UBF support fixed in mpfr_sub1 (src/sub1.c):

  * underflow detection (which could affect mpfr_{fma,fms,fmma,fmms});
  * MPFR_RNDF (mpfr_set4, which doesn't support UBF, could be called).

In the tests directory:
  * tfma.c: disabled some tests on MPFR_RNDF (since the results are
    not fully specified, the tests are heuristics only and depend on
    a particular implementation, which has changed for the bug fix).
  * tfmma.c: added a testcase showing how the above bug could affect
    mpfr_fmms.
  * tsub.c: added tests on UBF (thus using internals).

(merged changesets r13703,13796-13807,13810-13815,13818,13821 from the
trunk)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/4.0@13837 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/tfmma.c b/tests/tfmma.c
index a4243cca2..34567bd5a 100644
--- a/tests/tfmma.c
+++ b/tests/tfmma.c
@@ -577,6 +577,26 @@ bug20200206 (void)
   mpfr_set_emin (emin);
 }
 
+/* check for integer overflow (see bug fixed in r13798) */
+static void
+extreme_underflow (void)
+{
+  mpfr_t x, y, z;
+  mpfr_exp_t emin = mpfr_get_emin ();
+
+  set_emin (MPFR_EMIN_MIN);
+  mpfr_inits2 (64, x, y, z, (mpfr_ptr) 0);
+  mpfr_set_ui_2exp (x, 1, MPFR_EMIN_MIN - 1, MPFR_RNDN);
+  mpfr_set (y, x, MPFR_RNDN);
+  mpfr_nextabove (x);
+  mpfr_clear_flags ();
+  mpfr_fmms (z, x, x, y, y, MPFR_RNDN);
+  MPFR_ASSERTN (__gmpfr_flags == (MPFR_FLAGS_UNDERFLOW | MPFR_FLAGS_INEXACT));
+  MPFR_ASSERTN (MPFR_IS_ZERO (z) && MPFR_IS_POS (z));
+  mpfr_clears (x, y, z, (mpfr_ptr) 0);
+  set_emin (emin);
+}
+
 /* Test double-rounding cases in mpfr_set_1_2, which is called when
    all the precisions are the same. With set.c before r13347, this
    triggers errors for neg=0. */
@@ -655,6 +675,7 @@ main (int argc, char *argv[])
   half_plus_half ();
   bug20170405 ();
   double_rounding ();
+  extreme_underflow ();
 
   tests_end_mpfr ();
   return 0;