fixed infinite loop for 2^integer

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@2134 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 17 insertions, 4 deletions

diff --git a/exp2.c b/exp2.c
index 6f93c8eec..1d2bb43ba 100644
--- a/exp2.c
+++ b/exp2.c
@@ -24,16 +24,16 @@ MA 02111-1307, USA. */
 #include "mpfr.h"
 #include "mpfr-impl.h"
 
- /* The computation of y=pow(2,z) is done by
+ /* The computation of y = 2^z is done by
 
-    y=exp(z*log(2))=2^z
+    y = exp(z*log(2)). The result is exact iff z is an integer.
  */
 
 int
 mpfr_exp2 (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode) 
 {    
 
-    int inexact =0;
+    int inexact;
 
     if (MPFR_IS_NAN(x))
       {
@@ -67,6 +67,19 @@ mpfr_exp2 (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode)
     if (mpfr_cmp_si_2exp (x, __gmpfr_emin - 1, 0) < 0)
       return mpfr_set_underflow (y, rnd_mode, 1);
 
+    if (mpfr_isinteger (x)) /* we know that x >= 2^(emin-1) */
+      {
+        double xd;
+
+        if (mpfr_cmp_si_2exp (x, __mpfr_emax, 0) > 0)
+          return mpfr_set_overflow (y, rnd_mode, 1);
+
+        xd = mpfr_get_d1 (x);
+        
+        mpfr_set_ui (y, 1, GMP_RNDZ);
+        return mpfr_mul_2si (y, y, (long) xd, rnd_mode);
+      }
+
     /* General case */
     {
     /* Declaration of the intermediary variable */
@@ -114,6 +127,6 @@ mpfr_exp2 (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode)
       mpfr_clear (t);
       mpfr_clear (te);
     }
-    return inexact;
 
+    return inexact;
 }