让代码跑得更快试验

看到文章https://blog.csdn.net/qq_34827674/article/details/109147330，写程序试验了一下。

1. 提升数据缓存的命中率（遍历二维数组），好像是正确的。

2. 提升指令缓存的命中率（循环遍历数组，把小于 50 的数组元素置为 0；将数组排序），不知道什么原因，试验结果没有提升速度。

程序如下：

#include "stdio.h"
#include <time.h>
#include <sys/time.h>
#include <algorithm>
using namespace std;

#define N 1000
#define N1 10000

int main(void)
{
    struct timeval tpstart;
    struct timeval tpend;
    
    int array[N][N];
    int i,j;
    
    
    gettimeofday(&tpstart,NULL);
    for(i=0; i < N; i++)
    {
       for(j=0; j < N; j++)
       {
         array[i][j] = 1;
       }
    }
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);

    gettimeofday(&tpstart,NULL);
    for(i=0; i < N; i++)
    {
       for(j=0; j < N; j++)
       {
         array[j][i] = 1;
       }
    }
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);
    
    gettimeofday(&tpstart,NULL);
    for(i=0; i < N; i++)
    {
       for(j=0; j < N; j++)
       {
         array[i][j] = 1;
       }
    }
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);

    gettimeofday(&tpstart,NULL);
    for(i=0; i < N; i++)
    {
       for(j=0; j < N; j++)
       {
         array[i][j] = 1;
       }
    }
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);
    
    
    int array1[N1];
    printf("\n");
    for(i=0; i<N1; i++)
    {
      array1[i]=rand()%100;
      //printf("%d ",array1[i]);
    }
    printf("\n");
    
    gettimeofday(&tpstart,NULL);
    for(i=0; i<N1; i++)
    {
      if(array1[i]<50)
      {
        array1[i]=0;
      }
    }    
    sort(array1,array1+N1);
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);
    //printf("\n");
    //for(i=0; i<N1; i++)
    //{
      //printf("%d ",array1[i]);
    //}
    //printf("\n");

    
    printf("\n");
    for(i=0; i<N1; i++)
    {
      array1[i]=rand()%100;
      //printf("%d ",array1[i]);
    }
    printf("\n");
    
    gettimeofday(&tpstart,NULL);
    sort(array1,array1+N1);
    for(i=0; i<N1; i++)
    {
      if(array1[i]<50)
      {
        array1[i]=0;
      }
    }    
    gettimeofday(&tpend,NULL);
    printf("time:%lds,%ldms\n", tpend.tv_sec-tpstart.tv_sec, tpend.tv_usec-tpstart.tv_usec);
    //for(i=0; i<N1; i++)
    //{
      //printf("%d ",array1[i]);
    //}
    //printf("\n");
    
    
    return 0;
    
}

用g++编译运行，结果：

第一次

time:0s,21539ms
time:0s,93967ms
time:0s,16531ms
time:0s,16554ms


time:0s,6204ms


time:0s,6070ms

第二次

time:0s,21348ms
time:0s,94609ms
time:0s,16356ms
time:0s,16607ms


time:0s,6203ms


time:0s,6081ms