[src/div.c] fixed bug in mpfr_div2_approx()

[tests/tdiv.c] added non-regression test
[tests/ttan.c] added test triggering bug in mpfr_div2_approx()


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@12002 280ebfd0-de03-0410-8827-d642c229c3f4

3 files changed, 39 insertions, 1 deletions

diff --git a/src/div.c b/src/div.c
index 3ef62b6d5..7d208621f 100644
--- a/src/div.c
+++ b/src/div.c
@@ -71,7 +71,8 @@ mpfr_div2_approx (mpfr_limb_ptr Q1, mpfr_limb_ptr Q0,
 
   /* we ignore yy below, but first increment r0, to ensure we get a lower
      approximation of the remainder */
-  r0 += (yy != 0);
+  r0 += yy != 0;
+  r1 += r0 == 0 && yy != 0;
   r0 = u0 - r0;
   r1 = u1 - r1 - (r0 > u0);
 
diff --git a/tests/tdiv.c b/tests/tdiv.c
index 077347e66..5b0bb04e6 100644
--- a/tests/tdiv.c
+++ b/tests/tdiv.c
@@ -1479,11 +1479,28 @@ test_mpfr_div2_approx (unsigned long n)
 }
 #endif
 
+/* bug found in ttan with GMP_CHECK_RANDOMIZE=1514257254 */
+static void
+bug20171218 (void)
+{
+  mpfr_t s, c;
+  mpfr_init2 (s, 124);
+  mpfr_init2 (c, 124);
+  mpfr_set_str_binary (s, "-0.1110000111100001111000011110000111100001111000011110000111100001111000011110000111100001111000011110000111100001111000011110E0");
+  mpfr_set_str_binary (c, "0.1111000011110000111100001111000011110000111100001111000011110000111100001111000011110000111100001111000011110000111100001111E-1");
+  mpfr_div (c, s, c, MPFR_RNDN);
+  mpfr_set_str_binary (s, "-1.111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000");
+  MPFR_ASSERTN(mpfr_equal_p (c, s));
+  mpfr_clear (s);
+  mpfr_clear (c);
+}
+
 int
 main (int argc, char *argv[])
 {
   tests_start_mpfr ();
 
+  bug20171218 ();
   testall_rndf (9);
   test_20170105 ();
   check_inexact ();
diff --git a/tests/ttan.c b/tests/ttan.c
index 557168231..393acfe60 100644
--- a/tests/ttan.c
+++ b/tests/ttan.c
@@ -92,6 +92,25 @@ check_nans (void)
   mpfr_clear (y);
 }
 
+/* This test was generated from bad_cases, with GMP_CHECK_RANDOMIZE=1514257254.
+   For the x value below, we have tan(x) = -1.875 + epsilon,
+   thus with RNDZ it should be rounded to -1.c. */
+static void
+bug20171218 (void)
+{
+  mpfr_t x, y, z;
+  mpfr_init2 (x, 804);
+  mpfr_init2 (y, 4);
+  mpfr_init2 (z, 4);
+  mpfr_set_str (x, "-1.14b1dd5f90ce0eded2a8f59c05e72daf7cc4c78f5075d73246fa420e2c026291d9377e67e7f54e925c4aed39c7b2f917424033c8612f00a19821890558d6c2cef9c60f4ad2c3b061ed53a1709dc1ec8e139627c2119c36d7ebdff0d715e559b47f740c534", 16, MPFR_RNDN);
+  mpfr_tan (y, x, MPFR_RNDZ);
+  mpfr_set_str (z, "-1.c", 16, MPFR_RNDN);
+  MPFR_ASSERTN(mpfr_equal_p (y, z));
+  mpfr_clear (x);
+  mpfr_clear (y);
+  mpfr_clear (z);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -102,6 +121,7 @@ main (int argc, char *argv[])
 
   tests_start_mpfr ();
 
+  bug20171218 ();
   check_nans ();
 
   mpfr_init (x);