Function expat_realloc

Utilities/cmexpat/lib/xmlparse.c:940–1012

void *
#  else
static void *
#  endif
expat_realloc(XML_Parser parser, void *ptr, size_t size, int sourceLine) {
  assert(parser != NULL);

  if (ptr == NULL) {
    return expat_malloc(parser, size, sourceLine);
  }

  if (size == 0) {
    expat_free(parser, ptr, sourceLine);
    return NULL;
  }

  const XML_Parser rootParser = getRootParserOf(parser, NULL);
  assert(rootParser->m_parentParser == NULL);

  // Extract original size (to the eyes of the caller) and the original
  // pointer returned by malloc/realloc
  void *mallocedPtr = (char *)ptr - EXPAT_MALLOC_PADDING - sizeof(size_t);
  const size_t prevSize = *(size_t *)mallocedPtr;

  // Classify upcoming change
  const bool isIncrease = (size > prevSize);
  const size_t absDiff
      = (size > prevSize) ? (size - prevSize) : (prevSize - size);

  // Ask for permission from accounting
  if (isIncrease) {
    if (! expat_heap_increase_tolerable(rootParser, absDiff, sourceLine)) {
      return NULL; // i.e. signal violation as out-of-memory
    }
  }

  // NOTE: Integer overflow detection has already been done for us
  //       by expat_heap_increase_tolerable(..) above
  assert(SIZE_MAX - sizeof(size_t) - EXPAT_MALLOC_PADDING >= size);

  // Actually allocate
  mallocedPtr = parser->m_mem.realloc_fcn(
      mallocedPtr, sizeof(size_t) + EXPAT_MALLOC_PADDING + size);

  if (mallocedPtr == NULL) {
    return NULL;
  }

  // Update accounting
  if (isIncrease) {
    assert((XmlBigCount)-1 - rootParser->m_alloc_tracker.bytesAllocated
           >= absDiff);
    rootParser->m_alloc_tracker.bytesAllocated += absDiff;
  } else { // i.e. decrease
    assert(rootParser->m_alloc_tracker.bytesAllocated >= absDiff);
    rootParser->m_alloc_tracker.bytesAllocated -= absDiff;
  }

  // Report as needed
  if (rootParser->m_alloc_tracker.debugLevel >= 2) {