re PR middle-end/21781 (real.c incorrectly values zero with a large exponent)

	PR middle-end/21781
	* real.c (real_from_string): If the mantissa is zero, don't bother
	parsing the exponent as the result should always be zero.

	* gcc.dg/real-const-1.c: New test case.

From-SVN: r112136

1 files changed, 9 insertions, 0 deletions

diff --git a/gcc/real.c b/gcc/real.c
index c4b6479..1e1083f 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -1862,6 +1862,11 @@ real_from_string (REAL_VALUE_TYPE *r, const char *str)
 	      str++;
 	    }
 	}
+
+      /* If the mantissa is zero, ignore the exponent.  */
+      if (!cmp_significand_0 (r))
+	goto underflow;
+
       if (*str == 'p' || *str == 'P')
 	{
 	  bool exp_neg = false;
@@ -1934,6 +1939,10 @@ real_from_string (REAL_VALUE_TYPE *r, const char *str)
 	    }
 	}
 
+      /* If the mantissa is zero, ignore the exponent.  */
+      if (r->cl == rvc_zero)
+	goto underflow;
+
       if (*str == 'e' || *str == 'E')
 	{
 	  bool exp_neg = false;