gecko-dev/xpcom/glue/nsDeque.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 "nsCRT.h"
#ifdef DEBUG_rickg
#include <stdio.h>
#endif

/**
 * 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] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
  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);
}

/**
 * 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() {
  int32_t theNewSize=mCapacity<<2;
  NS_ASSERTION(theNewSize>mCapacity, "Overflow");
  if (theNewSize<=mCapacity)
    return false;
  void** temp=(void**)malloc(theNewSize * sizeof(void*));
  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=theNewSize;
  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;
}

/**
 * Create and return an iterator pointing to
 * the beginning of the queue. Note that this
 * takes the circular buffer semantics into account.
 *
 * @return  new deque iterator, init'ed to 1st item
 */
nsDequeIterator nsDeque::Begin() const{
  return nsDequeIterator(*this, 0);
}

/**
 * Create and return an iterator pointing to
 * the last item in the deque.
 * Note that this takes the circular buffer semantics
 * into account.
 *
 * @return  new deque iterator, init'ed to the last item
 */
nsDequeIterator nsDeque::End() const{
  return nsDequeIterator(*this, mSize - 1);
}

void* nsDeque::Last() const {
  return End().GetCurrent();
}

/**
 * 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;
}

/******************************************************
 * Here comes the nsDequeIterator class...
 ******************************************************/

/**
 * DequeIterator is an object that knows how to iterate (forward and backward)
 * through a Deque. Normally, you don't need to do this, but there are some special
 * cases where it is pretty handy, so here you go.
 *
 * This is a standard dequeiterator constructor
 *
 * @param   aQueue is the deque object to be iterated
 * @param   aIndex is the starting position for your iteration
 */
nsDequeIterator::nsDequeIterator(const nsDeque& aQueue, int aIndex)
: mIndex(aIndex),
  mDeque(aQueue)
{
}

/**
 * Create a copy of a DequeIterator
 *
 * @param   aCopy is another iterator to copy from
 */
nsDequeIterator::nsDequeIterator(const nsDequeIterator& aCopy)
: mIndex(aCopy.mIndex),
  mDeque(aCopy.mDeque)
{
}

/**
 * Moves iterator to first element in deque
 * @return  *this
 */
nsDequeIterator& nsDequeIterator::First(){
  mIndex=0;
  return *this;
}

/**
 * Standard assignment operator for dequeiterator
 *
 * @param   aCopy is an iterator to be copied from
 * @return  *this
 */
nsDequeIterator& nsDequeIterator::operator=(const nsDequeIterator& aCopy) {
  NS_ASSERTION(&mDeque==&aCopy.mDeque,"you can't change the deque that an interator is iterating over, sorry.");
  mIndex=aCopy.mIndex;
  return *this;
}

/**
 * preform ! operation against to iterators to test for equivalence
 * (or lack thereof)!
 *
 * @param   aIter is the object to be compared to
 * @return  TRUE if NOT equal.
 */
bool nsDequeIterator::operator!=(nsDequeIterator& aIter) {
  return bool(!this->operator==(aIter));
}

/**
 * Compare two iterators for increasing order.
 *
 * @param   aIter is the other iterator to be compared to
 * @return  TRUE if this object points to an element before
 *          the element pointed to by aIter.
 *          FALSE if this and aIter are not iterating over the same deque.
 */
bool nsDequeIterator::operator<(nsDequeIterator& aIter) {
  return bool(((mIndex<aIter.mIndex) && (&mDeque==&aIter.mDeque)));
}

/**
 * Compare two iterators for equivalence.
 *
 * @param   aIter is the other iterator to be compared to
 * @return  TRUE if EQUAL
 */
bool nsDequeIterator::operator==(nsDequeIterator& aIter) {
  return bool(((mIndex==aIter.mIndex) && (&mDeque==&aIter.mDeque)));
}

/**
 * Compare two iterators for non strict decreasing order.
 *
 * @param   aIter is the other iterator to be compared to
 * @return  TRUE if this object points to the same element, or
 *          an element after the element pointed to by aIter.
 *          FALSE if this and aIter are not iterating over the same deque.
 */
bool nsDequeIterator::operator>=(nsDequeIterator& aIter) {
  return bool(((mIndex>=aIter.mIndex) && (&mDeque==&aIter.mDeque)));
}

/**
 * Pre-increment operator
 *
 * @return  object at post-incremented index
 */
void* nsDequeIterator::operator++() {
  NS_ASSERTION(mIndex<mDeque.mSize,
    "You have reached the end of the Internet."\
    "You have seen everything there is to see. Please go back. Now."
  );
#ifndef TIMELESS_LIGHTWEIGHT
  if (mIndex>=mDeque.mSize) return 0;
#endif
  return mDeque.ObjectAt(++mIndex);
}

/**
 * Post-increment operator
 *
 * @param   param is ignored
 * @return  object at pre-incremented index
 */
void* nsDequeIterator::operator++(int) {
  NS_ASSERTION(mIndex<=mDeque.mSize,
    "You have already reached the end of the Internet."\
    "You have seen everything there is to see. Please go back. Now."
  );
#ifndef TIMELESS_LIGHTWEIGHT
  if (mIndex>mDeque.mSize) return 0;
#endif
  return mDeque.ObjectAt(mIndex++);
}

/**
 * Pre-decrement operator
 *
 * @return  object at pre-decremented index
 */
void* nsDequeIterator::operator--() {
  NS_ASSERTION(mIndex>=0,
    "You have reached the beginning of the Internet."\
    "You have seen everything there is to see. Please go forward. Now."
  );
#ifndef TIMELESS_LIGHTWEIGHT
  if (mIndex<0) return 0;
#endif
  return mDeque.ObjectAt(--mIndex);
}

/**
 * Post-decrement operator
 *
 * @param   param is ignored
 * @return  object at post-decremented index
 */
void* nsDequeIterator::operator--(int) {
  NS_ASSERTION(mIndex>=0,
    "You have already reached the beginning of the Internet."\
    "You have seen everything there is to see. Please go forward. Now."
  );
#ifndef TIMELESS_LIGHTWEIGHT
  if (mIndex<0) return 0;
#endif
  return mDeque.ObjectAt(mIndex--);
}

/**
 * Dereference operator
 * Note that the iterator floats, so you don't need to do:
 * <code>++iter; aDeque.PopFront();</code>
 * Unless you actually want your iterator to jump 2 spaces.
 *
 * Picture: [1 2I 3 4]
 * PopFront()
 * Picture: [2 3I 4]
 * Note that I still happily points to object at the second index
 *
 * @return  object at ith index
 */
void* nsDequeIterator::GetCurrent() {
  NS_ASSERTION(mIndex<mDeque.mSize&&mIndex>=0,"Current is out of bounds");
#ifndef TIMELESS_LIGHTWEIGHT
  if (mIndex>=mDeque.mSize||mIndex<0) return 0;
#endif
  return mDeque.ObjectAt(mIndex);
}

/**
 * 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 nsDequeIterator::ForEach(nsDequeFunctor& aFunctor) const{
  mDeque.ForEach(aFunctor);
}

/**
 * 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* nsDequeIterator::FirstThat(nsDequeFunctor& aFunctor) const{
  return mDeque.FirstThat(aFunctor);
}