era2e.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define ST unsigned long
#define SW (sizeof(ST) * 8) 

// 5 7 . 11 13 .  17 19 . 23 25 . 29 31 . 35 37 . 41 43 . 47 49 . 53 55 . 59 61 . 65 67 . 71 73 . 77 79 . 
//
//

void doSieve(ST max, void (*action)(ST)){

    ST *sieve = calloc(((max) / (2 * SW)) + 3, sizeof(ST)); 

    ST i;
    if(action) action(3);
    for(i = 0; i < ((max) ) / 3; ++i) 
    { 
        // printf(" i = %lu, p = %lu, %lu \n", i, p, i/SW);
        if(!(sieve[i / SW] & ((ST)1 << (i % SW)))) 
        { 
            ST p = 5 + 2*(i + i/2);

            if(p > max){
               break;
            }
            ST j = (p*p-5)/2 - (p*p-5)/6;

            // printf(" l_0: %lu  %lu %lu / %lu\n", p, p*p, j, p%3);
            ST k;
            if(p%3 == 1){
                k = ((p+4)*p-5)/2 - (((p+4)*p-5)/2)/3;
            }
            else{
                k = ((p+2)*p-5)/2 - (((p+2)*p-5)/2)/3;
            }

            // printf(" k = %lu max/3 = %lu max/3-k = %lu \n", k, max/3, max/3-k);
            if(max/3 > j){
                if(max/3 < k){
                    // only one half step
                    sieve[(j) / SW] |= ((ST)1 << ((j) % SW)); 
                    continue;
                }
                ST l=0;

                for(l=0; l <= (max/3-k)/(2*p); l++){
                    // printf("p %lu unsetting %lu %lu,  / %lu / %lu\n", p, j+2*l*p, k+2*l*p, max/3, k);
                    sieve[(j+2*l*p) / SW] |= ((ST)1 << ((j+2*l*p) % SW)); 
                    sieve[(k+2*l*p) / SW] |= ((ST)1 << ((k+2*l*p) % SW)); 
                    // printf(" k = %lu 2pl+k = %lu max/3 = %lu max/3-k = %lu \n", k, 2*p*l + k, max/3, max/3-k);
                }
                
                if(j + 2*l+p <= max/3){
                    sieve[(j+2*l*p) / SW] |= ((ST)1 << ((j+2*l*p) % SW)); 
                }
            }
            if(action) action(p);
        } 
    }
}

    void modPrint(ST p){
        static long anz = 0;
        anz++;
        if(anz % 1000 == 7) printf("%lu %lu\n", anz, p);
        /*
        static long anz = 0;
        anz++;
        if(anz % 1000 == 7) printf("%lu %lu\n", anz, p);
        */
    }

int main(){
    // unsigned long max = 10000000UL;
    unsigned long max = 10000000UL;
    // unsigned long max = 500UL;

    // doSieve(max*log(max)*log(log(max)) , &modPrint);
    doSieve((max * log(max) + max * (log(log(max)) - 0.9385)), &modPrint);
    printf("max = %lu\n", (max * log(max) + max * (log(log(max)) - 0.9385)));
    // check(13);

    return 0;
}