Fixed bug in mpfr_pow_z: if x = y (same mpfr_t argument), the input

argument is negative and not a power of two, z is positive and odd,
an overflow or underflow occurs, and the temporary result res is
positive, then the result gets a wrong sign (positive instead of
negative). Testcase.


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@5110 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 49 insertions, 11 deletions

diff --git a/pow_z.c b/pow_z.c
index ab1efa6b6..23170b20e 100644
--- a/pow_z.c
+++ b/pow_z.c
@@ -81,21 +81,19 @@ mpfr_pow_pos_z (mpfr_ptr y, mpfr_srcptr x, mpz_srcptr z, mp_rnd_t rnd)
     }
   MPFR_ZIV_FREE (loop);
 
-  inexact = mpfr_set (y, res, rnd);
-  mpfr_clear (res);
-
   /* Check Overflow */
   if (MPFR_UNLIKELY (mpfr_overflow_p ()))
-    return mpfr_overflow (y, rnd,
-              mpz_odd_p (absz) ? MPFR_SIGN (x) : MPFR_SIGN_POS);
+    inexact = mpfr_overflow (y, rnd, mpz_odd_p (absz) ?
+                             MPFR_SIGN (x) : MPFR_SIGN_POS);
   /* Check Underflow */
   else if (MPFR_UNLIKELY (mpfr_underflow_p ()))
-    {
-      if (rnd == GMP_RNDN)
-        rnd = GMP_RNDZ;
-      return mpfr_underflow (y, rnd,
-         mpz_odd_p (absz) ? MPFR_SIGN (x) : MPFR_SIGN_POS);
-    }
+    inexact = mpfr_underflow (y, rnd == GMP_RNDN ? GMP_RNDZ : rnd,
+                              mpz_odd_p (absz) ? MPFR_SIGN (x) :
+                              MPFR_SIGN_POS);
+  else
+    inexact = mpfr_set (y, res, rnd);
+
+  mpfr_clear (res);
   return inexact;
 }
 
diff --git a/tests/tpow_z.c b/tests/tpow_z.c
index 0fb71ba19..d4da4ecbe 100644
--- a/tests/tpow_z.c
+++ b/tests/tpow_z.c
@@ -257,6 +257,45 @@ bug20071104 (void)
   mpz_clear (z);
 }
 
+static void
+check_overflow (void)
+{
+  mpfr_t a;
+  mpz_t z;
+  unsigned long n;
+  int res;
+
+  mpfr_init2 (a, 53);
+
+  mpfr_set_str_binary (a, "1E10");
+  mpz_init_set_ui (z, ULONG_MAX);
+  res = mpfr_pow_z (a, a, z, GMP_RNDN);
+  if (!MPFR_IS_INF (a) || MPFR_SIGN (a) < 0)
+    {
+      printf ("Error for (1e10)^ULONG_MAX\n");
+      exit (1);
+    }
+
+  /* Bug in pow_z.c up to r5109: if x = y (same mpfr_t argument), the
+     input argument is negative and not a power of two, z is positive
+     and odd, an overflow or underflow occurs, and the temporary result
+     res is positive, then the result gets a wrong sign (positive
+     instead of negative). */
+  mpfr_set_str_binary (a, "-1.1E10");
+  n = (ULONG_MAX ^ (ULONG_MAX >> 1)) + 1;
+  mpz_set_ui (z, n);
+  res = mpfr_pow_z (a, a, z, GMP_RNDN);
+  if (!MPFR_IS_INF (a) || MPFR_SIGN (a) > 0)
+    {
+      printf ("Error for (-1e10)^%lu, expected -Inf,\ngot ", n);
+      mpfr_dump (a);
+      exit (1);
+    }
+
+  mpfr_clear (a);
+  mpz_clear (z);
+}
+
 int
 main (void)
 {
@@ -266,6 +305,7 @@ main (void)
   check_integer (2, 163, 100);
   check_regression ();
   bug20071104 ();
+  check_overflow ();
 
   tests_end_mpfr ();
   return 0;