Function _lf_dynarray_lvalue

mysys/lf_dynarray.c:98–145

Returns a valid lvalue pointer to the element number 'idx'. Allocates memory if necessary. */

  Allocates memory if necessary.
*/
void *_lf_dynarray_lvalue(LF_DYNARRAY *array, uint idx)
{
  void * ptr, * volatile * ptr_ptr= 0;
  int i;

  for (i= LF_DYNARRAY_LEVELS-1; idx < dynarray_idxes_in_prev_levels[i]; i--)
    /* no-op */;
  ptr_ptr= &array->level[i];
  idx-= dynarray_idxes_in_prev_levels[i];
  for (; i > 0; i--)
  {
    if (!(ptr= *ptr_ptr))
    {
      void *alloc= my_malloc(LF_DYNARRAY_LEVEL_LENGTH * sizeof(void *),
                             MYF(MY_WME|MY_ZEROFILL));
      if (unlikely(!alloc))
        return(NULL);
      if (my_atomic_casptr(ptr_ptr, &ptr, alloc))
        ptr= alloc;
      else
        my_free(alloc);
    }
    ptr_ptr= ((void **)ptr) + idx / dynarray_idxes_in_prev_level[i];
    idx%= dynarray_idxes_in_prev_level[i];
  }
  if (!(ptr= *ptr_ptr))
  {
    uchar *alloc, *data;
    alloc= my_malloc(LF_DYNARRAY_LEVEL_LENGTH * array->size_of_element +
                     MY_MAX(array->size_of_element, sizeof(void *)),
                     MYF(MY_WME|MY_ZEROFILL));
    if (unlikely(!alloc))
      return(NULL);
    /* reserve the space for free() address */
    data= alloc + sizeof(void *);
    { /* alignment */
      intptr mod= ((intptr)data) % array->size_of_element;
      if (mod)
        data+= array->size_of_element - mod;
    }
    ((void **)data)[-1]= alloc; /* free() will need the original pointer */
    if (my_atomic_casptr(ptr_ptr, &ptr, data))
      ptr= data;
    else
      my_free(alloc);
  }
  return ((uchar*)ptr) + array->size_of_element * idx;
}

/*
  Returns a pointer to the element number 'idx'