基于OpenMP的C++并行编程简单示例

示例要求：在整数A和B之间找到符合条件的值X，使f(X)=C。

示例代码（需要在VS中开启OpenMP支持）：

#include<iostream>
#include<time.h>
#include"omp.h"

int f(int i) {
    int i4_huge = 2147483647;
    int j;
    int k;
    int value;
    value = i;
    for (j = 1; j <= 5; j++)
    {
        k = value / 127773;
        value = 16807 * (value - k * 127773) - k * 2836;
        if (value <= 0)
        {
            value = value + i4_huge;
        }
    }
    return value;
}

int search(int a, int b, int c)
{
    int fi;
    int i;
    int j;

    j = -1;

    #pragma omp parallel for num_threads(6)
    for (i = a; i <= b; i++)
    {
        fi = f(i);
        if (fi == c)
        {
            j = i;
            break;
        }
    }

    return j;
}


int main()
{
    int j;
    int a = 1;
    int b = 10000000;
    int c = 45;
    double wtime;

    clock_t start, finish;
    double totaltime;
    start = clock();

    j = search(a, b, c);

    finish = clock();
    totaltime = (double)(finish - start) / CLOCKS_PER_SEC;
    std::cout << "
 search运行时间为" << totaltime << "秒！" << std::endl;
    system("pause");
    return 0;
}

并行算法的加速情况：

加速前：

加速后：