c - 应该更慢，但更快。为什么？

Question

好吧，让我解释一下这一点。在数组 SL[] 中，我得到了指向列表的指针(我可以说列表被分成了小部分)。所以我去 SL[0] 探索列表，然后去 SL[1] 探索列表......

typedef struct TSL {
   struct TSL *next;
   int a;
} LSL;

LSL* SL[n] = {0}; // Array of pointers ;)

// Loop 1
void Find_All_Arc_SL()
{
   int i;
   LSL *tmp;
   for(i=0;i<n;i++)
   {
      tmp = SL[i];
      while(tmp != 0)
      {
         //printf("I find arc! %d -> %d",i,tmp->a);
         tmp = tmp -> next;
      }
   }
}

循环 2。

typedef struct TAL {
   struct TAL *next;
   int v;
   int a;
 } LAL;
LAL *AL = 0;

void Find_All_Arc_AL()
{

  LAL *tmp;
  tmp = AL;

  while(tmp != 0)
  {
    //printf("I find arc %d -> %d \n",tmp->v,tmp->a);
    tmp = tmp -> next;
  };

}

在这个函数中，我只是探索列表...只需在没有任何数组等的情况下进行即可。

我的问题是:为什么 Find_All_Arc_SL() 总是比 Find_All_Arc_AL() 更快(毫秒)？这些函数的工作原理几乎相同，但第一个(更快的函数)必须做额外的工作

您要求提供完整代码。这是:你可以增加/减少n

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#define n 5500

//Define struct
typedef struct TSL {
   struct TSL *next;
   int a;
 } LSL;


typedef struct TAL {
   struct TAL *next;
   int v;
   int a;
 } LAL;


// Poiner and array of pointers
LAL *AL = 0;
LSL* SL[n] = {0};

// To Calculate time
__int64 freq, start, end, diff;


// Build graph
void Create_AL()
{

    LAL *tmp;
    int p,k;

 for(p=0;p<n;p++)
 for(k=0;k<n;k++)
 {
     // Add arc
    tmp = malloc (sizeof(LAL));
    tmp->v = p;
    tmp->a = k;

     if(AL == 0) { tmp->next = 0; AL = tmp; }
     else { tmp->next = AL; AL = tmp; }  
 }
}

// Find arc
void Find_All_Arc_AL()
{

    LAL *tmp;
    tmp = AL;

    while(tmp != 0)
    {
     //printf("I found arc %d -> %d \n",tmp->v,tmp->a);
     tmp = tmp -> next;
    };

}


// Build graph
void Create_SL()
{

    LSL *tmp;
    int p,k;

 for(p=0;p<n;p++)
 for(k=0;k<n;k++)
 { 
    // Add arc
    tmp = malloc(sizeof(LSL));
    tmp -> a = k;       

    if(SL[p] == 0) {  tmp -> next = 0; SL[p] = tmp; }
    else { tmp -> next = SL[p]; SL[p] = tmp; }
    }

}


void Find_All_Arc_SL()
{

 int i;
    LSL *tmp;


    for(i=0;i<n;i++)
    {
    tmp = SL[i];

        while(tmp != 0)
        {
        //printf("I find arc %d -> %d \n", i, tmp->a);
        tmp = tmp -> next;
        }

    }

}


/**
 ** CALCULATE TIME!
 **/

void start_timer()
{
 freq = 0; start = 0; end = 0; diff = 0;

    QueryPerformanceFrequency((LARGE_INTEGER*)&freq);
 QueryPerformanceCounter((LARGE_INTEGER*)&start);

}

void end_timer()
{

    QueryPerformanceCounter((LARGE_INTEGER*)&end);
    diff = ((end - start) * 1000) / freq;

}

int main(int argc, char *argv[])
{

Create_SL();

start_timer();
 Find_All_Arc_SL();
end_timer();
printf("Find_All_Arc_SL SEARCHING ALL ARC TOOK %d \n",diff);



 Create_AL();

start_timer();
 Find_All_Arc_AL();
end_timer();
printf("Find_All_Arc_AL SEARCHING ALL ARC TOOK %d \n",diff);



  system("PAUSE");  
  return 0;
}

Answer 1

这取决于您的数据。您应该发布一个完整的(工作)示例。

另外，你是如何测量时间的？您确定比较有意义吗？