Migrate the IndexedDB backend from Blink to Chromium

content/browser/indexed_db/leveldb/avltree.h

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/*
+ * Copyright (C) 2008 Apple Inc. All rights reserved.
+ *
+ * Based on Abstract AVL Tree Template v1.5 by Walt Karas
+ * <http://geocities.com/wkaras/gen_cpp/avl_tree.html>.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CONTENT_BROWSER_INDEXED_DB_LEVELDB_AVLTREE_H_
+#define CONTENT_BROWSER_INDEXED_DB_LEVELDB_AVLTREE_H_
+
+#include "base/logging.h"
+#include "content/browser/indexed_db/leveldb/fixed_array.h"
+
+namespace content {
+
+// Here is the reference class for BSet.
+//
+// class BSet
+//   {
+//   public:
+//
+//     class ANY_bitref
+//       {
+//       public:
+//         operator bool ();
+//         void operator = (bool b);
+//       };
+//
+//     // Does not have to initialize bits.
+//     BSet();
+//
+//     // Must return a valid value for index when 0 <= index < maxDepth
+//     ANY_bitref operator [] (unsigned index);
+//
+//     // Set all bits to 1.
+//     void set();
+//
+//     // Set all bits to 0.
+//     void reset();
+//   };
+
+template <unsigned maxDepth> class AVLTreeDefaultBSet {
+ public:
+  bool& operator[](unsigned i) {
+#if defined(ADDRESS_SANITIZER)
+    CHECK(i < maxDepth);
+#endif
+    return m_data[i];
+  }
+  void set() {
+    for (unsigned i = 0; i < maxDepth; ++i)
+      m_data[i] = true;
+  }
+  void reset() {
+    for (unsigned i = 0; i < maxDepth; ++i)
+      m_data[i] = false;
+  }
+
+ private:
+  FixedArray<bool, maxDepth> m_data;
+};
+
+// How to determine maxDepth:
+// d  Minimum number of nodes
+// 2  2
+// 3  4
+// 4  7
+// 5  12
+// 6  20
+// 7  33
+// 8  54
+// 9  88
+// 10 143
+// 11 232
+// 12 376
+// 13 609
+// 14 986
+// 15 1,596
+// 16 2,583
+// 17 4,180
+// 18 6,764
+// 19 10,945
+// 20 17,710
+// 21 28,656
+// 22 46,367
+// 23 75,024
+// 24 121,392
+// 25 196,417
+// 26 317,810
+// 27 514,228
+// 28 832,039
+// 29 1,346,268
+// 30 2,178,308
+// 31 3,524,577
+// 32 5,702,886
+// 33 9,227,464
+// 34 14,930,351
+// 35 24,157,816
+// 36 39,088,168
+// 37 63,245,985
+// 38 102,334,154
+// 39 165,580,140
+// 40 267,914,295
+// 41 433,494,436
+// 42 701,408,732
+// 43 1,134,903,169
+// 44 1,836,311,902
+// 45 2,971,215,072
+//
+// E.g., if, in a particular instantiation, the maximum number of nodes in a
+// tree instance is 1,000,000, the maximum depth should be 28.
+// You pick 28 because MN(28) is 832,039, which is less than or equal to
+// 1,000,000, and MN(29) is 1,346,268, which is strictly greater than 1,000,000.
+
+template <class Abstractor,
+          unsigned maxDepth = 32,
+          class BSet = AVLTreeDefaultBSet<maxDepth> >
+class AVLTree {
+ public:
+  typedef typename Abstractor::key key;
+  typedef typename Abstractor::handle handle;
+  typedef typename Abstractor::size size;
+
+  enum SearchType {
+    EQUAL = 1,
+    LESS = 2,
+    GREATER = 4,
+    LESS_EQUAL = EQUAL | LESS,
+    GREATER_EQUAL = EQUAL | GREATER
+  };
+
+  Abstractor& abstractor() { return abs; }
+
+  inline handle insert(handle h);
+
+  inline handle search(key k, SearchType st = EQUAL);
+  inline handle search_least();
+  inline handle search_greatest();
+
+  inline handle remove(key k);
+
+  inline handle subst(handle new_node);
+
+  void purge() { abs.root = null(); }
+
+  bool is_empty() { return abs.root == null(); }
+
+  AVLTree() { abs.root = null(); }
+
+  class Iterator {
+   public:
+    // Initialize depth to invalid value, to indicate iterator is
+    // invalid.   (Depth is zero-base.)
+    Iterator() { depth = ~0U; }
+
+    void start_iter(AVLTree& tree, key k, SearchType st = EQUAL) {
+      // Mask of high bit in an int.
+      const int kMaskHighBit = (int) ~((~(unsigned) 0) >> 1);
+
+      // Save the tree that we're going to iterate through in a
+      // member variable.
+      tree_ = &tree;
+
+      int cmp, target_cmp;
+      handle h = tree_->abs.root;
+      unsigned d = 0;
+
+      depth = ~0U;
+
+      if (h == null()) {
+        // Tree is empty.
+        return;
+      }
+
+      if (st & LESS) {
+        // Key can be greater than key of starting node.
+        target_cmp = 1;
+      } else if (st & GREATER) {
+        // Key can be less than key of starting node.
+        target_cmp = -1;
+      } else {
+        // Key must be same as key of starting node.
+        target_cmp = 0;
+      }
+
+      for (;;) {
+        cmp = cmp_k_n(k, h);
+        if (cmp == 0) {
+          if (st & EQUAL) {
+            // Equal node was sought and found as starting node.
+            depth = d;
+            break;
+          }
+          cmp = -target_cmp;
+        } else if (target_cmp != 0) {
+          if (!((cmp ^ target_cmp) & kMaskHighBit)) {
+            // cmp and target_cmp are both negative or both positive.
+            depth = d;
+          }
+        }
+        h = cmp < 0 ? get_lt(h) : get_gt(h);
+        if (h == null())
+          break;
+        branch[d] = cmp > 0;
+        path_h[d++] = h;
+      }
+    }
+
+    void start_iter_least(AVLTree& tree) {
+      tree_ = &tree;
+
+      handle h = tree_->abs.root;
+
+      depth = ~0U;
+
+      branch.reset();
+
+      while (h != null()) {
+        if (depth != ~0U)
+          path_h[depth] = h;
+        depth++;
+        h = get_lt(h);
+      }
+    }
+
+    void start_iter_greatest(AVLTree& tree) {
+      tree_ = &tree;
+
+      handle h = tree_->abs.root;
+
+      depth = ~0U;
+
+      branch.set();
+
+      while (h != null()) {
+        if (depth != ~0U)
+          path_h[depth] = h;
+        depth++;
+        h = get_gt(h);
+      }
+    }
+
+    handle operator*() {
+      if (depth == ~0U)
+        return null();
+
+      return depth == 0 ? tree_->abs.root : path_h[depth - 1];
+    }
+
+    void operator++() {
+      if (depth != ~0U) {
+        handle h = get_gt(**this);
+        if (h == null()) {
+          do {
+            if (depth == 0) {
+              depth = ~0U;
+              break;
+            }
+            depth--;
+          } while (branch[depth]);
+        } else {
+          branch[depth] = true;
+          path_h[depth++] = h;
+          for (;;) {
+            h = get_lt(h);
+            if (h == null())
+              break;
+            branch[depth] = false;
+            path_h[depth++] = h;
+          }
+        }
+      }
+    }
+
+    void operator--() {
+      if (depth != ~0U) {
+        handle h = get_lt(**this);
+        if (h == null()) {
+          do {
+            if (depth == 0) {
+              depth = ~0U;
+              break;
+            }
+            depth--;
+          } while (!branch[depth]);
+        } else {
+          branch[depth] = false;
+          path_h[depth++] = h;
+          for (;;) {
+            h = get_gt(h);
+            if (h == null())
+              break;
+            branch[depth] = true;
+            path_h[depth++] = h;
+          }
+        }
+      }
+    }
+
+    void operator++(int) { ++(*this); }
+    void operator--(int) { --(*this); }
+
+   protected:
+
+    // Tree being iterated over.
+    AVLTree* tree_;
+
+    // Records a path into the tree.  If branch[n] is true, indicates
+    // take greater branch from the nth node in the path, otherwise
+    // take the less branch.  branch[0] gives branch from root, and
+    // so on.
+    BSet branch;
+
+    // Zero-based depth of path into tree.
+    unsigned depth;
+
+    // Handles of nodes in path from root to current node (returned by *).
+    handle path_h[maxDepth - 1];
+
+    int cmp_k_n(key k, handle h) { return tree_->abs.compare_key_node(k, h); }
+    int cmp_n_n(handle h1, handle h2) {
+      return tree_->abs.compare_node_node(h1, h2);
+    }
+    handle get_lt(handle h) { return tree_->abs.get_less(h); }
+    handle get_gt(handle h) { return tree_->abs.get_greater(h); }
+    handle null() { return tree_->abs.null(); }
+  };
+
+  template <typename fwd_iter> bool build(fwd_iter p, size num_nodes) {
+    if (num_nodes == 0) {
+      abs.root = null();
+      return true;
+    }
+
+    // Gives path to subtree being built.  If branch[N] is false, branch
+    // less from the node at depth N, if true branch greater.
+    BSet branch;
+
+    // If rem[N] is true, then for the current subtree at depth N, it's
+    // greater subtree has one more node than it's less subtree.
+    BSet rem;
+
+    // Depth of root node of current subtree.
+    unsigned depth = 0;
+
+    // Number of nodes in current subtree.
+    size num_sub = num_nodes;
+
+    // The algorithm relies on a stack of nodes whose less subtree has
+    // been built, but whose right subtree has not yet been built.  The
+    // stack is implemented as linked list.  The nodes are linked
+    // together by having the "greater" handle of a node set to the
+    // next node in the list.  "less_parent" is the handle of the first
+    // node in the list.
+    handle less_parent = null();
+
+    // h is root of current subtree, child is one of its children.
+    handle h, child;
+
+    for (;;) {
+      while (num_sub > 2) {
+        // Subtract one for root of subtree.
+        num_sub--;
+        rem[depth] = !!(num_sub & 1);
+        branch[depth++] = false;
+        num_sub >>= 1;
+      }
+
+      if (num_sub == 2) {
+        // Build a subtree with two nodes, slanting to greater.
+        // I arbitrarily chose to always have the extra node in the
+        // greater subtree when there is an odd number of nodes to
+        // split between the two subtrees.
+
+        h = *p;
+        p++;
+        child = *p;
+        p++;
+        set_lt(child, null());
+        set_gt(child, null());
+        set_bf(child, 0);
+        set_gt(h, child);
+        set_lt(h, null());
+        set_bf(h, 1);
+      } else {  // num_sub == 1
+                // Build a subtree with one node.
+
+        h = *p;
+        p++;
+        set_lt(h, null());
+        set_gt(h, null());
+        set_bf(h, 0);
+      }
+
+      while (depth) {
+        depth--;
+        if (!branch[depth]) {
+          // We've completed a less subtree.
+          break;
+        }
+
+        // We've completed a greater subtree, so attach it to
+        // its parent (that is less than it).  We pop the parent
+        // off the stack of less parents.
+        child = h;
+        h = less_parent;
+        less_parent = get_gt(h);
+        set_gt(h, child);
+        // num_sub = 2 * (num_sub - rem[depth]) + rem[depth] + 1
+        num_sub <<= 1;
+        num_sub += 1 - rem[depth];
+        if (num_sub & (num_sub - 1)) {
+          // num_sub is not a power of 2
+          set_bf(h, 0);
+        } else {
+          // num_sub is a power of 2
+          set_bf(h, 1);
+        }
+      }
+
+      if (num_sub == num_nodes) {
+        // We've completed the full tree.
+        break;
+      }
+
+      // The subtree we've completed is the less subtree of the
+      // next node in the sequence.
+
+      child = h;
+      h = *p;
+      p++;
+      set_lt(h, child);
+
+      // Put h into stack of less parents.
+      set_gt(h, less_parent);
+      less_parent = h;
+
+      // Proceed to creating greater than subtree of h.
+      branch[depth] = true;
+      num_sub += rem[depth++];
+
+    }  // end for (;;)
+
+    abs.root = h;
+
+    return true;
+  }
+
+ protected:
+
+  friend class Iterator;
+
+  // Create a class whose sole purpose is to take advantage of
+  // the "empty member" optimization.
+  struct abs_plus_root : public Abstractor {
+    // The handle of the root element in the AVL tree.
+    handle root;
+  };
+
+  abs_plus_root abs;
+
+  handle get_lt(handle h) { return abs.get_less(h); }
+  void set_lt(handle h, handle lh) { abs.set_less(h, lh); }
+
+  handle get_gt(handle h) { return abs.get_greater(h); }
+  void set_gt(handle h, handle gh) { abs.set_greater(h, gh); }
+
+  int get_bf(handle h) { return abs.get_balance_factor(h); }
+  void set_bf(handle h, int bf) { abs.set_balance_factor(h, bf); }
+
+  int cmp_k_n(key k, handle h) { return abs.compare_key_node(k, h); }
+  int cmp_n_n(handle h1, handle h2) { return abs.compare_node_node(h1, h2); }
+
+  handle null() { return abs.null(); }
+
+ private:
+
+  // Balances subtree, returns handle of root node of subtree
+  // after balancing.
+  handle balance(handle bal_h) {
+    handle deep_h;
+
+    // Either the "greater than" or the "less than" subtree of
+    // this node has to be 2 levels deeper (or else it wouldn't
+    // need balancing).
+
+    if (get_bf(bal_h) > 0) {
+      // "Greater than" subtree is deeper.
+
+      deep_h = get_gt(bal_h);
+
+      if (get_bf(deep_h) < 0) {
+        handle old_h = bal_h;
+        bal_h = get_lt(deep_h);
+
+        set_gt(old_h, get_lt(bal_h));
+        set_lt(deep_h, get_gt(bal_h));
+        set_lt(bal_h, old_h);
+        set_gt(bal_h, deep_h);
+
+        int bf = get_bf(bal_h);
+        if (bf != 0) {
+          if (bf > 0) {
+            set_bf(old_h, -1);
+            set_bf(deep_h, 0);
+          } else {
+            set_bf(deep_h, 1);
+            set_bf(old_h, 0);
+          }
+          set_bf(bal_h, 0);
+        } else {
+          set_bf(old_h, 0);
+          set_bf(deep_h, 0);
+        }
+      } else {
+        set_gt(bal_h, get_lt(deep_h));
+        set_lt(deep_h, bal_h);
+        if (get_bf(deep_h) == 0) {
+          set_bf(deep_h, -1);
+          set_bf(bal_h, 1);
+        } else {
+          set_bf(deep_h, 0);
+          set_bf(bal_h, 0);
+        }
+        bal_h = deep_h;
+      }
+    } else {
+      // "Less than" subtree is deeper.
+
+      deep_h = get_lt(bal_h);
+
+      if (get_bf(deep_h) > 0) {
+        handle old_h = bal_h;
+        bal_h = get_gt(deep_h);
+        set_lt(old_h, get_gt(bal_h));
+        set_gt(deep_h, get_lt(bal_h));
+        set_gt(bal_h, old_h);
+        set_lt(bal_h, deep_h);
+
+        int bf = get_bf(bal_h);
+        if (bf != 0) {
+          if (bf < 0) {
+            set_bf(old_h, 1);
+            set_bf(deep_h, 0);
+          } else {
+            set_bf(deep_h, -1);
+            set_bf(old_h, 0);
+          }
+          set_bf(bal_h, 0);
+        } else {
+          set_bf(old_h, 0);
+          set_bf(deep_h, 0);
+        }
+      } else {
+        set_lt(bal_h, get_gt(deep_h));
+        set_gt(deep_h, bal_h);
+        if (get_bf(deep_h) == 0) {
+          set_bf(deep_h, 1);
+          set_bf(bal_h, -1);
+        } else {
+          set_bf(deep_h, 0);
+          set_bf(bal_h, 0);
+        }
+        bal_h = deep_h;
+      }
+    }
+
+    return bal_h;
+  }
+
+};
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::insert(handle h) {
+  set_lt(h, null());
+  set_gt(h, null());
+  set_bf(h, 0);
+
+  if (abs.root == null()) {
+    abs.root = h;
+  } else {
+    // Last unbalanced node encountered in search for insertion point.
+    handle unbal = null();
+    // Parent of last unbalanced node.
+    handle parent_unbal = null();
+    // Balance factor of last unbalanced node.
+    int unbal_bf;
+
+    // Zero-based depth in tree.
+    unsigned depth = 0, unbal_depth = 0;
+
+    // Records a path into the tree.  If branch[n] is true, indicates
+    // take greater branch from the nth node in the path, otherwise
+    // take the less branch.  branch[0] gives branch from root, and
+    // so on.
+    BSet branch;
+
+    handle hh = abs.root;
+    handle parent = null();
+    int cmp;
+
+    do {
+      if (get_bf(hh) != 0) {
+        unbal = hh;
+        parent_unbal = parent;
+        unbal_depth = depth;
+      }
+      cmp = cmp_n_n(h, hh);
+      if (cmp == 0) {
+        // Duplicate key.
+        return hh;
+      }
+      parent = hh;
+      hh = cmp < 0 ? get_lt(hh) : get_gt(hh);
+      branch[depth++] = cmp > 0;
+    } while (hh != null());
+
+    //  Add node to insert as leaf of tree.
+    if (cmp < 0)
+      set_lt(parent, h);
+    else
+      set_gt(parent, h);
+
+    depth = unbal_depth;
+
+    if (unbal == null()) {
+      hh = abs.root;
+    } else {
+      cmp = branch[depth++] ? 1 : -1;
+      unbal_bf = get_bf(unbal);
+      if (cmp < 0)
+        unbal_bf--;
+      else  // cmp > 0
+        unbal_bf++;
+      hh = cmp < 0 ? get_lt(unbal) : get_gt(unbal);
+      if ((unbal_bf != -2) && (unbal_bf != 2)) {
+        // No rebalancing of tree is necessary.
+        set_bf(unbal, unbal_bf);
+        unbal = null();
+      }
+    }
+
+    if (hh != null()) {
+      while (h != hh) {
+        cmp = branch[depth++] ? 1 : -1;
+        if (cmp < 0) {
+          set_bf(hh, -1);
+          hh = get_lt(hh);
+        } else {  // cmp > 0
+          set_bf(hh, 1);
+          hh = get_gt(hh);
+        }
+      }
+    }
+
+    if (unbal != null()) {
+      unbal = balance(unbal);
+      if (parent_unbal == null()) {
+        abs.root = unbal;
+      } else {
+        depth = unbal_depth - 1;
+        cmp = branch[depth] ? 1 : -1;
+        if (cmp < 0)
+          set_lt(parent_unbal, unbal);
+        else  // cmp > 0
+          set_gt(parent_unbal, unbal);
+      }
+    }
+  }
+
+  return h;
+}
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::search(
+    key k,
+    typename AVLTree<Abstractor, maxDepth, BSet>::SearchType st) {
+  const int kMaskHighBit = (int) ~((~(unsigned) 0) >> 1);
+
+  int cmp, target_cmp;
+  handle match_h = null();
+  handle h = abs.root;
+
+  if (st & LESS)
+    target_cmp = 1;
+  else if (st & GREATER)
+    target_cmp = -1;
+  else
+    target_cmp = 0;
+
+  while (h != null()) {
+    cmp = cmp_k_n(k, h);
+    if (cmp == 0) {
+      if (st & EQUAL) {
+        match_h = h;
+        break;
+      }
+      cmp = -target_cmp;
+    } else if (target_cmp != 0) {
+      if (!((cmp ^ target_cmp) & kMaskHighBit)) {
+        // cmp and target_cmp are both positive or both negative.
+        match_h = h;
+      }
+    }
+    h = cmp < 0 ? get_lt(h) : get_gt(h);
+  }
+
+  return match_h;
+}
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::search_least() {
+  handle h = abs.root, parent = null();
+
+  while (h != null()) {
+    parent = h;
+    h = get_lt(h);
+  }
+
+  return parent;
+}
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::search_greatest() {
+  handle h = abs.root, parent = null();
+
+  while (h != null()) {
+    parent = h;
+    h = get_gt(h);
+  }
+
+  return parent;
+}
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::remove(key k) {
+  // Zero-based depth in tree.
+  unsigned depth = 0, rm_depth;
+
+  // Records a path into the tree.  If branch[n] is true, indicates
+  // take greater branch from the nth node in the path, otherwise
+  // take the less branch.  branch[0] gives branch from root, and
+  // so on.
+  BSet branch;
+
+  handle h = abs.root;
+  handle parent = null(), child;
+  int cmp, cmp_shortened_sub_with_path = 0;
+
+  for (;;) {
+    if (h == null()) {
+      // No node in tree with given key.
+      return null();
+    }
+    cmp = cmp_k_n(k, h);
+    if (cmp == 0) {
+      // Found node to remove.
+      break;
+    }
+    parent = h;
+    h = cmp < 0 ? get_lt(h) : get_gt(h);
+    branch[depth++] = cmp > 0;
+    cmp_shortened_sub_with_path = cmp;
+  }
+  handle rm = h;
+  handle parent_rm = parent;
+  rm_depth = depth;
+
+  // If the node to remove is not a leaf node, we need to get a
+  // leaf node, or a node with a single leaf as its child, to put
+  // in the place of the node to remove.  We will get the greatest
+  // node in the less subtree (of the node to remove), or the least
+  // node in the greater subtree.  We take the leaf node from the
+  // deeper subtree, if there is one.
+
+  if (get_bf(h) < 0) {
+    child = get_lt(h);
+    branch[depth] = false;
+    cmp = -1;
+  } else {
+    child = get_gt(h);
+    branch[depth] = true;
+    cmp = 1;
+  }
+  depth++;
+
+  if (child != null()) {
+    cmp = -cmp;
+    do {
+      parent = h;
+      h = child;
+      if (cmp < 0) {
+        child = get_lt(h);
+        branch[depth] = false;
+      } else {
+        child = get_gt(h);
+        branch[depth] = true;
+      }
+      depth++;
+    } while (child != null());
+
+    if (parent == rm) {
+      // Only went through do loop once.  Deleted node will be replaced
+      // in the tree structure by one of its immediate children.
+      cmp_shortened_sub_with_path = -cmp;
+    } else {
+      cmp_shortened_sub_with_path = cmp;
+    }
+
+    // Get the handle of the opposite child, which may not be null.
+    child = cmp > 0 ? get_lt(h) : get_gt(h);
+  }
+
+  if (parent == null()) {
+    // There were only 1 or 2 nodes in this tree.
+    abs.root = child;
+  } else if (cmp_shortened_sub_with_path < 0) {
+    set_lt(parent, child);
+  } else {
+    set_gt(parent, child);
+  }
+
+  // "path" is the parent of the subtree being eliminated or reduced
+  // from a depth of 2 to 1.  If "path" is the node to be removed, we
+  // set path to the node we're about to poke into the position of the
+  // node to be removed.
+  handle path = parent == rm ? h : parent;
+
+  if (h != rm) {
+    // Poke in the replacement for the node to be removed.
+    set_lt(h, get_lt(rm));
+    set_gt(h, get_gt(rm));
+    set_bf(h, get_bf(rm));
+    if (parent_rm == null()) {
+      abs.root = h;
+    } else {
+      depth = rm_depth - 1;
+      if (branch[depth])
+        set_gt(parent_rm, h);
+      else
+        set_lt(parent_rm, h);
+    }
+  }
+
+  if (path != null()) {
+    // Create a temporary linked list from the parent of the path node
+    // to the root node.
+    h = abs.root;
+    parent = null();
+    depth = 0;
+    while (h != path) {
+      if (branch[depth++]) {
+        child = get_gt(h);
+        set_gt(h, parent);
+      } else {
+        child = get_lt(h);
+        set_lt(h, parent);
+      }
+      parent = h;
+      h = child;
+    }
+
+    // Climb from the path node to the root node using the linked
+    // list, restoring the tree structure and rebalancing as necessary.
+    bool reduced_depth = true;
+    int bf;
+    cmp = cmp_shortened_sub_with_path;
+    for (;;) {
+      if (reduced_depth) {
+        bf = get_bf(h);
+        if (cmp < 0)
+          bf++;
+        else  // cmp > 0
+          bf--;
+        if ((bf == -2) || (bf == 2)) {
+          h = balance(h);
+          bf = get_bf(h);
+        } else {
+          set_bf(h, bf);
+        }
+        reduced_depth = (bf == 0);
+      }
+      if (parent == null())
+        break;
+      child = h;
+      h = parent;
+      cmp = branch[--depth] ? 1 : -1;
+      if (cmp < 0) {
+        parent = get_lt(h);
+        set_lt(h, child);
+      } else {
+        parent = get_gt(h);
+        set_gt(h, child);
+      }
+    }
+    abs.root = h;
+  }
+
+  return rm;
+}
+
+template <class Abstractor, unsigned maxDepth, class BSet>
+inline typename AVLTree<Abstractor, maxDepth, BSet>::handle
+AVLTree<Abstractor, maxDepth, BSet>::subst(handle new_node) {
+  handle h = abs.root;
+  handle parent = null();
+  int cmp, last_cmp;
+
+  // Search for node already in tree with same key.
+  for (;;) {
+    if (h == null()) {
+      // No node in tree with same key as new node.
+      return null();
+    }
+    cmp = cmp_n_n(new_node, h);
+    if (cmp == 0) {
+      // Found the node to substitute new one for.
+      break;
+    }
+    last_cmp = cmp;
+    parent = h;
+    h = cmp < 0 ? get_lt(h) : get_gt(h);
+  }
+
+  // Copy tree housekeeping fields from node in tree to new node.
+  set_lt(new_node, get_lt(h));
+  set_gt(new_node, get_gt(h));
+  set_bf(new_node, get_bf(h));
+
+  if (parent == null()) {
+    // New node is also new root.
+    abs.root = new_node;
+  } else {
+    // Make parent point to new node.
+    if (last_cmp < 0)
+      set_lt(parent, new_node);
+    else
+      set_gt(parent, new_node);
+  }
+
+  return h;
+}
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_INDEXED_DB_LEVELDB_AVLTREE_H_