teste_vol_6thelement.cpp

#include <iostream>
#include <iterator>
#include <random>
#include <set>
#include <sys/time.h>
#include <vector>

using namespace std;

static inline uint64_t startRDTSC (void) {
    unsigned cycles_low, cycles_high;
    asm volatile ("CPUID\n\t"
            "RDTSC\n\t"
            "mov %%edx, %0\n\t"
            "mov %%eax, %1\n\t": "=r" (cycles_high), "=r" (cycles_low)::
            "%rax", "%rbx", "%rcx", "%rdx");
    return (static_cast<uint64_t>(cycles_high) << 32) | cycles_low;
}

static inline uint64_t stopRDTSCP (void) {
    unsigned cycles_low, cycles_high;
    asm volatile("RDTSCP\n\t"
            "mov %%edx, %0\n\t"
            "mov %%eax, %1\n\t"
            "CPUID\n\t": "=r" (cycles_high), "=r" (cycles_low):: "%rax",
            "%rbx", "%rcx", "%rdx");
    return (static_cast<uint64_t>(cycles_high) << 32) | cycles_low;
}

class CPUBenchmark {
public:
    CPUBenchmark() :
        ticktime(0) {
        start();
    }
    
    uint64_t ticktime;

    void start() {
        ticktime = startRDTSC();
    }

    uint64_t stop() {
        return stopRDTSCP() - ticktime;

    }
};

int sexto_maior_copia(const vector<int>& vec)
{
    //cópia para um set que já é ordenado e tem elementos unicos
    set<int> buffer (vec.begin(), vec.end()); 
    auto it = buffer.rbegin();
    advance(it, 5);
    return *it;
}

int sexto_maior_iter(const vector<int>& vec)
{   // Aqui iterando 6 vezes e cada vez pegando um
    // máximo[i] < máximo[i+1]
    int currMax=0;
    for (unsigned j=0; j<vec.size();++j) {
        if (vec[j] > currMax) {currMax = vec[j];}
    }
    
    for (unsigned i=0; i<5; ++i) {
        int m = 0;
        for (unsigned j=0; j<vec.size();++j) {
            if (vec[j] > m && vec[j] < currMax) {
                m = vec[j];               
            }
        }
        currMax = m;
    }
    return currMax;    
}

int main()
{
    random_device seeder;
    mt19937 engine(seeder());
    uniform_int_distribution<int> dist(0, 20);
    
    // Cria um vector com 20 elementos aleatórios
    vector<int> original;
    original.reserve(20);
    for (unsigned i=0; i<20; ++i) {
        original.emplace_back(dist(engine));
    }
       
    cout << "Vetor original: " << '{';
    for (unsigned i=0; i<original.size(); ++i) {
        cout << original[i];
        cout << (i == original.size()-1 ? '}':',');
    }
    
    cout << endl << endl << "Teste em ciclos de CPU" << endl << endl;
    CPUBenchmark time;
    time.start();
    cout << "Sexto maior elemento (cópia): " << sexto_maior_copia(original) << endl;
    cout << "CiclosCPU: " << (time.stop()*1.0) << endl << endl;
    
    time.start();
    cout << "Sexto maior elemento (iter) : " << sexto_maior_iter(original) << endl;
    cout << "CiclosCPU: " << (time.stop()*1.0) << endl << endl;
    return 0;
}