56 lines
1.9 KiB
ReStructuredText
56 lines
1.9 KiB
ReStructuredText
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.. _libcudacxx-extended-api-numeric-narrow:
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``cuda::narrow``
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=====================
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.. code:: cpp
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struct narrowing_error;
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template <typename To, typename From>
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[[nodiscard]] constexpr
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To narrow(From from);
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template <typename To, typename From>
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[[nodiscard]] constexpr
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To narrow_cast(From&& __from) noexcept;
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Both functions use a ``static_cast`` to cast the value ``from`` to type ``To``.
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``From`` needs to be convertible to ``To``, and implement ``operator!=``.
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``cuda::narrow`` additionally checks whether the value has changed,
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and if so, throws ``cuda::narrowing_error`` in host code and traps in device code.
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In this case, ``To`` additionally needs to be convertible to ``From``.
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``cuda::narrow_cast`` does not perform such a check (it's a plain cast) and is just intended to show
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that narrowing and a potential change of the value is intended.
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The functions are modelled after ``gsl::narrow`` and ``gsl::narrow_cast``.
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See also the C++ Core Guidelines
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`ES.46 <https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-narrowing>`_ and
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`ES.49 <https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-casts-named>`_.
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Example
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-------
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.. code:: cpp
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#include <cuda/numeric>
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__global__ void kernel(size_t n) {
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unsigned int r1 = cuda::narrow<unsigned int>(n); // traps
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unsigned int r2 = cuda::narrow_cast<unsigned int>(n); // truncation of value is intended
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}
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void host() {
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unsigned char r1 = cuda::narrow<unsigned char>( 200); // ok
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unsigned char r2 = cuda::narrow<unsigned char>( 300); // throws narrowing_error
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unsigned int r3 = cuda::narrow<unsigned int >(-100); // throws narrowing_error
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unsigned char r4 = cuda::narrow_cast<unsigned char>(300); // truncation of value is intended
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kernel<<<1, 1>>>(2LL << 35); // size larger than unsigned int
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}
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`See it on Godbolt 🔗 <https://godbolt.org/z/ahcqv6joY>`_
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