[tests/] Detect double rounding for a mpfr_t output.

git-svn-id: svn://scm.gforge.inria.fr/svn/mpc/branches/benchs_tests@1352 211d60ee-9f03-0410-a15a-8952a2c7a4e4

1 files changed, 53 insertions, 1 deletions

diff --git a/tests/tgeneric.tpl b/tests/tgeneric.tpl
index 120dea3..ae503fb 100644
--- a/tests/tgeneric.tpl
+++ b/tests/tgeneric.tpl
@@ -300,6 +300,37 @@ random_params (mpc_fun_param_t *params,
 /* return 1 if double rounding occurs;
    return 0 otherwise */
 static int
+double_rounding_mpfr (mpfr_ptr lowprec, mpfr_ptr hiprec, int inex,
+                      mpfr_rnd_t rnd)
+{
+  mpfr_exp_t hiprec_err;
+  mpfr_rnd_t lowprec_rnd = rnd;
+  mpfr_prec_t lowprec_prec = mpfr_get_prec (lowprec);
+
+  /* hiprec error is bounded by one ulp */
+  hiprec_err = mpfr_get_prec (hiprec) - 1;
+
+  if (rnd == MPFR_RNDN)
+    /* when rounding to nearest, use the trick for determining the
+       correct ternary value which is described in MPFR
+       documentation */
+    {
+      hiprec_err++; /* error is bounded by one half-ulp */
+      lowprec_rnd = MPFR_RNDZ;
+      lowprec_prec++;
+    }
+
+  return (mpfr_nan_p (hiprec)
+          || mpfr_zero_p (hiprec)
+          || mpfr_inf_p (hiprec)
+          || inex == 0
+          || mpfr_can_round (hiprec, hiprec_err, rnd,
+                             lowprec_rnd, lowprec_prec));
+}
+
+/* return 1 if double rounding occurs;
+   return 0 otherwise */
+static int
 double_rounding_mpc (mpc_ptr lowprec, mpc_ptr hiprec, int inex, mpc_rnd_t rnd)
 {
   /* reference value in high precision */
@@ -387,7 +418,28 @@ double_rounding (mpc_fun_param_t *params)
       }
     else if (params->T[out] == MPFR)
       {
-        /* TODO */
+        MPC_ASSERT (params->T[0] == MPFR_INEX);
+        MPC_ASSERT (params->T[offset] == MPFR_INEX);
+        MPC_ASSERT (params->T[out + offset] == MPFR);
+        MPC_ASSERT (params->T[rnd_index] == MPFR_RND);
+
+        if (double_rounding_mpfr (params->P[out + offset].mpfr_data.mpfr,
+                                  params->P[out].mpfr,
+                                  params->P[0].mpfr_inex,
+                                  params->P[rnd_index].mpfr_rnd))
+          /* the hight-precision value and the exact value round to the same
+             low-precision value */
+          {
+            int inex;
+            inex = mpfr_set (params->P[out + offset].mpfr_data.mpfr,
+                             params->P[out].mpfr,
+                             params->P[rnd_index].mpfr_rnd);
+            params->P[out + offset].mpfr_data.known_sign = -1;
+            params->P[offset].mpfr_inex = inex;
+          }
+        else
+          /* double rounding occurs */
+          return 1;
       }
   }
   return 0;