[src/fma.c] added comments

[tests/tfma.c] added a test (currently failing)


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@12393 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/tfma.c b/tests/tfma.c
index f3a3b30e7..b8918a192 100644
--- a/tests/tfma.c
+++ b/tests/tfma.c
@@ -196,6 +196,29 @@ test_overflow2 (void)
 }
 
 static void
+test_overflow3 (void)
+{
+  mpfr_t x, y, z, r;
+  int inex;
+  mpfr_prec_t p = 8;
+
+  mpfr_inits2 (p, x, y, z, (mpfr_ptr) 0);
+  mpfr_init2 (r, 2 * p);
+  mpfr_set_ui_2exp (x, 1, mpfr_get_emax () - 1, MPFR_RNDN);
+  mpfr_set_ui (y, 2, MPFR_RNDN);       /* y = 2 */
+  mpfr_set_si_2exp (z, -1, mpfr_get_emax () - 2*p - 2, MPFR_RNDN);
+  mpfr_nextabove (z);
+  mpfr_clear_flags ();
+  /* We have x*y = 2^emax and z = -2^(emax-2p-2)*(1-2^(-p)) thus
+     x*y+z = 2^emax - 2^(emax-2p-2) + 2^(emax-3p-2) should overflow,
+     since it is closest from 2^emax than from 2^emax - 2^(emax-2p). */
+  inex = mpfr_fma (r, x, y, z, MPFR_RNDN);
+  MPFR_ASSERTN(inex > 0);
+  MPFR_ASSERTN(mpfr_inf_p (r) && mpfr_sgn (r) > 0);
+  mpfr_clears (x, y, z, r, (mpfr_ptr) 0);
+}
+
+static void
 test_underflow1 (void)
 {
   mpfr_t x, y, z, r;
@@ -833,6 +856,7 @@ main (int argc, char *argv[])
   set_emax (MPFR_EMAX_MAX);
   test_overflow1 ();
   test_overflow2 ();
+  test_overflow3 ();
   test_underflow1 ();
   test_underflow2 ();
   test_underflow3 (2);