open O, '+<:raw', '1GBx8.bin' or die $!;;

seek O, 0, 0; $t=time; seek O, $_*1000, 0 for 0 .. 8589934; print time-$t;;
7.61572408676147

seek O, 0, 0; $t=time; seek O, 1000, 1 for 0 .. 8589934; print time-$t;;
11.6447620391846

seek O, 0, 2; $t=time; seek O, -1000, 1 for 0 .. 8589934; print time-$t;;
11.6476919651031

seek O, 0, 2; $t=time; seek O, $_*-1000, 2 for 0 .. 8589934; print time-$t;;
23.074695110321