这是一个适当的循环优化 [英] Is this a proper for-loop optimization

问题描述

为了做家庭作业，我需要优化一个循环，在7.5秒内运行。我想我可能已经这样做了，因为我的代码在4秒内运行。不过，我担心我做得不对，因为我的老师告诉我们，7.5秒以下的事情可能是错误的。所以我担心我可能不会正确地做事。这里是原始代码：

  #include< stdio.h> 
 #include< stdlib.h> 
 
 #define N_TIMES 600000 $ b $ #define ARRAY_SIZE 10000 
 $ b $ int main（void）
 {
 double * array = calloc（ARRAY_SIZE，的sizeof（双））; 
 double sum = 0; 
 int i; 
 
 for（i = 0; i  
 int j; （j = 0; j  sum + = array [j]; 
 
; 
} 
} 
 
 return 0; 
 
 $ / code $ 
 
 
这里是我的优化：
 $ b $ （i = 0; i  
 int j; b 
  （j = 0; j  sum + = array [j] + array [j + 1] + array [j + 2] + array [j + 3] + array [j + 4] + array [j + 5] + array [j + 6] + array [j + 7] + array [ ]。 
 sum1 + = array [j + 10] + array [j + 11] + array [j + 12] + array [j + 13] + array [j + 14] + array [j + 15] + array [j + 16] + array [j + 17] + array [j + 18] + array [j + 19]; 
} 
 
} 
 sum + = sum1; 
  
这些算术运算的数目是否相同？我是否改变了代码，或者我只是优化？
解决方案
您的优化是不正确的：
 $ b （j = 0; j  ）的
 $ b 
  pre> 
 
 
您现在循环内循环的次数是您应该循环的次数的一半。
 
For a homework assignment I need to optimize a loop to run in under 7.5 seconds. I think I may have done this because my code runs in 4 seconds. However, I am worried I am not doing it correctly because my instructor told us that anything too far under 7.5 seconds is probably wrong. So I am worried that I might not be doing things correctly. Here is the original code:
#include <stdio.h>
#include <stdlib.h>

#define N_TIMES     600000
#define ARRAY_SIZE   10000

int main (void)
{
    double  *array = calloc(ARRAY_SIZE, sizeof(double));
    double  sum = 0;
    int     i;

    for (i = 0; i < N_TIMES; i++) {

        int     j;

        for (j = 0; j < ARRAY_SIZE; j++) {
            sum += array[j];
            }
        }

    return 0;
}
Here is my optimization:
   for (i = 0; i < N_TIMES; i++) {

        int     j;

        for (j = 0; j < ARRAY_SIZE/2; j += 20) {
            sum += array[j] + array[j+1] + array[j+2] + array[j+3] + array[j+4] + array[j+5] + array[j+6] + array[j+7] + array[j+8] + array[j+9];
            sum1 += array[j+10] + array[j+11] + array[j+12] + array[j+13] + array[j+14] + array[j+15] + array[j+16] + array[j+17] + array[j+18] + array[j+19];
            }

        }
    sum += sum1;
Are these doing the same number of arithmetic operations? Did I change the code somehow or am I just optimizing well?
解决方案
Your optimizations are not correct:
for (j = 0; j < ARRAY_SIZE/2; j += 20) {
You now loop half as many times in the inner loop as you should.

                        
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