function conv_case($charset, $string, $case) {
        if ($GLOBALS['TYPO3_CONF_VARS']['SYS']['t3lib_cs_utils'] == 'mbstring') {
            if ($case == 'toLower') {
                $string = mb_strtolower($string, $charset);
            } else {
                $string = mb_strtoupper($string, $charset);
            }
        } elseif ($charset == 'utf-8') {
            $string = $this->utf8_char_mapping($string, 'case', $case);
        } elseif (isset($this->eucBasedSets[$charset])) {
            $string = $this->euc_char_mapping($string, $charset, 'case', $case);
        } else {
                // treat everything else as single-byte encoding
            $string = $this->sb_char_mapping($string, $charset, 'case', $case);
        }

        return $string;
    }