optimized memcpy

Optimization expert Agner Fog has published optimized memory functions: http://agner.org/optimize/#asmlib. It's under GPL though.

Some time ago Agner said that these functions should replace GCC builtins because they're a lot faster. I don't know if it's been done since then.

First, a word of advice. Assume that the people who wrote your standard library are not stupid. If there was a faster way to implement a general memcpy, they'd have done it.

Second, yes, there are better alternatives.

• In C++, use the std::copy function. It does the same thing, but it is 1) safer, and 2) potentially faster in some cases. It is a template, meaning that it can be specialized for specific types, making it potentially faster than the general C memcpy.
• Or, you can use your superior knowledge of your specific situation. The implementers of memcpy had to write it so it performed well in every case. If you have specific information about the situation where you need it, you might be able to write a faster version. For example, how much memory do you need to copy? How is it aligned? That might allow you to write a more efficient memcpy for this specific case. But it won't be as good in most other cases (if it'll work at all)

Unlikely. Your compiler/standard library will likely have a very efficient and tailored implementation of memcpy. And memcpy is basically the lowest api there is for copying one part of memory to another.

If you want further speedups, find a way to not need any memory copying.