  ftc_snode_compare( FTC_Node    ftcsnode,
                     FT_Pointer  ftcgquery,
                     FTC_Cache   cache,
                     FT_Bool*    list_changed )
  {
    FTC_SNode   snode  = (FTC_SNode)ftcsnode;
    FTC_GQuery  gquery = (FTC_GQuery)ftcgquery;
    FTC_GNode   gnode  = FTC_GNODE( snode );
    FT_UInt     gindex = gquery->gindex;
    FT_Bool     result;


    if (list_changed)
      *list_changed = FALSE;
    result = FT_BOOL( gnode->family == gquery->family                    &&
                      (FT_UInt)( gindex - gnode->gindex ) < snode->count );
    if ( result )
    {
      /* check if we need to load the glyph bitmap now */
      FTC_SBit  sbit = snode->sbits + ( gindex - gnode->gindex );


      /*
       *  The following code illustrates what to do when you want to
       *  perform operations that may fail within a lookup function.
       *
       *  Here, we want to load a small bitmap on-demand; we thus
       *  need to call the `ftc_snode_load' function which may return
       *  a non-zero error code only when we are out of memory (OOM).
       *
       *  The correct thing to do is to use @FTC_CACHE_TRYLOOP and
       *  @FTC_CACHE_TRYLOOP_END in order to implement a retry loop
       *  that is capable of flushing the cache incrementally when
       *  an OOM errors occur.
       *
       *  However, we need to `lock' the node before this operation to
       *  prevent it from being flushed within the loop.
       *
       *  When we exit the loop, we unlock the node, then check the `error'
       *  variable.  If it is non-zero, this means that the cache was
       *  completely flushed and that no usable memory was found to load
       *  the bitmap.
       *
       *  We then prefer to return a value of 0 (i.e., NO MATCH).  This
       *  ensures that the caller will try to allocate a new node.
       *  This operation consequently _fail_ and the lookup function
       *  returns the appropriate OOM error code.
       *
       *  Note that `buffer == NULL && width == 255' is a hack used to
       *  tag `unavailable' bitmaps in the array.  We should never try
       *  to load these.
       *
       */

      if ( sbit->buffer == NULL && sbit->width == 255 )
      {
        FT_ULong  size;
        FT_Error  error;


        ftcsnode->ref_count++;  /* lock node to prevent flushing */
                                /* in retry loop                 */

        FTC_CACHE_TRYLOOP( cache )
        {
          error = ftc_snode_load( snode, cache->manager, gindex, &size );
        }
        FTC_CACHE_TRYLOOP_END( list_changed );

        ftcsnode->ref_count--;  /* unlock the node */

        if ( error )
          result = 0;
        else
          cache->manager->cur_weight += size;
      }
    }

    return result;
  }

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.