fixed bug in mpfr_pow found by Ming J. Tsai (overflow)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@2487 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 16 insertions, 1 deletions

diff --git a/pow.c b/pow.c
index f6cc45a3c..7c965f632 100644
--- a/pow.c
+++ b/pow.c
@@ -240,7 +240,7 @@ mpfr_pow (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y, mp_rnd_t rnd_mode)
     {
       int negative;
       /* Determine the sign now, in case y and z are the same object */
-      negative = MPFR_SIGN(x) < 0 && is_odd(y);
+      negative = MPFR_SIGN(x) < 0 && is_odd (y);
       MPFR_CLEAR_FLAGS(z);
       if (MPFR_SIGN(y) < 0)
         MPFR_SET_INF(z);
@@ -258,6 +258,21 @@ mpfr_pow (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y, mp_rnd_t rnd_mode)
       MPFR_RET(0);
     }
 
+  /* detect overflows: |x^y| >= 2^EMAX when (EXP(x)-1) * y >= EMAX for y > 0,
+                                       or   EXP(x) * y     >= EMAX for y < 0 */
+  {
+    double exy;
+    int negative;
+
+    exy = (double) (mpfr_sgn (y) > 0) ? MPFR_EXP(x) - 1 : MPFR_EXP(x);
+    exy *= mpfr_get_d (y, GMP_RNDZ);
+    if (exy >= (double) __gmpfr_emax)
+      {
+        negative = MPFR_SIGN(x) < 0 && is_odd (y);
+        return mpfr_set_overflow (z, rnd_mode, negative ? -1 : 1);
+      }
+  }  
+
   if (mpfr_integer_p (y))
     {
       mpz_t zi;