php 数据脱敏显示

/**
 * 数据脱敏
 * @param $string 需要脱敏值
 * @param int $start 开始
 * @param int $length 结束
 * @param string $re 脱敏替代符号
 * @return bool|string
 * 例子:
 * dataDesensitization('13126989876', 3, 4); //131****9876
 * dataDesensitization('张三四', 0, -1); //**四
 */
function dataDesensitization($string, $start = , $length = , $re = '*')
{
    if (empty($string)){
        return false;
    }
    $strarr = array();
    $mb_strlen = mb_strlen($string);
    while ($mb_strlen) {//循环把字符串变为数组
        $strarr[] = mb_substr($string, , , 'utf8');
        $string = mb_substr($string, , $mb_strlen, 'utf8');
        $mb_strlen = mb_strlen($string);
    }
    $strlen = count($strarr);
    $begin = $start >=  ? $start : ($strlen - abs($start));
    $end = $last = $strlen - ;
    if ($length > ) {
        $end = $begin + $length - ;
    } elseif ($length < ) {
        $end -= abs($length);
    }
    for ($i = $begin; $i <= $end; $i++) {
        $strarr[$i] = $re;
    }
    if ($begin >= $end || $begin >= $last || $end > $last) return false;
    return implode('', $strarr);
}