Judging by the linked-to code, the hash is just summing the ASCII values of each byte. Translating this to fiarly idiomatic Perl, I come up with the following:

use strict;
use warnings;
use Fcntl ':seek';

use constant CHUNK => 65536;

sub calc {
    my $file  = shift or die "no filename given\n";
    my $hash  = -s $file;
    my $chunk = CHUNK;

    $hash < $chunk and die "$file is too small ($hash bytes < $chunk)\
+n";

    open my $in, '<', $file or die "Cannot open $file for input: $!\n"
+;
    local $/ = \$chunk;

    $hash += ord($_) for split //, readline($in);
    seek($in, SEEK_END, -$chunk);
    $hash += ord($_) for split //, readline($in);

    close $in;
    return sprintf '%016x', $hash;
}

print calc($_), "\t$_\n" for @ARGV;
[download]

...but, as GrandFather points out, without a test file and expected results, it's hard to know if there are any bugs in this.

update: I see you've added a test case. And I see that it's actually summing 32-bit values. The following code reflects that fact.

use strict;
use warnings;
use Fcntl ':seek';

use constant CHUNK => 65536;

sub calc {
    my $file  = shift or die "no filename given\n";
    my $hash  = -s $file;
    my $chunk = CHUNK;

    $hash < $chunk and die "$file is too small ($hash bytes < $chunk)\
+n";

    open my $in, '<', $file or die "Cannot open $file for input: $!\n"
+;
    local $/ = \$chunk;

    $hash += $_ for unpack 'N*' , readline($in);
    seek($in, SEEK_END, -$chunk);
    $hash += $_ for unpack 'N*' , readline($in);

    close $in;
    return sprintf '%016x', $hash;
}

my $test = 'test.deleteme';
open my $out, '>', $test;
print $out ' ' x (65536*4);
close $out;

print calc($test), $/;
unlink $test;
[download]

Hmm, but that doesn't match the test results. Back to the drawing board.

2nd update: Got it! It's summing quads, not longs, and clamping on overflow.

I had to use bigint, which is sub-optimal in that it gets the correct results at the cost of vastly increased execution time. Still, it does the job, and on a 64-bit CPU you should be able to remove the 'use bigint' and it will work just the same, and much, much faster.

use strict;
use warnings;
use Fcntl ':seek';
use bigint;

use constant CHUNK => 65536;

sub calc {
    my $file  = shift or die "no filename given\n";
    my $hash  = -s $file;
    my $chunk = CHUNK;

    $hash < $chunk and die "$file is too small ($hash bytes < $chunk)\
+n";

    open my $in, '<', $file or die "Cannot open $file for input: $!\n"
+;
    local $/ = \$chunk;

    for my $quad (unpack 'q*' , readline($in)) {
        $hash += $quad;
        $hash &= 2 ** 64 - 1;
    }
    seek($in, SEEK_END, -$chunk);
    for my $quad (unpack 'q*' , readline($in)) {
        $hash += $quad;
        $hash &= 2 ** 64 - 1;
    }

    close $in;
    return sprintf '%016x', $hash;
}

open my $out, '>', 'test.deleteme';
print $out ' ' x (65536*4);
close $out;

print calc('test.deleteme'), $/;
[download]

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