SV * Rmpfr_out_str(SV * p, SV * base, SV * dig, SV * round) {
     if(SvIV(base) < 2 || SvIV(base) > 36) croak("2nd argument supplied to Rmpfr_out_str is out of allowable range (must be between 2 and 36 inclusive)");
     return newSVuv(mpfr_out_str(NULL, SvUV(base), SvUV(dig), *(INT2PTR(mpfr_t *, SvIV(SvRV(p)))), SvUV(round)));
}