Sieve method prime generator

From , 3 Years ago, written in C, viewed 194 times.

/*筛法素数产生器
语法：result=prime(int a[],int n);
参数：
a[]：  用于返回素数的数组
n：    产生n以内的素数，按升序放入a[]中
返回值：    n以内素数的个数
注意：
        其中W[],B[]已知，W[i]>0且W[i]与W[j]互质, 求a
*/
 
int prime ( int a[],int n )
{
        int i,j,k,x,num,*b;
        n++;
        n/=2;
        b= ( int * ) malloc ( sizeof ( int ) * ( n+1 ) *2 );
        a[0]=2;
        a[1]=3;
        num=2;
        for ( i=1; i<=2*n; i++ )
                b[i]=0;
        for ( i=3; i<=n; i+=3 )
                for ( j=0; j<2; j++ )
                {
                        x=2* ( i+j )-1;
                        while ( b[x]==0 )
                        {
                                a[num++]=x;
                                for ( k=x; k<=2*n; k+=x )
                                        b[k]=1;
                        }
                }
        return num;
}
 

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Sieve method prime generator

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