State of “memset” functionality in C++ with modern compilers

Question

Context:

A while ago, I stumbled upon this 2001 DDJ article by Alexandrescu: http://www.ddj.com/cpp/184403799

It\'s about comparing various ways to initialize

Answer 1

Memset/memcpy are mostly written with a basic instruction set in mind, and so can be outperformed by specialized SSE routines, which on the other hand enforce certain alignment constraints.

But to reduce it to a list :

1. For data-sets <= several hundred kilobytes memcpy/memset perform faster than anything you could mock up.
2. For data-sets > megabytes use a combination of memcpy/memset to get the alignment and then use your own SSE optimized routines/fallback to optimized routines from Intel etc.
3. Enforce the alignment at the start up and use your own SSE-routines.

This list only comes into play for things where you need the performance. Too small/or once initialized data-sets are not worth the hassle.

Here is an implementation of memcpy from AMD, I can't find the article which described the concept behind the code.