no installation warnings for new or old MPFR

.travis.yml

@@ -1,5 +1,4 @@
 sudo: required
-dist: trusty
 language: r
 r_binary_packages:
     - Rcpp

cran-comments.md

@@ -1,6 +1,6 @@
 ## Test environments
 * Linux
-  - R 3.2.3
+  - R 3.6.1
   - apt packages: build-essential, libmpfr-dev, libblas-dev, liblapack-dev
 * Windows
   - R 3.4.1, R 3.5.2
@@ -9,7 +9,7 @@
   - R 3.5.3
   - brew packages: mpfr
 * Travis-CI
-  - R 3.5.2 (Linux)
+  - R 3.5.2, libmpfr-dev_3.1.2-1 (Linux)
   - R 3.5.3 (OS X)
 
 ## R CMD check results

src/mpreal.h

@@ -2198,8 +2198,11 @@ inline const mpreal sqrt(const int v, mp_rnd_t rnd_mode)
 inline const mpreal root(const mpreal& x, unsigned long int k, mp_rnd_t r = mpreal::get_default_rnd())
 {
     mpreal y(0, mpfr_get_prec(x.mpfr_srcptr()));
-    //mpfr_root(y.mpfr_ptr(), x.mpfr_srcptr(), k, r);
+#if MPFR_VERSION_MAJOR >= 4
     mpfr_rootn_ui(y.mpfr_ptr(), x.mpfr_ptr(), k, r);
+#else
+    mpfr_root(y.mpfr_ptr(), x.mpfr_srcptr(), k, r);
+#endif
     return y;
 }
 
@@ -2644,7 +2647,11 @@ inline const mpreal random(unsigned int seed = 0)
 inline const mpreal grandom (gmp_randstate_t& state, mp_rnd_t rnd_mode = mpreal::get_default_rnd())
 {
     mpreal x;
+#if MPFR_VERSION_MAJOR >= 4
     mpfr_nrandom(x.mpfr_ptr(), state, rnd_mode);
+#else
+    mpfr_grandom(x.mpfr_ptr(), NULL, state, rnd_mode);
+#endif
     return x;
 }