Literals
The following literals and macros are provided for convenient construction of the types provided in the library.
#include <boost/int128/literals.hpp>
namespace boost {
namespace int128 {
namespace literals {
BOOST_INT128_HOST_DEVICE constexpr uint128_t operator ""_u128(const char* str) noexcept;
BOOST_INT128_HOST_DEVICE constexpr uint128_t operator ""_U128(const char* str) noexcept;
BOOST_INT128_HOST_DEVICE constexpr uint128_t operator ""_u128(const char* str, std::size_t len) noexcept;
BOOST_INT128_HOST_DEVICE constexpr uint128_t operator ""_U128(const char* str, std::size_t len) noexcept;
BOOST_INT128_HOST_DEVICE constexpr int128_t operator ""_i128(const char* str) noexcept;
BOOST_INT128_HOST_DEVICE constexpr int128_t operator ""_I128(const char* str) noexcept;
BOOST_INT128_HOST_DEVICE constexpr int128_t operator ""_i128(const char* str, std::size_t len) noexcept;
BOOST_INT128_HOST_DEVICE constexpr int128_t operator ""_I128(const char* str, std::size_t len) noexcept;
} // namespace literals
} // namespace int128
} // namespace boost
#define BOOST_INT128_UINT128_C(x) ...
#define BOOST_INT128_INT128_C(x) ...The macros at the end allow you to write out a 128-bit number like you would with say UINT64_C without having to add quotes.
See the construction examples for usage demonstrations of both literals and macros.
Design Rationale
All of the user-defined literals provided by the library are string-form: the operator receives a const char* and parses the digit sequence via from_chars.
This holds even for raw numeric tokens like 12345_U128, which the compiler forwards to the operator as the string "12345".
The choice is intentional.
A 128-bit value cannot be represented by unsigned long long, so any literal whose magnitude exceeds 2^64 must go through a string-based parse.
Providing only the string form means there is a single overload that handles every magnitude uniformly, rather than a numeric form for small values and a string form for large ones with a hard cutoff at 2^64.
The API is the same regardless of how large the value is.
The trade-off is that every literal pays the cost of parsing, even when the value would fit in a builtin integer.
For values smaller than 2^64, prefer the constructor:
constexpr uint128_t small {42U}; // direct conversion from a builtin
const auto small_literal {42_U128}; // parses "42" via from_charsThe two produce the same value, but the constructor avoids the parse and should be used in hot paths or in code where many small constants are constructed.