[src/strtofr.c] Fixed bug in mpfr_strtofr(): in round-to-nearest,

  the ternary value could be incorrect.
[tests/tstrtofr.c] Added test case.
(merged changesets from the trunk: r11055, a part of r11056, and
r11059,11066-11068)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/3.1@11069 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 27 insertions, 5 deletions

diff --git a/src/strtofr.c b/src/strtofr.c
index 67f5caa62..a1904cc04 100644
--- a/src/strtofr.c
+++ b/src/strtofr.c
@@ -743,11 +743,14 @@ parsed_string_to_mpfr (mpfr_t x, struct parsed_string *pstr, mpfr_rnd_t rnd)
          of the pstr_size most significant digits of pstr->mant, with
          equality in case exact is non-zero. */
 
-      /* test if rounding is possible, and if so exit the loop */
-      if (exact || mpfr_can_round_raw (result, ysize,
-                                       (pstr->negative) ? -1 : 1,
-                                       ysize_bits - err - 1,
-                                       MPFR_RNDN, rnd, MPFR_PREC(x)))
+      /* test if rounding is possible, and if so exit the loop.
+         Note: we also need to be able to determine the correct ternary value,
+         thus we use the MPFR_PREC(x) + (rnd == MPFR_RNDN) trick.
+         For example if result = xxx...xxx111...111 and rnd = RNDN,
+         then we know the correct rounding is xxx...xx(x+1), but we cannot know
+         the correct ternary value. */
+      if (exact || mpfr_round_p (result, ysize, ysize_bits - err - 1,
+                                 MPFR_PREC(x) + (rnd == MPFR_RNDN)))
         break;
 
     next_loop:
diff --git a/tests/tstrtofr.c b/tests/tstrtofr.c
index 97575413a..46b76c625 100644
--- a/tests/tstrtofr.c
+++ b/tests/tstrtofr.c
@@ -1191,6 +1191,24 @@ bug20120829 (void)
   mpfr_clears (e, x1, x2, (mpfr_ptr) 0);
 }
 
+/* Note: the number is 5^47/2^9. */
+static void
+bug20161217 (void)
+{
+  mpfr_t fp, z;
+  static const char * num = "0.1387778780781445675529539585113525390625e31";
+  int inex;
+
+  mpfr_init2 (fp, 110);
+  mpfr_init2 (z, 110);
+  inex = mpfr_strtofr (fp, num, NULL, 10, MPFR_RNDN);
+  MPFR_ASSERTN(inex == 0);
+  mpfr_set_str_binary (z, "10001100001000010011110110011101101001010000001011011110010001010100010100100110111101000010001011001100001101E-9");
+  MPFR_ASSERTN(mpfr_equal_p (fp, z));
+  mpfr_clear (fp);
+  mpfr_clear (z);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -1205,6 +1223,7 @@ main (int argc, char *argv[])
   test20100310 ();
   bug20120814 ();
   bug20120829 ();
+  bug20161217 ();
 
   tests_end_mpfr ();
   return 0;