That looks at lot like the lines 153-162 from here (direct link here):

153    // read number
154    function readNumber(){
155      $num = fread($this->buffer, 8);
156      $r = "";
157      for($byte = 7 ; $byte >= 0 ; $byte--) { // reverse the bytes
158        $r .= $num[$byte];
159      }
160      $ret = unpack("dnum",$r);
161      return $ret['num'];
162    }
[download]

And I believe that's PHP, not Perl. I'm thankful for the suggestion although still looking for the Perl equivalent of the above.