[src/jyn_asympt.c] Fixed bug when sin(z)±cos(z) rounds to 0.

[tests/tj0.c] Testcase.
(merged changesets r14400,14405 from the trunk)

git-svn-id: https://scm.gforge.inria.fr/anonscm/svn/mpfr/branches/4.1@14426 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 34 insertions, 2 deletions

diff --git a/src/jyn_asympt.c b/src/jyn_asympt.c
index 86fefe4c4..6e5c7c37d 100644
--- a/src/jyn_asympt.c
+++ b/src/jyn_asympt.c
@@ -69,6 +69,8 @@ FUNCTION (mpfr_ptr res, long n, mpfr_srcptr z, mpfr_rnd_t r)
   MPFR_ZIV_INIT (loop, w);
   for (;;)
     {
+      int ok = 1;
+
       mpfr_set_prec (c, w);
       mpfr_init2 (s, w);
       mpfr_init2 (P, w);
@@ -92,6 +94,13 @@ FUNCTION (mpfr_ptr res, long n, mpfr_srcptr z, mpfr_rnd_t r)
       /* now s approximates sin(z)+cos(z), and c approximates sin(z)-cos(z),
          with total absolute error bounded by 2^(1-w). */
 
+      /* if s or c is zero, MPFR_GET_EXP will fail below */
+      if (MPFR_IS_ZERO(s) || MPFR_IS_ZERO(c))
+        {
+          ok = 0;
+          goto clear;
+        }
+
       /* precompute 1/(8|z|) */
       mpfr_si_div (iz, MPFR_IS_POS(z) ? 1 : -1, z, MPFR_RNDN);   /* err <= 1 */
       mpfr_div_2ui (iz, iz, 3, MPFR_RNDN);
@@ -257,6 +266,9 @@ FUNCTION (mpfr_ptr res, long n, mpfr_srcptr z, mpfr_rnd_t r)
       err = (err >= err2) ? err + 1 : err2 + 1;
       /* the absolute error on c is bounded by 2^(err - w) */
 
+      err -= MPFR_GET_EXP (c);
+
+    clear:
       mpfr_clear (s);
       mpfr_clear (P);
       mpfr_clear (Q);
@@ -266,8 +278,7 @@ FUNCTION (mpfr_ptr res, long n, mpfr_srcptr z, mpfr_rnd_t r)
       mpfr_clear (err_s);
       mpfr_clear (err_u);
 
-      err -= MPFR_GET_EXP (c);
-      if (MPFR_LIKELY (MPFR_CAN_ROUND (c, w - err, MPFR_PREC(res), r)))
+      if (ok && MPFR_LIKELY (MPFR_CAN_ROUND (c, w - err, MPFR_PREC(res), r)))
         break;
       if (diverge != 0)
         {
diff --git a/tests/tj0.c b/tests/tj0.c
index 14e30bf6d..6f6f02124 100644
--- a/tests/tj0.c
+++ b/tests/tj0.c
@@ -27,6 +27,25 @@ https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
 #define REDUCE_EMAX 262143 /* otherwise arg. reduction is too expensive */
 #include "tgeneric.c"
 
+/* bug found in revision 14399 with GMP_CHECK_RANDOMIZE=1612721106588971 */
+static void
+bug20210208 (void)
+{
+  mpfr_t x, y;
+  int inex;
+
+  mpfr_init2 (x, 79);
+  mpfr_init2 (y, 1);
+  mpfr_set_str (x, "2.552495117262005805960565e+02", 10, MPFR_RNDN);
+  mpfr_clear_flags ();
+  inex = mpfr_j0 (y, x, MPFR_RNDZ);
+  MPFR_ASSERTN (mpfr_cmp_si_2exp (y, -1, -5) == 0);
+  MPFR_ASSERTN (inex > 0);
+  MPFR_ASSERTN (__gmpfr_flags == MPFR_FLAGS_INEXACT);
+  mpfr_clear (x);
+  mpfr_clear (y);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -35,6 +54,8 @@ main (int argc, char *argv[])
 
   tests_start_mpfr ();
 
+  bug20210208 ();
+
   mpfr_init (x);
   mpfr_init (y);