diff -r 000000000000 -r 6474c204b198 js/src/vm/MatchPairs.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/vm/MatchPairs.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,174 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_MatchPairs_h
+#define vm_MatchPairs_h
+
+#include "jsalloc.h"
+
+#include "ds/LifoAlloc.h"
+#include "js/Vector.h"
+
+/*
+ * RegExp match results are succinctly represented by pairs of integer
+ * indices delimiting (start, limit] segments of the input string.
+ *
+ * The pair count for a given RegExp match is the capturing parentheses
+ * count plus one for the "0 capturing paren" whole text match.
+ */
+
+namespace js {
+
+struct MatchPair
+{
+    int start;
+    int limit;
+
+    MatchPair()
+      : start(-1), limit(-1)
+    { }
+
+    MatchPair(int start, int limit)
+      : start(start), limit(limit)
+    { }
+
+    size_t length()      const { JS_ASSERT(!isUndefined()); return limit - start; }
+    bool isEmpty()       const { return length() == 0; }
+    bool isUndefined()   const { return start < 0; }
+
+    void displace(size_t amount) {
+        start += (start < 0) ? 0 : amount;
+        limit += (limit < 0) ? 0 : amount;
+    }
+
+    inline bool check() const {
+        JS_ASSERT(limit >= start);
+        JS_ASSERT_IF(start < 0, start == -1);
+        JS_ASSERT_IF(limit < 0, limit == -1);
+        return true;
+    }
+};
+
+/* Base class for RegExp execution output. */
+class MatchPairs
+{
+  protected:
+    size_t     pairCount_;   /* Length of pairs_. */
+    MatchPair *pairs_;       /* Raw pointer into an allocated MatchPair buffer. */
+
+  protected:
+    /* Not used directly: use ScopedMatchPairs or VectorMatchPairs. */
+    MatchPairs()
+      : pairCount_(0), pairs_(nullptr)
+    { }
+
+  protected:
+    /* Functions used by friend classes. */
+    friend class RegExpShared;
+    friend class RegExpStatics;
+
+    /* MatchPair buffer allocator: set pairs_ and pairCount_. */
+    virtual bool allocOrExpandArray(size_t pairCount) = 0;
+
+    bool initArray(size_t pairCount);
+    bool initArrayFrom(MatchPairs &copyFrom);
+    void forgetArray() { pairs_ = nullptr; }
+
+    void displace(size_t disp);
+    void checkAgainst(size_t inputLength) {
+#ifdef DEBUG
+        for (size_t i = 0; i < pairCount_; i++) {
+            const MatchPair &p = pair(i);
+            JS_ASSERT(p.check());
+            if (p.isUndefined())
+                continue;
+            JS_ASSERT(size_t(p.limit) <= inputLength);
+        }
+#endif
+    }
+
+  public:
+    /* Querying functions in the style of RegExpStatics. */
+    bool   empty() const           { return pairCount_ == 0; }
+    size_t pairCount() const       { JS_ASSERT(pairCount_ > 0); return pairCount_; }
+    size_t parenCount() const      { return pairCount_ - 1; }
+
+  public:
+    unsigned *rawBuf() const { return reinterpret_cast<unsigned *>(pairs_); }
+    size_t length() const { return pairCount_; }
+
+    /* Pair accessors. */
+    const MatchPair &pair(size_t i) const {
+        JS_ASSERT(pairCount_ && i < pairCount_);
+        JS_ASSERT(pairs_);
+        return pairs_[i];
+    }
+
+    const MatchPair &operator[](size_t i) const { return pair(i); }
+};
+
+/* MatchPairs allocated into temporary storage, removed when out of scope. */
+class ScopedMatchPairs : public MatchPairs
+{
+    LifoAllocScope lifoScope_;
+
+  public:
+    /* Constructs an implicit LifoAllocScope. */
+    ScopedMatchPairs(LifoAlloc *lifoAlloc)
+      : lifoScope_(lifoAlloc)
+    { }
+
+    const MatchPair &operator[](size_t i) const { return pair(i); }
+
+  protected:
+    bool allocOrExpandArray(size_t pairCount);
+};
+
+/*
+ * MatchPairs allocated into permanent storage, for RegExpStatics.
+ * The Vector of MatchPairs is reusable by Vector expansion.
+ */
+class VectorMatchPairs : public MatchPairs
+{
+    Vector<MatchPair, 10, SystemAllocPolicy> vec_;
+
+  public:
+    VectorMatchPairs() {
+        vec_.clear();
+    }
+
+    const MatchPair &operator[](size_t i) const { return pair(i); }
+
+  protected:
+    friend class RegExpStatics;
+    bool allocOrExpandArray(size_t pairCount);
+};
+
+/*
+ * Passes either MatchPair or MatchPairs through ExecuteRegExp()
+ * to avoid duplication of generic code.
+ */
+struct MatchConduit
+{
+    union {
+        MatchPair  *pair;
+        MatchPairs *pairs;
+    } u;
+    bool isPair;
+
+    explicit MatchConduit(MatchPair *pair) {
+        isPair = true;
+        u.pair = pair;
+    }
+    explicit MatchConduit(MatchPairs *pairs) {
+        isPair = false;
+        u.pairs = pairs;
+    }
+};
+
+} /* namespace js */
+
+#endif /* vm_MatchPairs_h */