ex4_array.c

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

#define SIZE 100000000

#define GET_SEC(a, b)  ((b - a) / (double)CLOCKS_PER_SEC)  

int main(int argc, char** argv)
{
   clock_t start;
   double* x = malloc(SIZE * sizeof(*x));
   double  sum;
   
   for(int i = 0; i < SIZE; i++)
      x[i] = i + 1.0;
   
   sum = 0.0; start = clock();

   /* In order 1 */
   for(int i = 0; i < SIZE; i++)
      sum += x[i];

   printf("IO time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);

   sum = 0.0; start = clock();

   /* In order 2 */
   for(int k = 0; k < 100; k++)
      for(int i = 0; i < SIZE / 100; i++)
         sum += x[k * (SIZE / 100) + i];

   printf("O1 time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);

   sum = 0.0; start = clock();
   
   for(int i = 0; i < SIZE / 100; i++)
      for(int k = 0; k < 100; k++)
         sum += x[k * (SIZE / 100) + i];

   printf("OH time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);

   sum = 0.0; start = clock();
   
   for(int i = 0; i < SIZE / 1000; i++)
      for(int k = 0; k < 1000; k++)
         sum += x[k * (SIZE / 1000) + i];

   printf("OT time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);

   sum = 0.0; start = clock();
   
   for(int i = 0; i < SIZE / 10000; i++)
      for(int k = 0; k < 10000; k++)
         sum += x[k * (SIZE / 10000) + i];

   printf("Ot time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);

   sum = 0.0; start = clock();
   
   for(int i = 0; i < SIZE / 100000; i++)
      for(int k = 0; k < 100000; k++)
         sum += x[k * (SIZE / 100000) + i];

   printf("Oh time=%.3f sum=%.1f\n", GET_SEC(start, clock()), sum);
}