#! perl -sw
use 5.010;
use strict;
use Time::HiRes qw[ time ];
use constant BUFSIZ => 64 * 1024;

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 $check_value = 0;
my $buf;

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

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

say $check_value;

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

__END__
## Process 4K chunks
C:\test>767001-buk 767001-small.dat
2779316821
Took: 1.771000 seconds

## Process 16K chunks
C:\test>767001-buk 767001-small.dat
2779316821
Took: 1.750000 seconds

## Process 64K chunks
C:\test>767001-buk 767001-small.dat
2779316821
Took: 1.775000 seconds

...
## Process 256K chunks
C:\test>767001-buk 767001-small.dat
2779316821
Took: 1.804000 seconds