[Ada] Ensure that Scan_Real result does not depend on trailing zeros

Previous change in that procedure to handle overflow issues during
scanning removed the special handling for trailing zeros in the decimal
part. Beside the absence of overflow during scanning the special
handling of these zeros is still necessary.

2019-09-18  Nicolas Roche  <roche@adacore.com>

gcc/ada/

	* libgnat/s-valrea.adb (Scan_Integral_Digits): New procedure.
	(Scan_Decimal_Digits): New procedure.
	(As_Digit): New function.
	(Scan_Real): Use Scan_Integral_Digits and Scan_Decimal_Digits.

gcc/testsuite/

	* gnat.dg/float_value2.adb: New testcase.

From-SVN: r275849

gcc/ada/ChangeLog

+2019-09-18  Nicolas Roche  <roche@adacore.com>
+
+	* libgnat/s-valrea.adb (Scan_Integral_Digits): New procedure.
+	(Scan_Decimal_Digits): New procedure.
+	(As_Digit): New function.
+	(Scan_Real): Use Scan_Integral_Digits and Scan_Decimal_Digits.
+
 2019-09-18  Claire Dross  <dross@adacore.com>
 
 	* exp_attr.adb (Expand_N_Attribute_Reference): Call routine from

gcc/testsuite/ChangeLog

+2019-09-18  Nicolas Roche  <roche@adacore.com>
+
+	* gnat.dg/float_value2.adb: New testcase.
+
 2019-09-18  Vadim Godunko  <godunko@adacore.com>
 
 	* gnat.dg/expect4.adb: New testcase.

gcc/testsuite/gnat.dg/float_value2.adb

+--  { dg-do run }
+
+procedure Float_Value2 is
+   F1 : Long_Long_Float := Long_Long_Float'Value ("1.e40");
+   F2 : Long_Long_Float := Long_Long_Float'Value ("1.0e40");
+begin
+   if F1 /= F2 then
+      raise Program_Error;
+   end if;
+end Float_Value2;
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