#! perl -sw
use 5.010;
use strict;
use Time::HiRes qw[ time ];

my $start = time;

my $size = -s $ARGV[ 0 ];
die("File not a multiple of 4 bytes")
    unless ( $size % 4 ) == 0;

open my $fh, "<:raw", $ARGV[ 0 ]  or die;
my $data;
{
    local $/;
    $data = <$fh>;
}
close $fh;
open $fh, '<', \$data;

my $check_value = 0;
my $buf;

while( read( $fh, $buf, 4 ) ) {

    $check_value ^= unpack 'L', $buf;
    $check_value = ( ( $check_value & 0x7fffffff ) << 1 )
        | ( $check_value >> 31 );
}

say $check_value;

printf "Took: %f seconds\n", time() -$start;

__END__
## Original code
C:\test>767001.pl 767001-small.dat
2779316821
Took: 13.011000 seconds

## Eliminate in loop conditions;
C:\test>767001.pl 767001-small.dat
2779316821
Took: 11.577000 seconds

## Use Ikegami's re-write
C:\test>767001.pl 767001-small.dat
2779316821
Took: 10.453000 seconds

## Use RAM-file
C:\test>767001.pl 767001-small.dat
2779316821
Took: 3.148000 seconds