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

gcc/ChangeLog

+2006-03-16  Roger Sayle  <roger@eyesopen.com>
+
+	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.
+
 2006-03-16  Andreas Krebbel  <krebbel1@de.ibm.com>
 
 	* simplify-rtx.c (simplify_plus_minus): Simplify within CONST terms.

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;

gcc/testsuite/ChangeLog

+2006-03-16  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/21781
+	* gcc.dg/real-const-1.c: New test case.
+
 2006-03-15  Geoffrey Keating  <geoffk@apple.com>
 
 	* g++.old-deja/g++.other/init18.C: New.

gcc/testsuite/gcc.dg/real-const-1.c

+/* PR middle-end/21781.  */
+/* { dg-do compile } */
+
+int f[.0e200000000 == 0?1:-1];