Why is `std::copy` 5x (!) slower than `memcpy` for reading one int from a char buffer, in my test program?

Question

This is a follow-up to this question where I posted this program:

#include 
#include 
#include 
#include 

        

Answer 1

That is not the results I get:

> g++ -O3 XX.cpp 
> ./a.out
cast:      5 ms
memcpy:    4 ms
std::copy: 3 ms
(counter:  1264720400)

Hardware: 2GHz Intel Core i7
Memory:   8G 1333 MHz DDR3
OS:       Max OS X 10.7.5
Compiler: i686-apple-darwin11-llvm-g++-4.2 (GCC) 4.2.1

On a Linux box I get different results:

> g++ -std=c++0x -O3 XX.cpp 
> ./a.out 
cast:      3 ms
memcpy:    4 ms
std::copy: 21 ms
(counter:  731359744)


Hardware:  Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz
Memory:    61363780 kB
OS:        Linux ip-10-58-154-83 3.2.0-29-virtual #46-Ubuntu SMP
Compiler:  g++ (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3