String::getBinarySubstring

static function getBinarySubstring($str, $start)
{
	if(function_exists('mb_substr'))
	{
		$length = (func_num_args() > 2? func_get_arg(2) : self::getBinaryLength($str));
		return mb_substr($str, $start, $length, 'latin1');
	}
	if(func_num_args() > 2)
	{
		return substr($str, $start, func_get_arg(2));
	}
	return substr($str, $start);
}