re.c:245
int
rb_reg_mbclen2(c, re)
    unsigned int c;
    VALUE re;
{
    int len;

    if (!FL_TEST(re, KCODE_FIXED))
	return mbclen(c);
    kcode_set_option(re);
    len = mbclen(c);
    kcode_reset_option();
    return len;
}
