A simple sieve in Phobos?

[Chris Williams]

On Tuesday, 18 March 2014 at 14:23:32 UTC, bearophile wrote:
> There is a efficient Sieve implementation in C++ here:
>
> http://code.activestate.com/recipes/577966-even-faster-prime-generator/?in=lang-cpp
>
> There are of course far faster implementations, but its 
> performance is not bad, while being still simple and quite 
> short.

Here's a straightforward implementation, if you don't already 
have one (I assume you're doing this for Rosetta Code). I had to 
decrease your MAX_N by 100-fold to get a similar runtime, but 
it's a fairly faithful implementation of Eratosthenes' method as 
written.

enum uint MAX_N = 10_000_000U;

void calcPrimes() pure nothrow {
     uint[][uint] markers;

     for (uint L = 2; L < MAX_N; L++) {
         uint[]* pList = (L in markers);
         if (pList is null) {
             markers[L + L] = [L];
         }
         else {
             uint[] list = *pList;
             size_t len = list.length - 1;
             for (uint L2 = 0; L2 < len; L2++) {
                 uint val = list[L2];
                 markers[ L + val ] ~= val;
             }

             // reuse the current list for the last item to save 
allocations
             list[0] = list[len];
             list.length = 1;
             markers[ L + list[len] ] = list;
         }
     }
}

void main() {
     calcPrimes;
}