#!/usr/bin/perl
$| = 1;
open($FILE_A, "< $_") if($_ = shift);
open($FILE_B, "< $_") if($_ = shift);
while(!$FILE_A)
{
    print "file A: ";
    chomp($_ = <>);
    open($FILE_A, "< $_");
}
while(!$FILE_B)
{
    print "file B: ";
    chomp($_ = <>);
    open($FILE_B, "< $_");
}
while(!eof($FILE_A) && !eof($FILE_B))
{
    $short_a = unpack("s*", getc($FILE_A) . getc($FILE_A));
    $short_b = unpack("s*", getc($FILE_B) . getc($FILE_B));
    if($short_a > $short_b)
    {
        $diff = $short_a - $short_b;
        $sign = "+";
    }
    if($short_a < $short_b)
    {
        $diff = $short_b - $short_a;
        $sign = "-";
    }
    if($short_a == $short_b)
    {
        $diff = 0;
        $sign = " ";
    }
    $sum += abs($diff);
    $count += 2;
    printf("%10dk\r", $count / 1024) if($count % 1024 == 0);
#    print "\n$sum\n" if($count % 10240 == 0);
}
print "Average difference: " . ($sum / $count) . "\n";