This implements signed and unsigned integer-class types, whose width is
one bit larger than the widest supported signed and unsigned integral
type respectively. In our case this is either __int128 and unsigned
__int128, or long long and unsigned long long.
Internally, the two integer-class types are represented as a largest
supported unsigned integral type plus one extra bit. The signed
integer-class type is represented in two's complement form with the
extra bit acting as the sign bit.
libstdc++-v3/ChangeLog:
* include/Makefile.am (bits_headers): Add new header
<bits/max_size_type.h>.
* include/Makefile.in: Regenerate.
* include/bits/iterator_concepts.h
(ranges::__detail::__max_diff_type): Remove definition, replace
with forward declaration of class __max_diff_type.
(__detail::__max_size_type): Remove definition, replace with
forward declaration of class __max_size_type.
(__detail::__is_unsigned_int128, __is_signed_int128)
(__is_int128): New concepts.
(__detail::__is_integer_like): Accept __int128 and unsigned
__int128.
(__detail::__is_signed_integer_like): Accept __int128.
* include/bits/max_size_type.h: New header.
* include/bits/range_access.h: Include <bits/max_size_type.h>.
(__detail::__to_unsigned_like): Two new overloads.
* testsuite/std/ranges/iota/difference_type.cc: New test.
* testsuite/std/ranges/iota/max_size_type.cc: New test.
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