void overload_add_eq(pTHX_ SV * a, SV * b, SV * third) {
     PERL_UNUSED_ARG(third); /* UPDATE: This line can be removed as irrelevant */
     mpz_add_ui(*(INT2PTR(mpz_t *, SvIVX(SvRV(a)))), *(INT2PTR(mpz_t *, SvIVX(SvRV(a)))), SvUV(b));
}