replace size_t i=0 by size_t i(0)

[GregorDeCillia]

While testing, i found that replacing

for( size_t i=0 ; i < dim ; ++i )

by

for( size_t i(0) ; i < dim ; ++i )

in array_algebra.hpp gives a better performance for the state types boost::array and std::array.

I also replaced these loops on other parts of the code just in case there are similar performance impacts.

[ddemidov]

Interesting. The following two code snippets result in identical assembler code (obtained with g++ -S). I wonder where the speedup comes from.

1.

#include <stddef.h>
int main() {
    int j = 0;
    for (size_t i(0); i < 10; ++i) ++j;
}

2.

#include <stddef.h>
int main() {
    int j = 0;
    for (size_t i = 0; i < 10; ++i) ++j;
}

[GregorDeCillia]

I was also kind of suprised that these changes made a difference. My tests used g++ with the Ofast flag as well as the boost_unit_test framework.

[mariomulansky]

Indeed quite surprising. You would think that this wouldnt make any difference to the compiler compiler...

May I ask how much of a performance improvement this gives? I would like to also check on the intel compiler before doing this merge.

[GregorDeCillia]

srange. i just created a simpler test case and created two assembly files one with and one without my commit and there does not seem to be any difference.

i guess i should have done more testing before creating a pull request. thanks for pointing that out @ddemidov

@mariomulansky please close this pull request. there is probably a problem with my test case