[gcc r16-4091] libstdc++: Refactor __mdspan::__static_quotient.

[Tomasz Kaminski]

https://gcc.gnu.org/g:5756d0b61317b28922e5c7a9ce30f0aca19b901d

commit r16-4091-g5756d0b61317b28922e5c7a9ce30f0aca19b901d
Author: Luc Grosheintz <luc.grosheintz@gmail.com>
Date:   Tue Sep 23 15:10:04 2025 +0200

    libstdc++: Refactor __mdspan::__static_quotient.
    
    For padded layouts we want to check that the product of the
    padded stride with the remaining extents is representable.
    
    Creating a second overload, allows passing in subspans of the
    static extents and retains the ergonomics for the common case
    of passing in all static extents.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/mdspan (__static_quotient): New overload.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>

Diff:
---
 libstdc++-v3/include/std/mdspan | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 01d3b2cb6b17..d9b5152b6938 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -597,13 +597,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return __res;
       }
 
-    template<typename _Extents,
-             typename _IndexType = typename _Extents::index_type>
+    template<typename _IndexType>
       consteval _IndexType
-      __static_quotient(_IndexType __nom = __gnu_cxx::__int_traits<_IndexType>
-						    ::__max)
+      __static_quotient(std::span<const size_t> __sta_exts,
+	_IndexType __nom = __gnu_cxx::__int_traits<_IndexType>::__max)
       {
-	std::span<const size_t> __sta_exts = __static_extents<_Extents>();
 	for (auto __factor : __sta_exts)
 	  {
 	    if (__factor != dynamic_extent)
@@ -614,6 +612,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return __nom;
       }
 
+    template<typename _Extents,
+	     typename _IndexType = typename _Extents::index_type>
+      requires __is_extents<_Extents>
+      consteval _IndexType
+      __static_quotient(_IndexType __nom
+			  = __gnu_cxx::__int_traits<_IndexType>::__max)
+      {
+	std::span<const size_t> __sta_exts = __static_extents<_Extents>();
+	return __static_quotient<_IndexType>(__sta_exts, __nom);
+      }
+
     template<typename _Extents>
       constexpr bool
       __is_representable_extents(const _Extents& __exts) noexcept