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

int main (int argc, char *argv[])
{
   if(argc!=2)
   {
      printf("Error: ./tlb <num_pages>\n");
      return -1;
   }
   int NUMPAGES = atoi(argv[1]); //number of pages to load
   int PAGESIZE=sysconf(_SC_PAGESIZE); //page size in the system
   /*
   We keep the number of iterations constant so that the program does not run for too long, but it is long enough for the time measures to be relevant.
   */
   long unsigned NUM_ITER = (unsigned)(1024*1024*256)/NUMPAGES;
   long unsigned i,j; // iterators
   long unsigned msz; // matrix size
   clock_t a,b; //time measurements
   double avg=0.0; // time calc
   //Jump size to access different pages in each load
   int jump = PAGESIZE/sizeof(int);
   msz=NUMPAGES*jump;
   int *array;
   array = malloc(msz*sizeof(int));

   if (NUMPAGES < 0)
   {
      printf("Error, the number of pages should be positive\n");
      return -1;
   }

   srand((int)clock());

   int n=0;
   //Measure 4 times to improve the results quality (although not enough)
   for(n=0; n<4; n++)
   {
      a=clock();
      /*
      The process is executed several times to reduce the error of the clock measurement (it would lack precision otherwise). First lap will always miss in the TLB. If the number of pages is low, we may have some hits in the TLB in the later laps.
      */
      for(i=0; i<NUM_ITER; i++)
      {
         //We load the matrix without accessing the same page consecutively
         for(j=0;j<NUMPAGES*jump;j+=jump)
         {
            array[j]=rand()%1024;
         }
      }
      b =clock()-a; //Time to load the array NUM_ITER times
      //Aprox. time to do one operation (ignoring the loop)
      avg+=(b*1.0)/(NUMPAGES*NUM_ITER*1.0);
   }
   avg=avg/4.0;
   printf("%d pages, Average time: %10.2fns\n",NUMPAGES,1000000000*avg/
	(double)CLOCKS_PER_SEC); //value in nanoseconds
   return 0;
}