/* 
   iobasic.c
   
   Demonstrates the effect of the memory hierarchy and the limitations
   of the RAM model. 

   The RAM model assumes that all memory accesses take the same and
   defines

   complexity = CPU complexity =  nb. CPU operations  

   When working with large data the cache and IO behaviour (nb. cache
   misses/page faults) are relevant and may actually be dominant.
   Theoretically this is modeled by

   cache complexity = nb blocks transferred between cache and main
   memory

   IO complexity = nb blocks transferred between main memory and disk  
 */
#include <stdio.h> 
#include <time.h> 
#include <assert.h> 
#include <stdlib.h> 

#define PRINT if(0)

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

  clock_t  t1, t2; 
  if (argc !=2)  {
    printf("usage: %s [n]\n", argv[0]);
    exit(1); 
  }
  long n = atol(argv[1]); 
  printf("n=%ld (%.1f G) ints which require  %.1f GB RAM\n", 
	 n, 
	 (float)n/(1<<30), 
	 (float)n*sizeof(int)/(1<<30)); 


  //allocate  and initialize
  t1 = clock(); 
  printf("%30s", "allocate and initialize a: "); 
  int* a = (int*)malloc(n * sizeof(int)); 
  assert(a); 
  for (long i=0; i<n; i++) {
    a[i]=i; 
  } 
  t2 = clock(); 
  printf("time elapsed %.3f seconds\n", (double)(t2-t1)/CLOCKS_PER_SEC); 
  

  //SEQUENTIAL ACCESS ARRAY A
  int sum = 0; 
  t1 = clock(); 
  printf("%30s", "sequential access: "); 
  printf("\n");
  for (long i=0; i<n; i++)  {
    sum =(sum + a[i])%2; 
    
    //print % progress
    PRINT {if (i% (n/100) ==0) printf("%d %% ", (int) (i/(n/100))); fflush(stdout);}
  }
  t2 = clock(); 
  printf("\n%30s time elapsed %.3f seconds\n", " ", (double)(t2-t1)/CLOCKS_PER_SEC); 


  //RANDOM ACCESS ARRAY A
  t1 = clock(); 
  printf("%30s", "random access: "); 
  printf("\n");
  for (long i=0; i<n; i++) {
    //generate a random index in 0..n
    long  k = random() % n; 
    sum =(sum + a[i])%2; 
  
    //print % progress
    PRINT  { if (i% (n/100) ==0) printf("%d %% ", (int) (i/(n/100)));fflush(stdout);}
  } 
  t2 = clock(); 
  printf("\n%30s time elapsed %.3f seconds\n"," ",  (double)(t2-t1)/CLOCKS_PER_SEC); 
  
  return 0; 
}