Configuration Macros

BOOST_INT128_ENABLE_CUDA: Defining this macro allows both types and selected functions to be run on both host and device when compiling with NVCC. Allowed functions have BOOST_INT128_HOST_DEVICE as part of their function signature in their documentation.

BOOST_INT128_ENABLE_SYCL: Defining this macro allows both types and selected functions to be run on the device when compiling with a SYCL compiler (for example Intel oneAPI icpx -fsycl). Unlike CUDA, SYCL device support is opt-in and is not detected automatically, so this macro must be defined and <sycl/sycl.hpp> must be included before any Boost.int128 header (so that SYCL_EXTERNAL is available). Device-enabled functions have BOOST_INT128_HOST_DEVICE as part of their function signature in their documentation. The boost::charconv::to_chars / from_chars overloads in <boost/int128/charconv.hpp> also run on the SYCL device: defining BOOST_INT128_ENABLE_SYCL forwards to BOOST_CHARCONV_ENABLE_SYCL, and Boost.Charconv provides matching SYCL device support (as it does for CUDA).

BOOST_INT128_NO_BUILTIN_INT128: The user may define this when they do not want the internal implementations to rely on builtin __int128 or unsigned __int128 types.

BOOST_INT128_DISABLE_EXCEPTIONS: Allows exceptions to be disabled. This macro will automatically be defined in the presence of -fno-exceptions or similar MSVC flags.

BOOST_INT128_BUILD_MODULE: Define this when building the library as a C++20 named module (consumed via import boost.int128). It switches the headers into module mode by exporting the public interface and suppressing the includes that the module unit itself provides. See Getting Started.

BOOST_INT128_HAS_INT128: This is defined when compiling on a platform that has builtin __int128 or unsigned __int128 types (e.g. __x86_64__).

BOOST_INT128_ENDIAN_LITTLE_BYTE: This is defined to 1 when compiling on a little endian architecture, otherwise 0.

BOOST_INT128_ENDIAN_BIG_BYTE: This is defined to 1 when compiling on a big endian architecture, otherwise 0.

BOOST_INT128_HAS_MSVC_INT128: This is defined when the MSVC standard library provides the simulated 128-bit integer types in <__msvc_int128.hpp> (MSVC in C++20 mode). When defined, the library uses those types as its native 128-bit backing.

BOOST_INT128_HAS_GPU_SUPPORT: This is defined when the library is compiled with device support enabled, that is under either BOOST_INT128_ENABLE_CUDA (with NVCC) or BOOST_INT128_ENABLE_SYCL. It is the single check for whether a GPU device target is in play. Note that on the SYCL device pass the library falls back to its portable path because the spir64 target has no native __int128, so BOOST_INT128_HAS_INT128 is not defined there.

BOOST_INT128_HAS_SPACESHIP_OPERATOR: This is defined when the compiler and standard library provide C++20 three-way comparison (operator<⇒ and <compare>). When defined, both types provide operator<⇒.

BOOST_INT128_HAS_FORMAT: This is defined by <boost/int128/format.hpp> when C++20 <format> is available. When defined, that header provides std::formatter specializations for both types.

BOOST_INT128_HAS_FMT_FORMAT: This is defined by <boost/int128/fmt_format.hpp> when the {fmt} library is available. When defined, that header provides fmt::formatter specializations for both types.

BOOST_INT128_HOST_DEVICE: This is defined to __host__ __device__ when compiling for CUDA (__CUDACC__ with BOOST_INT128_ENABLE_CUDA), to SYCL_EXTERNAL when compiling for SYCL (BOOST_INT128_ENABLE_SYCL), and to nothing otherwise. The core type operations (constructors, conversion operators, and the comparison, bitwise, arithmetic, and shift operators) and most free functions are annotated with this macro, allowing int128_t and uint128_t to be used in CUDA and SYCL device code. Host-only integrations that depend on host facilities are not annotated: std::hash, the iostream operators, the std::formatter / {fmt} support, and the core::string_view overloads of from_chars. Under SYCL the operator long double conversion is additionally unavailable because the spir64 device target has no long double.