What is the fastest portable way to copy an array in C++

Question

This question has been bothering me for some time. The possibilities I am considering are

1. memcpy
2. std::copy
3. cblas_dcopy

Does a

Answer 1

I've made a small benchmark (VS 2018 Preview, MKL 2017 Update 4) to compare memcpy and the sequential version of cblas_?copy and found them to be equally fast on float and double.