Fix edge case in 'ash'.

[bpt/guile.git] / libguile / numbers.c

diff --git a/libguile/numbers.c b/libguile/numbers.c
index 6f3a6ec..38c28a4 100644 (file)
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -4978,11 +4978,14 @@ left_shift_exact_integer (SCM n, long count)
     {
       scm_t_inum nn = SCM_I_INUM (n);
 
-      /* Left shift of count >= SCM_I_FIXNUM_BIT-1 will always
+      /* Left shift of count >= SCM_I_FIXNUM_BIT-1 will almost[*] always
          overflow a non-zero fixnum.  For smaller shifts we check the
          bits going into positions above SCM_I_FIXNUM_BIT-1.  If they're
          all 0s for nn>=0, or all 1s for nn<0 then there's no overflow.
-         Those bits are "nn >> (SCM_I_FIXNUM_BIT-1 - count)".  */
+         Those bits are "nn >> (SCM_I_FIXNUM_BIT-1 - count)".
+
+         [*] There's one exception:
+             (-1) << SCM_I_FIXNUM_BIT-1 == SCM_MOST_NEGATIVE_FIXNUM  */
 
       if (nn == 0)
         return n;
@@ -4995,8 +4998,8 @@ left_shift_exact_integer (SCM n, long count)
           SCM result = scm_i_inum2big (nn);
           mpz_mul_2exp (SCM_I_BIG_MPZ (result), SCM_I_BIG_MPZ (result),
                         count);
-          return result;
-        }
+          return scm_i_normbig (result);
+       }
     }
   else if (SCM_BIGP (n))
     {