;
+      nextmatchcond = kImpossible;
+    }
+
+    // This code section is carefully tuned.
+    // The goto sequence is about 10% faster than the
+    // obvious rewrite as a large if statement in the
+    // ASCIIMatchRE2 and DotMatchRE2 benchmarks.
+
+    // Saving the match capture registers is expensive.
+    // Is this intermediate match worth thinking about?
+
+    // Not if we want a full match.
+    if (kind == kFullMatch)
+      goto skipmatch;
+
+    // Not if it's impossible.
+    if (matchcond == kImpossible)
+      goto skipmatch;
+
+    // Not if the possible match is beaten by the certain
+    // match at the next byte.  When this test is useless
+    // (e.g., HTTPPartialMatchRE2) it slows the loop by
+    // about 10%, but when it avoids work (e.g., DotMatchRE2),
+    // it cuts the loop execution by about 45%.
+    if ((cond & kMatchWins) == 0 && (nextmatchcond & kEmptyAllFlags) == 0)
+      goto skipmatch;
+
+    // Finally, the match conditions must be satisfied.
+    if ((matchcond & kEmptyAllFlags) == 0 || Satisfy(matchcond, context, p)) {
+      for (int i = 2; i < 2*nmatch; i++)
+        matchcap[i] = cap[i];
+      if (nmatch > 1 && (matchcond & kCapMask))
+        ApplyCaptures(matchcond, p, matchcap, ncap);
+      matchcap[1] = p;
+      matched = true;
+
+      // If we're in longest match mode, we have to keep
+      // going and see if we find a longer match.
+      // In first match mode, we can stop if the match
+      // takes priority over the next state for this input byte.
+      // That bit is per-input byte and thus in cond, not matchcond.
+      if (kind == kFirstMatch && (cond & kMatchWins))
+        goto done;
+    }
+
+  skipmatch:
+    if (state == NULL)
+      goto done;
+    if ((cond & kCapMask) && nmatch > 1)
+      ApplyCaptures(cond, p, cap, ncap);
+  }
+
+  // Look for match at end of input.
+  {
+    uint32 matchcond = state->matchcond;
+    if (matchcond != kImpossible &&
+        ((matchcond & kEmptyAllFlags) == 0 || Satisfy(matchcond, context, p))) {
+      if (nmatch > 1 && (matchcond & kCapMask))
+        ApplyCaptures(matchcond, p, cap, ncap);
+      for (int i = 2; i < ncap; i++)
+        matchcap[i] = cap[i];
+      matchcap[1] = p;
+      matched = true;
+    }
+  }
+
+done:
+  if (!matched)
+    return false;
+  for (int i = 0; i < nmatch; i++)
+    match[i].set(matchcap[2*i], matchcap[2*i+1] - matchcap[2*i]);
+  return true;
+}
+
+
+// Analysis to determine whether a given regexp program is one-pass.
+
+// If ip is not on workq, adds ip to work queue and returns true.
+// If ip is already on work queue, does nothing and returns false.
+// If ip is NULL, does nothing and returns true (pretends to add it).
+typedef SparseSet Instq;
+static bool AddQ(Instq *q, int id) {
+  if (id == 0)
+    return true;
+  if (q->contains(id))
+    return false;
+  q->insert(id);
+  return true;
+}
+
+struct InstCond {
+  int id;
+  uint32 cond;
+};
+
+// Returns whether this is a one-pass program; that is,
+// returns whether it is safe to use SearchOnePass on this program.
+// These conditions must be true for any instruction ip:
+//
+//   (1) for any other Inst nip, there is at most one input-free
+//       path from ip to nip.
+//   (2) there is at most one kInstByte instruction reachable from
+//       ip that matches any particular byte c.
+//   (3) there is at most one input-free path from ip to a kInstMatch
+//       instruction.
+//
+// This is actually just a conservative approximation: it might
+// return false when the answer is true, when kInstEmptyWidth
+// instructions are involved.
+// Constructs and saves corresponding one-pass NFA on success.
+bool Prog::IsOnePass() {
+  if (did_onepass_)
+    return onepass_start_ != NULL;
+  did_onepass_ = true;
+
+  if (start() == 0)  // no match
+    return false;
+
+  // Steal memory for the one-pass NFA from the overall DFA budget.
+  // Willing to use at most 1/4 of the DFA budget (heuristic).
+  // Limit max node count to 65000 as a conservative estimate to
+  // avoid overflowing 16-bit node index in encoding.
+  int maxnodes = 2 + byte_inst_count_;
+  int statesize = sizeof(OneState) + (bytemap_range_-1)*sizeof(uint32);
+  if (maxnodes >= 65000 || dfa_mem_ / 4 / statesize < maxnodes)
+    return false;
+
+  // Flood the graph starting at the start state, and check
+  // that in each reachable state, each possible byte leads
+  // to a unique next state.
+  int size = this->size();
+  InstCond *stack = new InstCond[size];
+
+  int* nodebyid = new int[size];  // indexed by ip
+  memset(nodebyid, 0xFF, size*sizeof nodebyid[0]);
+
+  uint8* nodes = new uint8[maxnodes*statesize];
+  uint8* nodep = nodes;
+
+  Instq tovisit(size), workq(size);
+  AddQ(&tovisit, start());
+  nodebyid[start()] = 0;
+  nodep += statesize;
+  int nalloc = 1;
+  for (Instq::iterator it = tovisit.begin(); it != tovisit.end(); ++it) {
+    int id = *it;
+    int nodeindex = nodebyid[id];
+    OneState* node = IndexToNode(nodes, statesize, nodeindex);
+
+    // Flood graph using manual stack, filling in actions as found.
+    // Default is none.
+    for (int b = 0; b < bytemap_range_; b++)
+      node->action[b] = kImpossible;
+    node->matchcond = kImpossible;
+
+    workq.clear();
+    bool matched = false;
+    int nstack = 0;
+    stack[nstack].id = id;
+    stack[nstack++].cond = 0;
+    while (nstack > 0) {
+      int id = stack[--nstack].id;
+      Prog::Inst* ip = inst(id);
+      uint32 cond = stack[nstack].cond;
+      switch (ip->opcode()) {
+        case kInstAltMatch:
+          // TODO(rsc): Ignoring kInstAltMatch optimization.
+          // Should implement it in this engine, but it's subtle.
+          // Fall through.
+        case kInstAlt:
+          // If already on work queue, (1) is violated: bail out.
+          if (!AddQ(&workq, ip->out()) || !AddQ(&workq, ip->out1()))
+            goto fail;
+          stack[nstack].id = ip->out1();
+          stack[nstack++].cond = cond;
+          stack[nstack].id = ip->out();
+          stack[nstack++].cond = cond;
+          break;
+
+        case kInstByteRange: {
+          int nextindex = nodebyid[ip->out()];
+          if (nextindex == -1) {
+            if (nalloc >= maxnodes) {
+              if (Debug)
+                LOG(ERROR)
+                  << StringPrintf("Not OnePass: hit node limit %d > %d",
+                                  nalloc, maxnodes);
+              goto fail;
+            }
+            nextindex = nalloc;
+            nodep += statesize;
+            nodebyid[ip->out()] = nextindex;
+            nalloc++;
+            AddQ(&tovisit, ip->out());
+          }
+          if (matched)
+            cond |= kMatchWins;
+          for (int c = ip->lo(); c <= ip->hi(); c++) {
+            int b = bytemap_[c];
+            c = unbytemap_[b];  // last c in byte class
+            uint32 act = node->action[b];
+            uint32 newact = (nextindex << kIndexShift) | cond;
+            if ((act & kImpossible) == kImpossible) {
+              node->action[b] = newact;
+            } else if (act != newact) {
+              if (Debug) {
+                LOG(ERROR)
+                  << StringPrintf("Not OnePass: conflict on byte "
+                                  "%#x at state %d",
+                                  c, *it);
+              }
+              goto fail;
+            }
+          }
+          if (ip->foldcase()) {
+            Rune lo = max<Rune>(ip->lo(), 'a') + 'A' - 'a';
+            Rune hi = min<Rune>(ip->hi(), 'z') + 'A' - 'a';
+            for (int c = lo; c <= hi; c++) {
+              int b = bytemap_[c];
+              c = unbytemap_[b];  // last c in class
+              uint32 act = node->action[b];
+              uint32 newact = (nextindex << kIndexShift) | cond;
+              if ((act & kImpossible) == kImpossible) {
+                node->action[b] = newact;
+              } else if (act != newact) {
+                if (Debug) {
+                  LOG(ERROR)
+                    << StringPrintf("Not OnePass: conflict on byte "
+                                    "%#x at state %d",
+                                    c, *it);
+                }
+                goto fail;
+              }
+            }
+          }
+          break;
+        }
+
+        case kInstCapture:
+          if (ip->cap() < kMaxCap)
+            cond |= (1 << kCapShift) << ip->cap();
+          goto QueueEmpty;
+
+        case kInstEmptyWidth:
+          cond |= ip->empty();
+          goto QueueEmpty;
+
+        case kInstNop:
+        QueueEmpty:
+          // kInstCapture and kInstNop always proceed to ip->out().
+          // kInstEmptyWidth only sometimes proceeds to ip->out(),
+          // but as a conservative approximation we assume it always does.
+          // We could be a little more precise by looking at what c
+          // is, but that seems like overkill.
+
+          // If already on work queue, (1) is violated: bail out.
+          if (!AddQ(&workq, ip->out())) {
+            if (Debug) {
+              LOG(ERROR) << StringPrintf("Not OnePass: multiple paths"
+                                         " %d -> %d\n",
+                                         *it, ip->out());
+            }
+            goto fail;
+          }
+          stack[nstack].id = ip->out();
+          stack[nstack++].cond = cond;
+          break;
+
+        case kInstMatch:
+          if (matched) {
+            // (3) is violated
+            if (Debug) {
+              LOG(ERROR) << StringPrintf("Not OnePass: multiple matches"
+                                         " from %d\n", *it);
+            }
+            goto fail;
+          }
+          matched = true;
+          node->matchcond = cond;
+          break;
+
+        case kInstFail:
+          break;
+      }
+    }
+  }
+
+  if (Debug) {  // For debugging, dump one-pass NFA to LOG(ERROR).
+    string dump = "prog dump:\n" + Dump() + "node dump\n";
+    map<int, int> idmap;
+    for (int i = 0; i < size; i++)
+      if (nodebyid[i] != -1)
+        idmap[nodebyid[i]] = i;
+
+    StringAppendF(&dump, "byte ranges:\n");
+    int i = 0;
+    for (int b = 0; b < bytemap_range_; b++) {
+      int lo = i;
+      while (bytemap_[i] == b)
+        i++;
+      StringAppendF(&dump, "\t%d: %#x-%#x\n", b, lo, i - 1);
+    }
+
+    for (Instq::iterator it = tovisit.begin(); it != tovisit.end(); ++it) {
+      int id = *it;
+      int nodeindex = nodebyid[id];
+      if (nodeindex == -1)
+      	continue;
+      OneState* node = IndexToNode(nodes, statesize, nodeindex);
+      string s;
+      StringAppendF(&dump, "node %d id=%d: matchcond=%#x\n",
+                    nodeindex, id, node->matchcond);
+      for (int i = 0; i < bytemap_range_; i++) {
+        if ((node->action[i] & kImpossible) == kImpossible)
+          continue;
+        StringAppendF(&dump, "  %d cond %#x -> %d id=%d\n",
+                      i, node->action[i] & 0xFFFF,
+                      node->action[i] >> kIndexShift,
+                      idmap[node->action[i] >> kIndexShift]);
+      }
+    }
+    LOG(ERROR) << dump;
+  }
+
+  // Overallocated earlier; cut down to actual size.
+  nodep = new uint8[nalloc*statesize];
+  memmove(nodep, nodes, nalloc*statesize);
+  delete[] nodes;
+  nodes = nodep;
+
+  onepass_start_ = IndexToNode(nodes, statesize, nodebyid[start()]);
+  onepass_nodes_ = nodes;
+  onepass_statesize_ = statesize;
+  dfa_mem_ -= nalloc*statesize;
+
+  delete[] stack;
+  delete[] nodebyid;
+  return true;
+
+fail:
+  delete[] stack;
+  delete[] nodebyid;
+  delete[] nodes;
+  return false;
+}
+
+}  // namespace re2