// Decimal representation of Binary data
function binar2dec($a) {
    $s = '';
    if(is_string($a)) $a = str_split($a, 1);
    while($a) {
        $n = 0;
        foreach($a as $i => $m) {
            $m = is_string($m) ? ord($m) : (int)$m;
            $n = ($n << 8) + $m;
            $m = $n % 10;
            $a[$i] = ($n-$m) / 10;
            $n = $m;
        }              
        $s = $n . $s;
        while($a && reset($a) == 0) unset($a[key($a)]);
    }
    return $s;
}

$n = array_fill(0, 26, 0);
$n[0] = 1;

echo binar2dec($n), "\n";

// 1 + 2 + 4 + 8 + ... + 2^63 = 2^64 - 1
echo binar2dec("\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"), "\n";