Sigma calculation in naive approach

sigma_calculation_naive.cpp

#include <iostream>
#include <vector>
#include <math.h>

using namespace std;

#define READ(x) freopen(x, "r", stdin)
#define WRITE(x) freopen(x, "w", stdout)

#define PB push_back

typedef unsigned long long ULL;
typedef vector<int> VI;

#define MAX_PRIME 10000000
#define MAX 10000000

ULL bitFlag[MAX_PRIME / 64 + 7];
VI primes;
uint t[MAX + 7];
ULL sigma[MAX + 7];

void sieveBitwise() {
    for (int i = 3; i*i <= MAX_PRIME; i += 2) {
        if ((bitFlag[i/64] & (1LL << (i%64))) == 0) {
            for (ULL j = i*i; j <= MAX_PRIME; j += 2*i) {
                bitFlag[(j/64)] |= (1L << (j%64));
            }
        }
    }
    primes.PB(2);
    for (ULL i = 3; i <= MAX_PRIME; i += 2)
        if ((bitFlag[i/64] & (1L << (i%64))) == 0) primes.PB(i);
}

uint countDivisors(ULL n) {
    if(n == 0) return 0;
    uint ret = 1, root = (int)sqrt((double)n);
    for(int i=0; primes[i] <= root; i++) {
        int power = 0;
        while(!(n % primes[i])) { n /= primes[i]; power++; }
        if(power > 0) ret *= (power + 1);
    }
    if(n > 1) ret *= 2;
    return ret;
}

ULL sumDivisors(ULL n) {
    if(n == 0) return 0;
    ULL ret = 1, root = (int)sqrt((double)n);
    for(int i=0; primes[i] <= root; i++) {
        int pi = primes[i];
        ULL tmp = pi;
        while(!(n % pi)) { n /= pi; tmp *= pi; }
        if(tmp > pi) ret *= (tmp - 1) / (pi - 1);
    }
    if(n > 1) ret *= (n*n - 1) / (n - 1);
    return ret;
}

void preCal() {
    for (int i = 1; i <= MAX; ++i) {
        t[i] = countDivisors(i);
        sigma[i] = sumDivisors(i);
    }
}

int main() {
    WRITE("output.txt");

    double cl = clock();

    sieveBitwise();
    preCal();

    for (int i = 1; i <= 30; ++i) {
        printf("%d: %lu %llu\n", i, t[i], sigma[i]);
    }

    cl = clock() - cl;
    fprintf(stderr, "Total Execution Time = %lf seconds\n", cl / CLOCKS_PER_SEC);
}