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libstdc++: Implement LWG 3403 for std::ranges::ssize

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I already changed the constraints for ranges::ssize to use ranges::size,
this implements the rest of LWG 3403, so that the returned type is the
signed type corresponding to the result of ranges::size.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/ranges_base.h (_SSize): Return the result of
	ranges::size converted to the wider of make-signed-like-t<S> and
	ptrdiff_t, rather than the ranges different type.
	* testsuite/std/ranges/access/ssize.cc: Adjust expected result
	for an iota_view that uses an integer class type for its
	difference_type.
This commit is contained in:
Jonathan Wakely 2021-06-04 20:28:04 +01:00
parent 3e5f2425f8
commit 621ea10ca0
2 changed files with 22 additions and 9 deletions
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22
libstdc++-v3/include/bits/ranges_base.h
View File

@ -425,22 +425,32 @@ namespace ranges
struct _SSize
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3403. Domain of ranges::ssize(E) doesn't match ranges::size(E)
template<typename _Tp>
requires requires (_Tp& __t) { _Size{}(__t); }
constexpr auto
operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
{
using __iter_type = decltype(_Begin{}(__t));
using __diff_type = iter_difference_t<__iter_type>;
using __gnu_cxx::__int_traits;
auto __size = _Size{}(__t);
if constexpr (integral<__diff_type>)
using __size_type = decltype(__size);
// Return the wider of ptrdiff_t and make-signed-like-t<__size_type>.
if constexpr (integral<__size_type>)
{
if constexpr (__int_traits<__diff_type>::__digits
using __gnu_cxx::__int_traits;
if constexpr (__int_traits<__size_type>::__digits
< __int_traits<ptrdiff_t>::__digits)
return static_cast<ptrdiff_t>(__size);
else
return static_cast<make_signed_t<__size_type>>(__size);
}
return static_cast<__diff_type>(__size);
#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
// For strict-ansi modes integral<__int128> is false
else if constexpr (__detail::__is_int128<__size_type>)
return static_cast<unsigned __int128>(__size);
#endif
else // Must be one of __max_diff_type or __max_size_type.
return __detail::__max_diff_type(__size);
}
};

9
libstdc++-v3/testsuite/std/ranges/access/ssize.cc
View File

@ -76,9 +76,12 @@ void
test06()
{
auto i = std::views::iota(1ull, 5u);
auto s = std::ranges::ssize(i);
using R = std::ranges::range_difference_t<decltype(i)>;
static_assert( std::same_as<decltype(s), R> );
auto s = std::ranges::size(i);
auto ss = std::ranges::ssize(i);
// std::ranges::range_difference_t<decltype(i)> is larger than long long,
// but LWG 3403 says ranges::ssize(i) returns the signed version of the
// type that ranges::size(i) returns, not the range's difference_type.
static_assert( std::same_as<decltype(ss), std::make_signed_t<decltype(s)>> );
VERIFY( s == 4 );
}