[gcc r13-3935] libstdc++: Allow std::to_chars for 128-bit integers in strict mode

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:d4ba3b369cbe9bce0a1212670825ecfb99762520

commit r13-3935-gd4ba3b369cbe9bce0a1212670825ecfb99762520
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Nov 1 09:48:41 2022 +0000

    libstdc++: Allow std::to_chars for 128-bit integers in strict mode
    
    This allows std::format to support __int128 when __STRICT_ANSI__ is
    defined, which previously failed because __int128 is not an integral
    type in strict mode.
    
    With these changes, std::to_chars still rejects 128-bit integers in
    strict mode, but std::format will be able to use __detail::__to_chars_i
    for unsigned __int128.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/charconv.h (__integer_to_chars_is_unsigned):
            New variable template.
            (__to_chars_len, __to_chars_10_impl): Use variable template in
            assertions to allow unsigned __int128 in strict mode.
            * include/std/charconv (__to_chars, __to_chars_16)
            (__to_chars_10, __to_chars_8, __to_chars_2): Likewise.

Diff:
---
 libstdc++-v3/include/bits/charconv.h | 18 ++++++++++++++----
 libstdc++-v3/include/std/charconv    | 19 +++++++++----------
 2 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/libstdc++-v3/include/bits/charconv.h b/libstdc++-v3/include/bits/charconv.h
index d04aab77624..103cfcb8177 100644
--- a/libstdc++-v3/include/bits/charconv.h
+++ b/libstdc++-v3/include/bits/charconv.h
@@ -35,19 +35,28 @@
 #if __cplusplus >= 201103L
 
 #include <type_traits>
+#include <ext/numeric_traits.h>
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 namespace __detail
 {
+#if __cpp_variable_templates
+  // This accepts 128-bit integers even in strict mode.
+  template<typename _Tp>
+    constexpr bool __integer_to_chars_is_unsigned
+      = ! __gnu_cxx::__int_traits<_Tp>::__is_signed;
+#endif
+
   // Generic implementation for arbitrary bases.
   template<typename _Tp>
     _GLIBCXX14_CONSTEXPR unsigned
     __to_chars_len(_Tp __value, int __base = 10) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+#if __cpp_variable_templates
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
+#endif
 
       unsigned __n = 1;
       const unsigned __b2 = __base  * __base;
@@ -71,8 +80,9 @@ namespace __detail
     _GLIBCXX23_CONSTEXPR void
     __to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+#if __cpp_variable_templates
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
+#endif
 
       constexpr char __digits[201] =
 	"0001020304050607080910111213141516171819"
diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index c5ed6fac73b..8f02395172f 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -88,6 +88,10 @@ namespace __detail
     using __integer_to_chars_result_type
       = enable_if_t<__or_<__is_signed_integer<_Tp>,
 			  __is_unsigned_integer<_Tp>,
+#if defined __SIZEOF_INT128__ && defined __STRICT_ANSI__
+			  is_same<_Tp, signed __int128>,
+			  is_same<_Tp, unsigned __int128>,
+#endif
 			  is_same<char, remove_cv_t<_Tp>>>::value,
 		    to_chars_result>;
 
@@ -126,8 +130,7 @@ namespace __detail
     constexpr to_chars_result
     __to_chars(char* __first, char* __last, _Tp __val, int __base) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;
 
@@ -167,8 +170,7 @@ namespace __detail
     constexpr __integer_to_chars_result_type<_Tp>
     __to_chars_16(char* __first, char* __last, _Tp __val) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;
 
@@ -214,8 +216,7 @@ namespace __detail
     constexpr __integer_to_chars_result_type<_Tp>
     __to_chars_10(char* __first, char* __last, _Tp __val) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;
 
@@ -238,8 +239,7 @@ namespace __detail
     constexpr __integer_to_chars_result_type<_Tp>
     __to_chars_8(char* __first, char* __last, _Tp __val) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;
       unsigned __len;
@@ -292,8 +292,7 @@ namespace __detail
     constexpr __integer_to_chars_result_type<_Tp>
     __to_chars_2(char* __first, char* __last, _Tp __val) noexcept
     {
-      static_assert(is_integral<_Tp>::value, "implementation bug");
-      static_assert(is_unsigned<_Tp>::value, "implementation bug");
+      static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;