my @offsets;

sub Set_line (\*\$\$) {
  my $fh_r=shift @_;
  my $cur_r=shift @_;
  my $row_r=shift @_;

  if ($offsets[$$row_r]){
    # We know where the row is, so just go there.
    seek($ffh_r, $offsets[$$row_r], 0);
  } elsif ($$cur_r>$$row_r) {
    # We don't know where it is, so we should start at the end of the area that we've indexed
    seek ($$fh_r, $offsets[-1],0);
    $$cur_r= scalar $offsets;
  }
  while (!(($$cur_r)==$$row_r) && $_ ne "") {
    $_=readline($fh_r);
    $$cur_r++;
    $offset[$$cur_r] = tell($$fh_r);
  }
  return;
}