1 files changed, 265 insertions, 0 deletions
diff --git a/xpcom/ds/nsDeque.cpp b/xpcom/ds/nsDeque.cpp
new file mode 100644
index 0000000000..07f61fa471
--- /dev/null
+++ b/xpcom/ds/nsDeque.cpp
@@ -0,0 +1,265 @@
+/* -*- 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/. */
+
+#include "nsDeque.h"
+#include "nsISupportsImpl.h"
+#include <string.h>
+
+#include "mozilla/CheckedInt.h"
+
+#define modulus(x, y) ((x) % (y))
+
+namespace mozilla {
+namespace detail {
+
+/**
+ * Standard constructor
+ * @param deallocator, called by Erase and ~nsDequeBase
+ */
+nsDequeBase::nsDequeBase() {
+  MOZ_COUNT_CTOR(nsDequeBase);
+  mOrigin = mSize = 0;
+  mData = mBuffer;  // don't allocate space until you must
+  mCapacity = sizeof(mBuffer) / sizeof(mBuffer[0]);
+  memset(mData, 0, mCapacity * sizeof(mBuffer[0]));
+}
+
+/**
+ * Destructor
+ */
+nsDequeBase::~nsDequeBase() {
+  MOZ_COUNT_DTOR(nsDequeBase);
+
+  if (mData && mData != mBuffer) {
+    free(mData);
+  }
+  mData = nullptr;
+}
+
+size_t nsDequeBase::SizeOfExcludingThis(
+    mozilla::MallocSizeOf aMallocSizeOf) const {
+  size_t size = 0;
+  if (mData != mBuffer) {
+    size += aMallocSizeOf(mData);
+  }
+
+  return size;
+}
+
+/**
+ * Remove all items from container without destroying them.
+ */
+void nsDequeBase::Empty() {
+  if (mSize && mData) {
+    memset(mData, 0, mCapacity * sizeof(*mData));
+  }
+  mSize = 0;
+  mOrigin = 0;
+}
+
+/**
+ * This method quadruples the size of the deque
+ * Elements in the deque are resequenced so that elements
+ * in the deque are stored sequentially
+ *
+ * @return  whether growing succeeded
+ */
+bool nsDequeBase::GrowCapacity() {
+  mozilla::CheckedInt<size_t> newCapacity = mCapacity;
+  newCapacity *= 4;
+
+  NS_ASSERTION(newCapacity.isValid(), "Overflow");
+  if (!newCapacity.isValid()) {
+    return false;
+  }
+
+  // Sanity check the new byte size.
+  mozilla::CheckedInt<size_t> newByteSize = newCapacity;
+  newByteSize *= sizeof(void*);
+
+  NS_ASSERTION(newByteSize.isValid(), "Overflow");
+  if (!newByteSize.isValid()) {
+    return false;
+  }
+
+  void** temp = (void**)malloc(newByteSize.value());
+  if (!temp) {
+    return false;
+  }
+
+  // Here's the interesting part: You can't just move the elements
+  // directly (in situ) from the old buffer to the new one.
+  // Since capacity has changed, the old origin doesn't make
+  // sense anymore. It's better to resequence the elements now.
+
+  memcpy(temp, mData + mOrigin, sizeof(void*) * (mCapacity - mOrigin));
+  memcpy(temp + (mCapacity - mOrigin), mData, sizeof(void*) * mOrigin);
+
+  if (mData != mBuffer) {
+    free(mData);
+  }
+
+  mCapacity = newCapacity.value();
+  mOrigin = 0;  // now realign the origin...
+  mData = temp;
+
+  return true;
+}
+
+/**
+ * This method adds an item to the end of the deque.
+ * This operation has the potential to cause the
+ * underlying buffer to resize.
+ *
+ * @param   aItem: new item to be added to deque
+ */
+bool nsDequeBase::Push(void* aItem, const fallible_t&) {
+  if (mSize == mCapacity && !GrowCapacity()) {
+    return false;
+  }
+  mData[modulus(mOrigin + mSize, mCapacity)] = aItem;
+  mSize++;
+  return true;
+}
+
+/**
+ * This method adds an item to the front of the deque.
+ * This operation has the potential to cause the
+ * underlying buffer to resize.
+ *
+ * --Commments for GrowCapacity() case
+ * We've grown and shifted which means that the old
+ * final element in the deque is now the first element
+ * in the deque.  This is temporary.
+ * We haven't inserted the new element at the front.
+ *
+ * To continue with the idea of having the front at zero
+ * after a grow, we move the old final item (which through
+ * the voodoo of mOrigin-- is now the first) to its final
+ * position which is conveniently the old length.
+ *
+ * Note that this case only happens when the deque is full.
+ * [And that pieces of this magic only work if the deque is full.]
+ * picture:
+ *   [ABCDEFGH] @[mOrigin:3]:D.
+ * Task: PushFront("Z")
+ * shift mOrigin so, @[mOrigin:2]:C
+ * stretch and rearrange: (mOrigin:0)
+ *   [CDEFGHAB ________ ________ ________]
+ * copy: (The second C is currently out of bounds)
+ *   [CDEFGHAB C_______ ________ ________]
+ * later we will insert Z:
+ *   [ZDEFGHAB C_______ ________ ________]
+ * and increment size: 9. (C is no longer out of bounds)
+ * --
+ * @param   aItem: new item to be added to deque
+ */
+bool nsDequeBase::PushFront(void* aItem, const fallible_t&) {
+  if (mOrigin == 0) {
+    mOrigin = mCapacity - 1;
+  } else {
+    mOrigin--;
+  }
+
+  if (mSize == mCapacity) {
+    if (!GrowCapacity()) {
+      return false;
+    }
+    /* Comments explaining this are above*/
+    mData[mSize] = mData[mOrigin];
+  }
+  mData[mOrigin] = aItem;
+  mSize++;
+  return true;
+}
+
+/**
+ * Remove and return the last item in the container.
+ *
+ * @return  ptr to last item in container
+ */
+void* nsDequeBase::Pop() {
+  void* result = nullptr;
+  if (mSize > 0) {
+    --mSize;
+    size_t offset = modulus(mSize + mOrigin, mCapacity);
+    result = mData[offset];
+    mData[offset] = nullptr;
+    if (!mSize) {
+      mOrigin = 0;
+    }
+  }
+  return result;
+}
+
+/**
+ * This method gets called you want to remove and return
+ * the first member in the container.
+ *
+ * @return  last item in container
+ */
+void* nsDequeBase::PopFront() {
+  void* result = nullptr;
+  if (mSize > 0) {
+    NS_ASSERTION(mOrigin < mCapacity, "Error: Bad origin");
+    result = mData[mOrigin];
+    mData[mOrigin++] = nullptr;  // zero it out for debugging purposes.
+    mSize--;
+    // Cycle around if we pop off the end
+    // and reset origin if when we pop the last element
+    if (mCapacity == mOrigin || !mSize) {
+      mOrigin = 0;
+    }
+  }
+  return result;
+}
+
+/**
+ * This method gets called you want to peek at the bottom
+ * member without removing it.
+ *
+ * @return  last item in container
+ */
+void* nsDequeBase::Peek() const {
+  void* result = nullptr;
+  if (mSize > 0) {
+    result = mData[modulus(mSize - 1 + mOrigin, mCapacity)];
+  }
+  return result;
+}
+
+/**
+ * This method gets called you want to peek at the topmost
+ * member without removing it.
+ *
+ * @return  last item in container
+ */
+void* nsDequeBase::PeekFront() const {
+  void* result = nullptr;
+  if (mSize > 0) {
+    result = mData[mOrigin];
+  }
+  return result;
+}
+
+/**
+ * Call this to retrieve the ith element from this container.
+ * Keep in mind that accessing the underlying elements is
+ * done in a relative fashion. Object 0 is not necessarily
+ * the first element (the first element is at mOrigin).
+ *
+ * @param   aIndex : 0 relative offset of item you want
+ * @return  void* or null
+ */
+void* nsDequeBase::ObjectAt(size_t aIndex) const {
+  void* result = nullptr;
+  if (aIndex < mSize) {
+    result = mData[modulus(mOrigin + aIndex, mCapacity)];
+  }
+  return result;
+}
+}  // namespace detail
+}  // namespace mozilla