Struct secuencial

struct.cc

#include <functional>
#include <numeric>
#include <omp.h>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <vector>
#include <chrono>
#include <random>

const int N = 5000, REP = 4000;

std::default_random_engine generator(N * REP);
std::uniform_int_distribution<int> distribution(0, 9);
auto rng = std::bind(distribution, generator);

struct S { 
    int a, b;
    S(): a(rng()), b(rng()) {}
} s[N];

int main(){
    int R[REP];
    
    auto start = std::chrono::high_resolution_clock::now();
    for (int ii = 0; ii < REP; ++ii){
        int X1, X2;
        
        for (int i = 0; i < N; ++i)
            X1 = 2 * s[i].a + ii;
        
        for (int i = 0; i < N; i++)
            X2 = 3 * s[i].b - ii;
        
        if (X1 < X2)
            R[ii] = X1;
        else
            R[ii] = X2;
    }
    auto stop = std::chrono::high_resolution_clock::now();
    
    std::cout << "tiempo: " << 
        std::chrono::duration_cast<std::chrono::nanoseconds>(stop - 
        start).count()  << std::endl;
    
    return std::accumulate(R, R + REP, 0);
}