gecko-dev/xpcom/glue/nsDeque.cpp

/* -*- 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>
#ifdef DEBUG_rickg
#include <stdio.h>
#endif

#include "mozilla/CheckedInt.h"

/**
 * 07/02/2001  09:17p 509,104 clangref.pdf from openwatcom's site
 * Watcom C Language Reference Edition 11.0c
 * page 118 of 297
 *
 * The % symbol yields the remainder from the division of the first operand
 * by the second operand. The operands of % must have integral type.
 *
 * When both operands of % are positive, the result is a positive value
 * smaller than the second operand. When one or both operands is negative,
 * whether the result is positive or negative is implementation-defined.
 *
 */
/* Ok, so first of all, C is underspecified. joy.
 * The following functions do not provide a correct implementation of modulus
 * They provide functionality for x>-y.
 * There are risks of 2*y being greater than max int, which is part of the
 * reason no multiplication is used and other operations are avoided.
 *
 * modasgn
 * @param x variable
 * @param y expression
 * approximately equivalent to x %= y
 *
 * modulus
 * @param x expression
 * @param y expression
 * approximately equivalent to x % y
 */
#define modasgn(x,y) if (x<0) x+=y; x%=y
#define modulus(x,y) ((x<0)?(x+y)%(y):(x)%(y))

/**
 * Standard constructor
 * @param deallocator, called by Erase and ~nsDeque
 */
nsDeque::nsDeque(nsDequeFunctor* aDeallocator)
{
  MOZ_COUNT_CTOR(nsDeque);
  mDeallocator = aDeallocator;
  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
 */
nsDeque::~nsDeque()
{
  MOZ_COUNT_DTOR(nsDeque);

#ifdef DEBUG_rickg
  char buffer[30];
  printf("Capacity: %i\n", mCapacity);

  static int mCaps[15] = {0};
  switch (mCapacity) {
    case 4:     mCaps[0]++; break;
    case 8:     mCaps[1]++; break;
    case 16:    mCaps[2]++; break;
    case 32:    mCaps[3]++; break;
    case 64:    mCaps[4]++; break;
    case 128:   mCaps[5]++; break;
    case 256:   mCaps[6]++; break;
    case 512:   mCaps[7]++; break;
    case 1024:  mCaps[8]++; break;
    case 2048:  mCaps[9]++; break;
    case 4096:  mCaps[10]++; break;
    default:
      break;
  }
#endif

  Erase();
  if (mData && mData != mBuffer) {
    free(mData);
  }
  mData = 0;
  SetDeallocator(0);
}

size_t
nsDeque::SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
  size_t size = 0;
  if (mData != mBuffer) {
    size += aMallocSizeOf(mData);
  }

  if (mDeallocator) {
    size += aMallocSizeOf(mDeallocator);
  }

  return size;
}

size_t
nsDeque::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
  return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
}

/**
 * Set the functor to be called by Erase()
 * The deque owns the functor.
 *
 * @param   aDeallocator functor object for use by Erase()
 */
void
nsDeque::SetDeallocator(nsDequeFunctor* aDeallocator)
{
  delete mDeallocator;
  mDeallocator = aDeallocator;
}

/**
 * Remove all items from container without destroying them.
 */
void
nsDeque::Empty()
{
  if (mSize && mData) {
    memset(mData, 0, mCapacity * sizeof(*mData));
  }
  mSize = 0;
  mOrigin = 0;
}

/**
 * Remove and delete all items from container
 */
void
nsDeque::Erase()
{
  if (mDeallocator && mSize) {
    ForEach(*mDeallocator);
  }
  Empty();
}

/**
 * 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
nsDeque::GrowCapacity()
{
  mozilla::CheckedInt<int32_t> newCapacity = mCapacity;
  newCapacity *= 4;

  NS_ASSERTION(newCapacity.isValid(), "Overflow");
  if (!newCapacity.isValid()) {
    return false;
  }

  // Sanity check the new byte size.
  mozilla::CheckedInt<int32_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
nsDeque::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
nsDeque::PushFront(void* aItem, const fallible_t&)
{
  mOrigin--;
  modasgn(mOrigin, mCapacity);
  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*
nsDeque::Pop()
{
  void* result = 0;
  if (mSize > 0) {
    --mSize;
    int32_t offset = modulus(mSize + mOrigin, mCapacity);
    result = mData[offset];
    mData[offset] = 0;
    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*
nsDeque::PopFront()
{
  void* result = 0;
  if (mSize > 0) {
    NS_ASSERTION(mOrigin < mCapacity, "Error: Bad origin");
    result = mData[mOrigin];
    mData[mOrigin++] = 0;   //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*
nsDeque::Peek()
{
  void* result = 0;
  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*
nsDeque::PeekFront()
{
  void* result = 0;
  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*
nsDeque::ObjectAt(int32_t aIndex) const
{
  void* result = 0;
  if (aIndex >= 0 && aIndex < mSize) {
    result = mData[modulus(mOrigin + aIndex, mCapacity)];
  }
  return result;
}

void*
nsDeque::RemoveObjectAt(int32_t aIndex)
{
  if (aIndex < 0 || aIndex >= mSize) {
    return 0;
  }
  void* result = mData[modulus(mOrigin + aIndex, mCapacity)];

  // "Shuffle down" all elements in the array by 1, overwritting the element
  // being removed.
  for (int32_t i = aIndex; i < mSize; ++i) {
    mData[modulus(mOrigin + i, mCapacity)] =
      mData[modulus(mOrigin + i + 1, mCapacity)];
  }
  mSize--;

  return result;
}

void*
nsDeque::Last() const
{
  return ObjectAt(mSize - 1);
}

/**
 * Call this method when you want to iterate all the
 * members of the container, passing a functor along
 * to call your code.
 *
 * @param   aFunctor object to call for each member
 * @return  *this
 */
void
nsDeque::ForEach(nsDequeFunctor& aFunctor) const
{
  for (int32_t i = 0; i < mSize; ++i) {
    aFunctor(ObjectAt(i));
  }
}

/**
 * Call this method when you want to iterate all the
 * members of the container, calling the functor you
 * passed with each member. This process will interrupt
 * if your function returns non 0 to this method.
 *
 * @param   aFunctor object to call for each member
 * @return  first nonzero result of aFunctor or 0.
 */
const void*
nsDeque::FirstThat(nsDequeFunctor& aFunctor) const
{
  for (int32_t i = 0; i < mSize; ++i) {
    void* obj = aFunctor(ObjectAt(i));
    if (obj) {
      return obj;
    }
  }
  return 0;
}