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Re: [PATCH] Simplify overflow checks in duration literals

On 14/08/18 09:59 -0400, Marek Polacek wrote:
On Tue, Aug 14, 2018 at 02:55:17PM +0100, Jonathan Wakely wrote:
	* include/std/chrono (__check_overflow): Simplify definition.
	(_Checked_integral_constant): Remove.

Tested x86_64-linux, committed to trunk.

commit c0dec9d05de4695136694f78f2f76e3c9f15b3f1
Author: Jonathan Wakely <>
Date:   Tue Aug 14 14:33:38 2018 +0100

    Simplify overflow checks in duration literals

            * include/std/chrono (__check_overflow): Simplify definition.
            (_Checked_integral_constant): Remove.

diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index da03fdccce4..871c896144a 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wliteral-suffix"
-    template<typename _Rep, unsigned long long _Val>
-      struct _Checked_integral_constant
-      : integral_constant<_Rep, static_cast<_Rep>(_Val)>
-      {
-	static_assert(_Checked_integral_constant::value >= 0
-		      && _Checked_integral_constant::value == _Val,
-		      "literal value cannot be represented by duration type");
-      };
     template<typename _Dur, char... _Digits>
       constexpr _Dur __check_overflow()
 	using _Val = __parse_int::_Parse_int<_Digits...>;
-	using _Rep = typename _Dur::rep;
-	// TODO: should be simply integral_constant<_Rep, _Val::value>
-	// but GCC doesn't reject narrowing conversions to _Rep.

Note that I fixed 57891 yesterday.  Or is this either 65043 or 78244?

Yes, thanks for that! That was what made me revisit the TODO. But
using integral_constant there doesn't produce the required error,
because it's in a system header. The standard requires it to be
ill-formed, so I can't rely on the narrowing diagnostic :-(

But I realised it could be simplified anyway (and that could have been
done years ago, without waiting for the fixes to narrowing in template

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