cuda::narrow

struct narrowing_error;

template <typename To, typename From>
[[nodiscard]] constexpr
To narrow(From from);

template <typename To, typename From>
[[nodiscard]] constexpr
To narrow_cast(From&& __from) noexcept;

Both functions use a static_cast to cast the value from to type To. From needs to be convertible to To, and implement operator!=. cuda::narrow additionally checks whether the value has changed, and if so, throws cuda::narrowing_error in host code and traps in device code. In this case, To additionally needs to be convertible to From. cuda::narrow_cast does not perform such a check (it’s a plain cast) and is just intended to show that narrowing and a potential change of the value is intended. The functions are modelled after gsl::narrow and gsl::narrow_cast. See also the C++ Core Guidelines ES.46 and ES.49.

Example

#include <cuda/numeric>

__global__ void kernel(size_t n) {
    unsigned int r1 = cuda::narrow<unsigned int>(n); // traps

    unsigned int r2 = cuda::narrow_cast<unsigned int>(n); // truncation of value is intended
}

void host() {
    unsigned char r1 = cuda::narrow<unsigned char>( 200); // ok
    unsigned char r2 = cuda::narrow<unsigned char>( 300); // throws narrowing_error
    unsigned int  r3 = cuda::narrow<unsigned int >(-100); // throws narrowing_error

    unsigned char r4 = cuda::narrow_cast<unsigned char>(300); // truncation of value is intended

    kernel<<<1, 1>>>(2LL << 35); // size larger than unsigned int
}

See it on Godbolt 🔗