[Shootout-list] nsieve g++ c++

[Daniel Skiles]

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> The elements initially contain random stuff, not all "0" (or all
> "false" in this case). I'm not sure that this is actually a problem
> for your program, though, maybe you initialize all explicitely
> somewhere.

I initialize all of the values to boolean true in the nsieve function.
 I've attached a copy of a version with a proper delete[] to this
message.

> I'd just use vector<bool> and avoid this completely :-)

That's a really good idea.  I'll start working on that.

Thanks,
Daniel

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#include <cstdlib>
#include <iostream>

using namespace std;

int nsieve(int, bool[]);

int main(int argc, char *argv[])
{
    int n =3D (argc =3D=3D 2) ? atoi(argv[1]) : 2;
    int m;
    bool* flags;
   =20
    m =3D (1<<n)*10000;
    flags =3D new bool[m];
    cout << "Primes up to " << m << " " << nsieve(m, flags) << endl;
    delete[] flags;
    flags =3D NULL;
   =20
    m =3D (1<<n-1)*10000;
    flags =3D new bool[m];
    cout << "Primes up to " << m << " " << nsieve(m, flags) << endl;
    delete[] flags;
    flags =3D NULL;
   =20
    m =3D (1<<n-2)*10000;
    flags =3D new bool[m];
    cout << "Primes up to " << m << " " << nsieve(m, flags) << endl;
    delete[] flags;
    flags =3D NULL;
   =20
    return EXIT_SUCCESS;
}

int nsieve(int m, bool *isPrime)
{
    int count =3D 0;
   =20
    for (int i=3D2; i<=3Dm; i++)
        isPrime[i] =3D true;
       =20
    for(int i=3D2; i<=3Dm; i++){
        if(isPrime[i]){
            for(int k=3Di*2; k<=3Dm; k+=3Di){
                isPrime[k] =3D false;
            }
            count++;
        }
    }
    return count;
}


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