`<xstd/ints/ext/absl/int128.hpp>`¶

`xstd::make_unsigned<absl::int128>`, `xstd::make_signed<absl::uint128>`¶

// (1)
template<> struct make_unsigned<absl::int128>;

// (2)
template<> struct make_signed<absl::uint128>;

The pairing of Abseil's two 128-bit types, each with the other.

Type	Definition
`type`	the other half of Abseil's pair

Where Abseil has no 128-bit intrinsic, its operator/ and operator% are not constexpr, and neither is a function that divides one.

With the integer-class specializations each half is its own counterpart, the round trip is the identity, the cv-qualifiers carry over, and the pair's limits have the range of [iterator.concept.winc]/3.
With them, absl::int128 models signed_integer and absl::uint128 models unsigned_integer.
The mistakes that port from built-in code stay compile errors for the signed half: div with an int literal divisor, popcount, and align_up.
Abseil declares no noexcept, so the pair models neither nothrow_const_operators nor, for absl::uint128, nothrow_alignable, and the integer functions over it are not noexcept.
The pair hashes as every other 128-bit type does.
The header and its umbrella each compile on their own wherever Abseil is found.

Entity	Relation
`make_signed`, `make_unsigned`	the traits it specializes
`signed_integer`, `unsigned_integer`	what the pair models with it
`nothrow_const_operators`	what the pair does not model
`boost::int128`	the same for Boost's pair