試驗條件相同

我做一個函數的兩個版本的基準來篩選鏈表，一個是接收謂詞函數作爲參數，並在其中的謂語使用「宏模板」構建到函數中。我希望第一個運行速度更慢，因爲它在每次迭代中都會進行函數調用，但在我的盒子上它們的速度大致相同。關於爲什麼會發生這種情況的任何線索？任何幫助表示讚賞。試驗條件相同

下面是代碼：

#include <stdio.h> 
#include <stdlib.h> 
#include <sys/time.h> 

struct list_t { 
    int val; 
    struct list_t *next; 
}; 
typedef struct list_t list_t; 

// Removes elements not matching the predicate. 
// NOTE: This is not freeing the removed elements. 

list_t *keep(int (*predfun)(int,int), int predarg, list_t *list) { 
    list_t *this, *prev; 

    for (this=list, prev=NULL; this; prev=this, this=this->next) { 
     if (!predfun(this->val, predarg)) { 
      if (!prev) { 
       list = this->next; 
      } 
      else { 
       prev->next = this->next; 
      } 
     } 
    } 

    return list; 
} 

int less(int a, int b) { 
    return a<b; 
} 

// A "template" macro for the keep function. 
// The idea is to embed the predicate into the function, so that we 
// don't have to make a function call on each iteration. 

#define build_keep(test) {           \ 
    list_t *this, *prev;            \ 
                    \ 
    for (this=list, prev=NULL; this; prev=this, this=this->next) { \ 
     if (!(test)) {            \ 
      if (!prev) {            \ 
       list = this->next;         \ 
      }              \ 
      else {             \ 
       prev->next = this->next;        \ 
      }              \ 
     }               \ 
    }                \ 
    return list;              \ 
} 


list_t *keep_less(int arg, list_t *list) { 
    build_keep(this->val < arg); 
} 

#define LEN 1000000 
#define MOD 1024 

// Creates a new list. 
list_t *buildlist() { 
    int i; 
    list_t *list, *last, *t; 
    list=NULL, last=NULL; 
    srand(0); // Using always the same seed for the benchmark. 
    for (i=0; i<LEN; i++) { 
     if (!last) { 
      last = malloc(sizeof(list_t)); 
      list = last; 
     } 
     else { 
      last->next = malloc(sizeof(list_t)); 
      last = last->next; 
     } 
     last->val = rand() % MOD; 
    } 
    last->next = NULL; 
    return list; 
}  

int main() { 
    struct timeval t0, t1; 
    list_t *list, *t; 

    // With macro. 
    list = buildlist(); 
    //for (t=list; t; t=t->next) printf("%d ", t->val); printf("\n"); 
    gettimeofday(&t0, NULL); 
    keep_less(500, list); 
    gettimeofday(&t1, NULL); 
    printf("keep_less: %lf\n", (1000000 * (t1.tv_sec - t0.tv_sec) + (t1.tv_usec - t0.tv_usec))/1000000.0); 
    //for (t=list; t; t=t->next) printf("%d ", t->val); printf("\n"); 

    printf("\n"); 

    // Without macro. 
    list = buildlist(); 
    //for (t=list; t; t=t->next) printf("%d ", t->val); printf("\n"); 
    gettimeofday(&t0, NULL); 
    keep(less, 500, list); 
    gettimeofday(&t1, NULL); 
    printf("keep: %lf\n", (1000000 * (t1.tv_sec - t0.tv_sec) + (t1.tv_usec - t0.tv_usec))/1000000.0); 
    //for (t=list; t; t=t->next) printf("%d ", t->val); printf("\n"); 

    return 0; 
}

輸出這裏：