OpenSSL::BN#to_s

static VALUE
ossl_bn_to_s(int argc, VALUE *argv, VALUE self)
{
    BIGNUM *bn;
    VALUE str, bs;
    int base = 10, len;
    char *buf;

    if (rb_scan_args(argc, argv, "01", &bs) == 1) {
        base = NUM2INT(bs);
    }
    GetBN(self, bn);
    switch (base) {
    case 0:
        len = BN_bn2mpi(bn, NULL);
        str = rb_str_new(0, len);
        if (BN_bn2mpi(bn, (unsigned char *)RSTRING_PTR(str)) != len)
            ossl_raise(eBNError, NULL);
        break;
    case 2:
        len = BN_num_bytes(bn);
        str = rb_str_new(0, len);
        if (BN_bn2bin(bn, (unsigned char *)RSTRING_PTR(str)) != len)
            ossl_raise(eBNError, NULL);
        break;
    case 10:
        if (!(buf = BN_bn2dec(bn))) ossl_raise(eBNError, NULL);
        str = ossl_buf2str(buf, rb_long2int(strlen(buf)));
        break;
    case 16:
        if (!(buf = BN_bn2hex(bn))) ossl_raise(eBNError, NULL);
        str = ossl_buf2str(buf, rb_long2int(strlen(buf)));
        break;
    default:
        ossl_raise(rb_eArgError, "invalid radix %d", base);
    }

    return str;
}