mfbt/SplayTree.h
author Morten Stenshorne <mstensho@chromium.org>
Tue, 09 Oct 2018 04:14:13 +0000
changeset 495959 13844f50ee32e17f513b7c1013c2348200e21b8c
parent 474651 ec2b59b0c7ffee3211c82df35273b4dbcbc1de44
child 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1496274 [wpt PR 13345] - [LayoutNG] Correct clip-path reference box calculation., a=testonly Automatic update from web-platform-tests[LayoutNG] Correct clip-path reference box calculation. We used coordinates relatively to the line box, while we were expected by the caller to be relative to the containing block. Flipping for writing mode was bogus for NG (but needed by legacy), since NG uses truly physical coordinates. Hardened tests to contain a leading line and padding, and leading content on the first line of the clipped child. Bug: 641907 Change-Id: I2b1b9ff4ea92a6405fcdffcf139842458b46442f Cq-Include-Trybots: luci.chromium.try​:linux_layout_tests_layout_ng Reviewed-on: https://chromium-review.googlesource.com/c/1257913 Reviewed-by: Koji Ishii <kojii@chromium.org> Reviewed-by: Fredrik Söderquist <fs@opera.com> Commit-Queue: Morten Stenshorne <mstensho@chromium.org> Cr-Commit-Position: refs/heads/master@{#596554} -- wpt-commits: e9a0828c85819340f721f121aac19ab8eefa3439 wpt-pr: 13345

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/. */

/**
 * A sorted tree with optimal access times, where recently-accessed elements
 * are faster to access again.
 */

#ifndef mozilla_SplayTree_h
#define mozilla_SplayTree_h

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"

namespace mozilla {

template<class T, class C>
class SplayTree;

template<typename T>
class SplayTreeNode
{
public:
  template<class A, class B>
  friend class SplayTree;

  SplayTreeNode()
    : mLeft(nullptr)
    , mRight(nullptr)
    , mParent(nullptr)
  {}

private:
  T* mLeft;
  T* mRight;
  T* mParent;
};


/**
 * Class which represents a splay tree.
 * Splay trees are balanced binary search trees for which search, insert and
 * remove are all amortized O(log n), but where accessing a node makes it
 * faster to access that node in the future.
 *
 * T indicates the type of tree elements, Comparator must have a static
 * compare(const T&, const T&) method ordering the elements. The compare
 * method must be free from side effects.
 */
template<typename T, class Comparator>
class SplayTree
{
  T* mRoot;

public:
  constexpr SplayTree()
    : mRoot(nullptr)
  {}

  bool empty() const
  {
    return !mRoot;
  }

  T* find(const T& aValue)
  {
    if (empty()) {
      return nullptr;
    }

    T* last = lookup(aValue);
    splay(last);
    return Comparator::compare(aValue, *last) == 0 ? last : nullptr;
  }

  void insert(T* aValue)
  {
    MOZ_ASSERT(!find(*aValue), "Duplicate elements are not allowed.");

    if (!mRoot) {
      mRoot = aValue;
      return;
    }
    T* last = lookup(*aValue);
    int cmp = Comparator::compare(*aValue, *last);

    finishInsertion(last, cmp, aValue);
  }

  T* findOrInsert(const T& aValue);

  T* remove(const T& aValue)
  {
    T* last = lookup(aValue);
    MOZ_ASSERT(last, "This tree must contain the element being removed.");
    MOZ_ASSERT(Comparator::compare(aValue, *last) == 0);

    // Splay the tree so that the item to remove is the root.
    splay(last);
    MOZ_ASSERT(last == mRoot);

    // Find another node which can be swapped in for the root: either the
    // rightmost child of the root's left, or the leftmost child of the
    // root's right.
    T* swap;
    T* swapChild;
    if (mRoot->mLeft) {
      swap = mRoot->mLeft;
      while (swap->mRight) {
        swap = swap->mRight;
      }
      swapChild = swap->mLeft;
    } else if (mRoot->mRight) {
      swap = mRoot->mRight;
      while (swap->mLeft) {
        swap = swap->mLeft;
      }
      swapChild = swap->mRight;
    } else {
      T* result = mRoot;
      mRoot = nullptr;
      return result;
    }

    // The selected node has at most one child, in swapChild. Detach it
    // from the subtree by replacing it with that child.
    if (swap == swap->mParent->mLeft) {
      swap->mParent->mLeft = swapChild;
    } else {
      swap->mParent->mRight = swapChild;
    }
    if (swapChild) {
      swapChild->mParent = swap->mParent;
    }

    // Make the selected node the new root.
    mRoot = swap;
    mRoot->mParent = nullptr;
    mRoot->mLeft = last->mLeft;
    mRoot->mRight = last->mRight;
    if (mRoot->mLeft) {
      mRoot->mLeft->mParent = mRoot;
    }
    if (mRoot->mRight) {
      mRoot->mRight->mParent = mRoot;
    }

    last->mLeft = nullptr;
    last->mRight = nullptr;
    return last;
  }

  T* removeMin()
  {
    MOZ_ASSERT(mRoot, "No min to remove!");

    T* min = mRoot;
    while (min->mLeft) {
      min = min->mLeft;
    }
    return remove(*min);
  }

  // For testing purposes only.
  void checkCoherency()
  {
    checkCoherency(mRoot, nullptr);
  }

private:
  /**
   * Returns the node in this comparing equal to |aValue|, or a node just
   * greater or just less than |aValue| if there is no such node.
   */
  T* lookup(const T& aValue)
  {
    MOZ_ASSERT(!empty());

    T* node = mRoot;
    T* parent;
    do {
      parent = node;
      int c = Comparator::compare(aValue, *node);
      if (c == 0) {
        return node;
      } else if (c < 0) {
        node = node->mLeft;
      } else {
        node = node->mRight;
      }
    } while (node);
    return parent;
  }

  void finishInsertion(T* aLast, int32_t aCmp, T* aNew)
  {
    MOZ_ASSERT(aCmp, "Nodes shouldn't be equal!");

    T** parentPointer = (aCmp < 0) ? &aLast->mLeft : &aLast->mRight;
    MOZ_ASSERT(!*parentPointer);
    *parentPointer = aNew;
    aNew->mParent = aLast;

    splay(aNew);
  }

  /**
   * Rotate the tree until |node| is at the root of the tree. Performing
   * the rotations in this fashion preserves the amortized balancing of
   * the tree.
   */
  void splay(T* aNode)
  {
    MOZ_ASSERT(aNode);

    while (aNode != mRoot) {
      T* parent = aNode->mParent;
      if (parent == mRoot) {
        // Zig rotation.
        rotate(aNode);
        MOZ_ASSERT(aNode == mRoot);
        return;
      }
      T* grandparent = parent->mParent;
      if ((parent->mLeft == aNode) == (grandparent->mLeft == parent)) {
        // Zig-zig rotation.
        rotate(parent);
        rotate(aNode);
      } else {
        // Zig-zag rotation.
        rotate(aNode);
        rotate(aNode);
      }
    }
  }

  void rotate(T* aNode)
  {
    // Rearrange nodes so that aNode becomes the parent of its current
    // parent, while preserving the sortedness of the tree.
    T* parent = aNode->mParent;
    if (parent->mLeft == aNode) {
      //     x          y
      //   y  c  ==>  a  x
      //  a b           b c
      parent->mLeft = aNode->mRight;
      if (aNode->mRight) {
        aNode->mRight->mParent = parent;
      }
      aNode->mRight = parent;
    } else {
      MOZ_ASSERT(parent->mRight == aNode);
      //   x             y
      //  a  y   ==>   x  c
      //    b c       a b
      parent->mRight = aNode->mLeft;
      if (aNode->mLeft) {
        aNode->mLeft->mParent = parent;
      }
      aNode->mLeft = parent;
    }
    aNode->mParent = parent->mParent;
    parent->mParent = aNode;
    if (T* grandparent = aNode->mParent) {
      if (grandparent->mLeft == parent) {
        grandparent->mLeft = aNode;
      } else {
        grandparent->mRight = aNode;
      }
    } else {
      mRoot = aNode;
    }
  }

  T* checkCoherency(T* aNode, T* aMinimum)
  {
    if (mRoot) {
      MOZ_RELEASE_ASSERT(!mRoot->mParent);
    }
    if (!aNode) {
      MOZ_RELEASE_ASSERT(!mRoot);
      return nullptr;
    }
    if (!aNode->mParent) {
      MOZ_RELEASE_ASSERT(aNode == mRoot);
    }
    if (aMinimum) {
      MOZ_RELEASE_ASSERT(Comparator::compare(*aMinimum, *aNode) < 0);
    }
    if (aNode->mLeft) {
      MOZ_RELEASE_ASSERT(aNode->mLeft->mParent == aNode);
      T* leftMaximum = checkCoherency(aNode->mLeft, aMinimum);
      MOZ_RELEASE_ASSERT(Comparator::compare(*leftMaximum, *aNode) < 0);
    }
    if (aNode->mRight) {
      MOZ_RELEASE_ASSERT(aNode->mRight->mParent == aNode);
      return checkCoherency(aNode->mRight, aNode);
    }
    return aNode;
  }

  SplayTree(const SplayTree&) = delete;
  void operator=(const SplayTree&) = delete;
};

template<typename T, class Comparator>
T*
SplayTree<T, Comparator>::findOrInsert(const T& aValue)
{
  if (!mRoot) {
    mRoot = new T(aValue);
    return mRoot;
  }

  T* last = lookup(aValue);
  int cmp = Comparator::compare(aValue, *last);
  if (!cmp) {
    return last;
  }

  T* t = new T(aValue);
  finishInsertion(last, cmp, t);
  return t;
}

}  /* namespace mozilla */

#endif /* mozilla_SplayTree_h */