29.10.8.5 basic_vec exposition only conditional operators [simd.cond]
friend constexpr basic_vec
simd-select-impl(const mask_type& mask, const basic_vec& a, const basic_vec& b) noexcept;
Returns: A
basic_vec object where the
ith element equals
mask[i] ? a[i] : b[i] for all
i in the range of
[
0, size())
.