void CLASS layer_thumb()
{
  unsigned i;
  int c;
  char *thumb, map[][4] = { "012","102" };

  colors = thumb_misc >> 5 & 7;
  thumb_length = thumb_width*thumb_height;
  thumb = (char *) calloc (colors, thumb_length);
  merror (thumb, "layer_thumb()");
  fprintf (ofp, "P%d\n%d %d\n255\n",
	5 + (colors >> 1), thumb_width, thumb_height);
  fread (thumb, thumb_length, colors, ifp);
  for (i=0; i < thumb_length; i++)
    FORCC putc (thumb[i+thumb_length*(map[thumb_misc >> 8][c]-'0')], ofp);
  free (thumb);
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.