#! perl -slw
use strict;
use Time::HiRes qw[ time ];

our $N //= 100;

my $start = time;

open INDEX, '<:raw', "$ARGV[ 0 ].idx" or die $!;
my $len = -s( INDEX );
sysread INDEX, my( $idx ), $len;
close INDEX;

sub getRecordN {
    my( $fh, $n ) = @_;
    seek $fh, unpack( 'N', substr $idx, $n * 4, 4 ), 0;
    return scalar <$fh>;
}

scalar <ARGV>;
my @lines; $#lines = $N; $#lines = 0;

for( 1 .. $N ) {
    my $toRead = int rand( length( $idx ) / 4 );
    my $line = getRecordN( \*ARGV, $toRead );
#    push @lines, "$toRead : $offset : ", $line;
}

printf "Ave: %.6f seconds/record\n", ( time() -$start ) / $N;

__END__
c:\test>readIndexedFile -N=1e6 1GB.csv
Ave. 0.000481 seconds/record