Merged changesets r12046-12048 from the trunk (bug fix and test).

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/4.0@12049 280ebfd0-de03-0410-8827-d642c229c3f4

3 files changed, 31 insertions, 7 deletions

diff --git a/src/exp_2.c b/src/exp_2.c
index a9439b8b0..64a9fd286 100644
--- a/src/exp_2.c
+++ b/src/exp_2.c
@@ -198,14 +198,15 @@ mpfr_exp_2 (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
 
       mpfr_sub (r, x, r, MPFR_RNDU);
 
+      while (MPFR_IS_PURE_FP(r) && MPFR_IS_NEG (r))
+        { /* initial approximation n was too large */
+          n--;
+          mpfr_add (r, r, s, MPFR_RNDU);
+        }
+
+      /* if r is 0, we cannot round correctly */
       if (MPFR_LIKELY(MPFR_IS_PURE_FP (r)))
         {
-          while (MPFR_IS_NEG (r))
-            { /* initial approximation n was too large */
-              n--;
-              mpfr_add (r, r, s, MPFR_RNDU);
-            }
-
           /* since there was a cancellation in x - n*log(2), the low error_r
              bits from r are zero and thus non significant, thus we can reduce
              the working precision */
diff --git a/src/subnormal.c b/src/subnormal.c
index 0a135aa9f..1b75ce8b7 100644
--- a/src/subnormal.c
+++ b/src/subnormal.c
@@ -145,7 +145,10 @@ mpfr_subnormalize (mpfr_ptr y, int old_inexact, mpfr_rnd_t rnd)
                   if (SAME_SIGN (inexact, MPFR_INT_SIGN (y)))
                     mpfr_nexttozero (dest);
                   else  /* subnormal range, thus no overflow */
-                    mpfr_nexttoinf (dest);
+                    {
+                      mpfr_nexttoinf (dest);
+                      MPFR_ASSERTD(!MPFR_IS_INF (dest));
+                    }
                   inexact = -inexact;
                 }
             }
diff --git a/tests/texp.c b/tests/texp.c
index 1d002bd2e..b27e51068 100644
--- a/tests/texp.c
+++ b/tests/texp.c
@@ -972,6 +972,24 @@ underflow (void)
     }
 }
 
+/* bug found with GMP_CHECK_RANDOMIZE=1514290185 */
+static void
+bug20171223 (void)
+{
+  mpfr_t x, y;
+  int inex;
+
+  mpfr_init2 (x, 372);
+  mpfr_init2 (y, 2);
+  mpfr_set_str (x, "-6.9314716128384587678466323621915206417385796077947874471662159283492445979241549847386366371775938082803907383582e-01", 10, MPFR_RNDN);
+  /* exp(x) = 0.500000009638..., should be rounded to 0.5 */
+  inex = mpfr_exp (y, x, MPFR_RNDD);
+  MPFR_ASSERTN(mpfr_cmp_ui_2exp (y, 1, -1) == 0);
+  MPFR_ASSERTN(inex < 0);
+  mpfr_clear (x);
+  mpfr_clear (y);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -980,6 +998,8 @@ main (int argc, char *argv[])
   if (argc > 1)
     check_large ();
 
+  bug20171223 ();
+
   check_inexact ();
   check_special ();