Underflow semantics changed (not tested).

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1910 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 9 insertions, 2 deletions

diff --git a/mul_2si.c b/mul_2si.c
index 25066e0a2..cdc522425 100644
--- a/mul_2si.c
+++ b/mul_2si.c
@@ -1,6 +1,6 @@
 /* mpfr_mul_2si -- multiply a floating-point number by a power of two
 
-Copyright 1999, 2001 Free Software Foundation, Inc.
+Copyright 1999, 2001, 2002 Free Software Foundation, Inc.
 
 This file is part of the MPFR Library.
 
@@ -39,7 +39,14 @@ mpfr_mul_2si (mpfr_ptr y, mpfr_srcptr x, long int n, mp_rnd_t rnd_mode)
 
       if (n < 0 && (__mpfr_emin > MPFR_EMAX_MAX + n ||
                     MPFR_EXP(y) < __mpfr_emin - n))
-        return mpfr_set_underflow (y, rnd_mode, MPFR_SIGN(y));
+        {
+          if (rnd_mode == GMP_RNDN &&
+              (__mpfr_emin > MPFR_EMAX_MAX + (n + 1) ||
+               MPFR_EXP(y) < __mpfr_emin - (n + 1) ||
+               mpfr_powerof2_raw (y)))
+            rnd_mode = GMP_RNDZ;
+          return mpfr_set_underflow (y, rnd_mode, MPFR_SIGN(y));
+        }
 
       MPFR_EXP(y) += n;
     }