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I'm running an i7-6700k, on Windows 10 with the MSVC 2015 compiler, my results were 9592 primes between 0 and 100000 Time taken = 12.808 Without optimisations, and 9592 primes between 0 and 100000 Time taken = 10.853 with full optimisations. I would ahve thought it would have been much better. without and with optimisations.

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It is wasting a lot of time with the pointless bool assignments. See my post below.

But then I'm not running the same code as either the parent of my comment, or the article, and the benchmark doesn't hold. It's how fast can my CPU run the same code vs theres. I could make it faster again by precomputing a table and doing a lookup but that defies the point!

Very good point. I was just surprised how much that simple bool assignment slowed things down so massively.

I started at 10.853, and with very little effort brought it down to 0.003

The slowdown isn't in assigning the bool; If you pass in 10000000 into that function, it's going to get isPrime set to true on the first iteration, but if you early out, you save all of those values. Again, this isn't really the point of the exercise, it's supposed to be comparing the performance of the same piece of code ran on different hardware.

https://gist.github.com/anonymous/c6d5bae04334cbc7ef9583ebb7...

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