C++26 Data-parallel types (simd)

Implementation status

Feature	Status
P1928R15 std::simd — merge data-parallel types from the Parallelism TS 2	done (exceptions see below)
P3430R3 simd issues: explicit, unsequenced, identity-element position, and members of disabled simd	done
P3441R2 Rename simd_split to simd_chunk	done
P3287R3 Exploration of namespaces for std::simd	done
P2933R4 Extend ⟨bit⟩ header function with overloads for std::simd	done
P2663R7 Interleaved complex values support in std::simd	not started

Missing features

• simd<std::float16_t> is currently disabled / not implemented

Build, install, use?

This implementation is not intended for use yet. Nevertheless, it should be usable for experimenting. There is very simple build system support for installation via:

make prefix=~/.local install

But you can also just point your compiler's include path to this repository instead.

Build your own project with C++26 (latest GCC, PRs to support Clang are welcome). Just include <simd> and you're good to go:

#include <simd>

To build the tests there are multiple targets available. make help will list all of them.

Optional/exploratory features:

-D SIMD_IS_A_RANGE=1

If you turn this on you get an implementation of P3480 which makes simd and simd_mask read-only random-access ranges.

-D RANGES_TO_SIMD=1

std::array{1, 2, 3} | std::ranges::to<dp::basic_simd>() works without this, and constructs a simd<int, 3>. However, ranges without static extent and non-contiguous ranges are not supported without this feature.

Enables any_rg | std::ranges::to<dp::simd<T, N>>(). Precondition: std::ranges::size(any_rg) is equal to N.

-D IFNDR_SIMD_PRECONDITIONS=0

This implementation will render you program ill-formed if it can detect a potential precondition violation. This is not conforming, but maybe it should be?

The default on precondition violation otherwise is hard UB, which you can detect reliably with UBsan. You can change that to a 'trap' if _GLIBCXX_HARDEN is >= 3, or to a more verbose assertion failure by defining _GLIBCXX_ASSERTIONS.

-D SIMD_HAS_SUBSCRIPT_GATHER=1

Adds a subscript operator to basic_simd with integral basic_simd argument. The operator provides a permute/gather operation.

-D SIMD_CONCEPTS=0

This implementation defines several concepts in the std::datapar namespace with the same names, but extended to data-parallel types, as corresponding concepts from std. That's non-conforming and can be disabled.

-D SIMD_STD_BYTE=0

This implementation enables std::byte as vectorizable type. As this is not conforming, you can disable it.