Compact, human-editable serialization

Somewhere around here I asked about human-readable serialization and there was no solution that fitted my needs. So I wrote my own serialize/deserialize pair. The decode function is different from the one I posted here before. This function, in my opinion, is written very efficiently, but it's still about 10-50 times slower than serialize. I guess it's not too bad, because I compete with pure C++ code, but I would still appreciate any suggestion for performance tune-up. PS: If someone would write the same functions in C, they wold probably be faster than PHP's de/serialize. And they provide output that is much more compact. And it's human-editable. PHP developers, if you read this, think about it. --- function encode($var) { if (is_array($var)) {

       $code = '(';
       foreach ($var as $key => $value) {
           $code .= encode($key).'='.encode($value).',';
       }
       $code = chop($code, ','); //remove unnecessary coma
       $code .= ')';
       return $code;

} else {

       if (is_string($var)) { //this also catches string with numbers inside
           if (strpos($var, "'") !== FALSE) {
               $var = str_replace("'", "''", $var);
           }
           return "'".$var."'";
       } elseif (is_numeric($var)) {
           return $var;
       } elseif (is_bool($var)) {
           return ($var ? 'T' : 'F');
       } else {
           return 'N';
       }

} } function decode($str) {

    preg_match_all('/"(.*?)"/s', $str, $matches, PREG_PATTERN_ORDER);
    $dStack = $matches[1];
    $str = preg_replace('/".*?"/s', 'D', $str);

    preg_match_all("/'(.*?)'/s", $str, $matches, PREG_PATTERN_ORDER);
    $sStack = $matches[1];
    $str = preg_replace("/'.*?'/s", "S", $str);

    if (preg_match('/[\'"]/', $string)) {
        user_error("Unpaired quotes", E_USER_WARNING);
        return;
    }

    $str = preg_replace('/\s/', '', $str);
    $str = preg_replace('/,\)/', ')', $str);

    preg_match_all('/([^TFNDS=,\(\)]+)/i', $str, $matches, PREG_PATTERN_ORDER);
    $xStack = $matches[1];
    $str = preg_replace('/[^TFNDS=,\(\)]+/i', 'X', $str);

    $heap = array();
    $ptr = strlen($str) - 1;

    while ($ptr != 0) {
        switch ($str{$ptr}) {
            case 'D':
            $string = array_pop($sStack);
            while ($str{$ptr - 1} == 'D') {
                $string = array_pop($dStack).'"'.$string;
                $str{$ptr} = '_';
                --$ptr;
            }
            $str{$ptr} = '$';
            $heap[$subPtr] = $string;
            break;

            case 'S':
            $string = array_pop($sStack);
            while ($str{$ptr - 1} == 'S') {
                $string = array_pop($sStack)."'".$string;
                $str{$ptr} = '_';
                --$ptr;
            }
            $str{$ptr} = '$';
            $heap[$ptr] = $string;
            break;

            case 'T':
            $heap[$ptr] = TRUE;
            $str{$ptr} = '$';
            break;

            case 'F':
            $heap[$ptr] = FALSE;
            $str{$ptr} = '$';
            break;

            case 'N':
            $heap[$ptr] = NULL;
            $str{$ptr} = '$';
            break;

            case 'X':
            $number = array_pop($xStack);
            $str{$ptr} = '$';
            if (is_numeric($number)) {
                $heap[$ptr] = $number + 0;
            } else {
                user_error('Invalid character sequence in array ['.($ptr - 1).']', E_USER_WARNING);
                return;
            }
            break;
        } //braces, commas and equal signs are ignored
        --$ptr;
    }

    while (($aStart = strrpos($str, '(')) !== FALSE) {
        $aEnd = strpos($str, ')', $aStart);
        if ($aEnd === FALSE) {
            user_error("Array beginning at [$aStart] is not closed", E_USER_WARNING);
            return;
        }

        $ptr = $aStart + 1;
        if ($str{$ptr} == ',' || $str{$ptr} == '=') {
            user_error("Invalid array entry [$ptr]", E_USER_WARNING);
            return;
        }

        $str{$aEnd} = ','; //comma serves as a trigger, so array should end with one

        $aStack = array();
        while ($ptr < $aEnd) {
            switch ($str{$ptr}) {
                case '=':
                $str{$ptr} = '_';
                $keyPtr = $ptr - 1;
                while ($str{$keyPtr} != '$') {
                    if ($str{$keyPtr} != '_') {
                        user_error("Invalid character sequence in array [$keyPtr]", E_USER_WARNING);
                        return;
                    }
                    $str{$keyPtr} = '_';
                    --$keyPtr;
                }
                $str{$keyPtr} = '_';
                $valPtr = $ptr + 1;
                if ($str{$valPtr} != '$') {
                    user_error("Invalid character sequence in array [$keyPtr]", E_USER_WARNING);
                    return;
                }
                $str{$valPtr} = '_';
                $aStack[$heap[$keyPtr]]= $heap[$valPtr];
                $commaPtr = $valPtr + 1;
                while ($str{$commaPtr} != ',') {
                    if ($str{$commaPtr} != '_') {
                        user_error("Invalid character sequence in array [$commaPtr]", E_USER_WARNING);
                        return;
                    }
                    ++$commaPtr;
                }
                $str{$commaPtr} = '_';
                break;

                case ',':
                $str{$ptr} = '_';
                $valPtr = $ptr - 1;
                while ($str{$valPtr} != '$') {
                    if ($str{$valPtr} != '_') {
                        user_error("Invalid character sequence in array [$valPtr]", E_USER_WARNING);
                        return;
                    }
                    $str{$valPtr} = '_';
                    --$valPtr;
                }
                $str{$valPtr} = '_';
                $aStack[]= $heap[$valPtr];
                break;
            }
            ++$ptr;
        }

        $str{$aStart} = '$'; //array is now reduced to a single variable

        $heap[$aStart] = $aStack;
    }

    return $heap[0];

}