This guide covers a variety of Abseil libraries related to types, including:
numericalgorithmcontainertypesmetaThe //absl/numeric library provides only one header file at this time:
The int128.h header file defines 128-bit integer types, for use until
intrinsic 128-bit types are part of the C++ standard. Currently, this file
defines only one type: uint128, an unsigned 128-bit integer; a signed 128-bit
integer is forthcoming.
uint128The uint128 type defines an unsigned 128-bit integer. The API is meant to
mimic an intrinsic type as closely as possible, so that any forthcoming
uint128_t can be a drop-in replacement. (uint128 will be removed once C++
supports such a type.)
Note: code written with this type will continue to compile once uint128_t
is introduced, provided the replacement helper functions Uint128(Low|High)64()
and MakeUint128() are made.
A uint128 supports the following:
Additionally, if your compiler supports the __int128 type extension, uint128
is interoperable with that type.
128-bit integer literals are not yet a part of the C++ language. As a result,
to construct a 128-bit unsigned integer with a value greater than 2^64, you will
need to use the absl::MakeUint128() factory function.
Examples:
uint64_t a;
// Implicit conversion from uint64_t OK
uint128 v = a;
// Error: Implicit conversion to uint64_t not OK
uint64_t b = v;
// Explicit conversion to uint64_t OK
uint64_t i = static_cast<uint64_t>(v);
// Construct a value of 2^64
absl::uint128 big = absl::MakeUint128(1, 0);