cpp_playground/misc/likely.cpp

#include <algorithm>
#include <iostream>
#include <sys/time.h>

#define likely(x) __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)

using namespace std;
const int SIZE = 128 * 1024 * 1024;
const int RANGE = RAND_MAX / 2;

int arr[SIZE];

void func1(int *pval)
{
    int big = 0, small = 0;
    timeval start, end;
    gettimeofday(&start, nullptr);
    for (int idx = 0; idx < SIZE; idx++)
    {
        if (((pval[idx]) > RANGE / 2))
            big++;
        else
            small++;
    }
    gettimeofday(&end, nullptr);
    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
    cout << __func__ << " duration: " << usec << ", big: " << big << ", small:" << small << endl;
}

void func2(int *pval)
{
    int big = 0, small = 0;
    timeval start, end;
    gettimeofday(&start, nullptr);
    for (int idx = 0; idx < SIZE; idx++)
    {
        if (((pval[idx]) <= RANGE / 2))
            small++;
        else
            big++;
    }
    gettimeofday(&end, nullptr);
    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
    cout << __func__ << " duration: " << usec << ", big: " << big << ", small:" << small << endl;
}

void func_likely(int *pval)
{
    int big = 0, small = 0;
    timeval start, end;
    gettimeofday(&start, nullptr);
    for (int idx = 0; idx < SIZE; idx++)
    {
        if (likely((pval[idx]) > RANGE / 2))
            big++;
        else
            small++;
    }
    gettimeofday(&end, nullptr);
    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
    cout << __func__ << " duration: " << usec << ", big: " << big << ", small:" << small << endl;
}

void func_unlikely(int *pval)
{
    int big = 0, small = 0;
    timeval start, end;
    gettimeofday(&start, nullptr);
    for (int idx = 0; idx < SIZE; idx++)
    {
        if (unlikely((pval[idx]) > RANGE / 2))
            big++;
        else
            small++;
    }

    gettimeofday(&end, nullptr);
    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
    cout << __func__ << " duration: " << usec << ", big: " << big << ", small:" << small << endl;
}

int main()
{
    srand(time(nullptr));
    for (int i = 0; i < SIZE; i++)
    {
        arr[i] = (rand() % (RANGE + 1));
    }
    cout << "random dataset:" << endl;
    func1(arr);
    func2(arr);
    func_likely(arr);
    func_unlikely(arr);
    sort(arr, arr + SIZE);
    cout << "sorted dataset:" << endl;
    func1(arr);
    func2(arr);
    func_likely(arr);
    func_unlikely(arr);
}