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4231.datapar::chunk<N> should use simd-size-type instead of size_t
Section: 29.10.3 [simd.syn], 29.10.8.12 [simd.creation] Status: WP Submitter: Matthias Kretz Opened: 2025-03-22 Last modified: 2025-06-23
Priority: Not Prioritized
View all issues with WP status.
Discussion:
All index values and simd widths in subclause "Data-parallel types" use the type simd-size-type. Specifically, the NTTP of std::datapar::resize uses simd-size-type and std::datapar::chunk is "implemented" using std::datapar::resize.
chunk<N>, N is of type size_t and needs to be converted to simd-size-type in the effects clause where it is passed to resize. The NTTP of chunk should use simd-size-type instead of size_t.
[2025-06-13; Reflector poll]
Set status to Tentatively Ready after seven votes in favour during reflector poll.
[Sofia 2025-06-21; Status changed: Voting → WP.]
Proposed resolution:
This wording is relative to N5008.
Modify 29.10.3 [simd.syn], header <simd> synopsis, as indicated:
namespace std::datapar {
[…]
template<simd-size-typesize_t N, class T, class Abi>
constexpr auto chunk(const basic_simd<T, Abi>& x) noexcept;
template<simd-size-typesize_t N, size_t Bytes, class Abi>
constexpr auto chunk(const basic_simd_mask<Bytes, Abi>& x) noexcept;
[…]
}
Modify 29.10.8.12 [simd.creation] as indicated:
template<simd-size-typesize_t N, class T, class Abi> constexpr auto chunk(const basic_simd<T, Abi>& x) noexcept;-4- Effects: Equivalent to:
return chunk<resize_t<N, basic_simd<T, Abi>>>(x);template<simd-size-typesize_t N, size_t Bytes, class Abi> constexpr auto chunk(const basic_simd_mask<Bytes, Abi>& x) noexcept;-5- Effects: Equivalent to:
return chunk<resize_t<N, basic_simd_mask<Bytes, Abi>>>(x);
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