On Sat, Sep 12, 2026 at 08:34:29PM +0800, Yuao Ma wrote:
> Thanks for the quick review! On second thought, I agree that the
> initial implementation wasn't fully vectorized. The current <simd>
> actually provides support similar to your generic vector approach.
> Instead of the shl/shr operations in the current patch, we could do
> the following:
Yeah, with whatever details Matthias/Jonathan want in there.
> template<__simd_integral _VX, __simd_integral _VS>
> requires (_VX::size() == _VS::size())
> && (sizeof(typename _VX::value_type) == sizeof(typename
> _VS::value_type))
> [[__gnu__::__always_inline__]]
> constexpr _VX
> shl(const _VX& __v, const _VS& __s0) noexcept
> {
> using _Tp = typename _VX::value_type;
> using _Sp = typename _VS::value_type;
> constexpr int _Nd = sizeof(_Tp) * __CHAR_BIT__;
> const rebind_t<_Sp, _VX> __s(__s0);
> const _VX __sl(__s & _Sp(_Nd - 1));
> _VX __r = select(__s < _Sp(_Nd), __v << __sl, _VX());
> if constexpr (is_signed_v<_Sp>)
> {
> const _VX __sr = -__sl & _Tp(_Nd - 1);
> if constexpr (is_signed_v<_Tp>)
> __r = select(__s < _Sp(0),
> select(__s > _Sp(-_Nd), __v >> __sr, __v >> (_Nd -
> 1)), __r);
> else
> __r = select(__s < _Sp(0), select(__s > _Sp(-_Nd), __v >> __sr,
> _VX()), __r);
Just note these lines are too long. And for the first case, it might be
better then to
__r = select(__s < _Sp(0),
__v >> select(__s > _Sp(-Nd), __sr, _Sp(_Nd - 1)),
__r);
or
__r = select(__s < _Sp(0), __v >> min(-__s, _Sp(_Nd - 1)), __r);
Jakub
