use constant NAND_PAGE_SIZE => 16384;  # or whatever...
{
  open IMAGE, '<', $image_file_name or die "$image_file_name: $!";
  local $/ = \NAND_PAGE_SIZE;
  while (<IMAGE>) {
    my $ppn = (tell IMAGE) / NAND_PAGE_SIZE;
    my $lpn = get_LPN($_);
    $PPN[$ppn] = { LPN => $lpn, XPPN => [ get_XPPNs($_) ] };
    push @{$LPN[$lpn]}, $ppn;
  }
  close IMAGE;
}