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

#define MAX_SENDERS 64
#define MAXINT 2147483647.0

/* Buffer strategy: shared or partitioned */
/* #define SHARED 1  */

/* #define DEBUG 1 */
/* #define RAND_DEBUG 1 */

int main()
{
  int n;
  int inpkt[MAX_SENDERS];
  int outputq[MAX_SENDERS];
  int pktssent[MAX_SENDERS];
  int pktslost[MAX_SENDERS];
  int totpktssent, totpktslost;
  int totalq;
  int maxqsize;
  int steps;
  int i,j;
  int pktsthistime;
  int randint;
  float lambda;
  float prob;
  int dest;

  printf("N? ");
  scanf("%d", &n);

  printf("Number of buffers for each output queue? ");
  scanf("%d", &maxqsize);
#ifdef SHARED
  maxqsize *= n;
#endif

  printf("Traffic load level? (lambda) ");
  scanf("%f", &lambda);

  printf("Simulation time length? ");
  scanf("%d", &steps);

  /* Initialization */
  for( j = 0; j < n; j++ )
    {
      pktssent[j] = 0;
      pktslost[j] = 0;
      inpkt[j] = 0;
      outputq[j] = 0;
    }
  totalq = 0;
  totpktssent = 0;
  totpktslost = 0;

  srandom(time(NULL));

  /* Main loop: repeat once for each time step interval being simulated */

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

      /* Transmit one packet on each output link (if non-empty queue there) */
      for( j = 0; j < n; j++ )
	{
	  if( outputq[j] > 0 )
	    {
	      outputq[j]--;
	      totalq--;
	    }
	}
#ifdef DEBUG
      printf("Total output queue at time step %d: %d\n", i, totalq);
      printf("Output queue info after transmission, before new arrivals...\n");
      for( j = 0; j < n; j++ )
	{
	  printf("%2d ", outputq[j]);
	}
      printf("\n");
#endif

      /* Generate the new packet arrivals in time step i */
      pktsthistime = 0;
      for( j = 0; j < n; j++ )
	{
	  /* Generate a packet (at random) from each input link */
	  randint = random();
	  prob = randint / MAXINT;
#ifdef RAND_DEBUG
	  printf("randfloat for pkt generation is %f\n", prob);
#endif
	  if( prob <= lambda )
	    inpkt[j] = 1;
	  else inpkt[j] = 0;
	  if( inpkt[j] > 0 )
	    {
	      pktsthistime++;
	      pktssent[j]++;
	      totpktssent++;

	      /* Generate a destination for each packet, uniform distribution */
	      randint = random();
	      prob = randint / MAXINT;
#ifdef RAND_DEBUG
	      printf("randfloat for destination is %f\n", prob);
#endif
	      dest = prob * n + 1;
	      inpkt[j] = dest;
	    }
	}
#ifdef DEBUG
      printf("There were %d new packets generated in round %d\n", pktsthistime, i);
      printf("Destination info for those packets: ");
      for( j = 0; j < n; j++ )
	{
	  if( inpkt[j] == 0 )
	    printf(" - ");
	  else printf("%2d ", inpkt[j]);
	}
      printf("\n");
#endif

      /* Move each new packet onto its appropriate output queue */
      for( j = 0; j < n; j++ )
	{
	  if( inpkt[j] == 0 )
	    continue;
	  dest = inpkt[j] - 1;
	  /* Check for packet loss */
#ifdef SHARED
	  /* completely shared buffers */
	  if( totalq < maxqsize )
#else
	  /* completely partitioned buffers */
	  if( outputq[dest] < maxqsize )
#endif
	    {
	      outputq[dest]++;
	      totalq++;
	    }
	  else
	    {
	      pktslost[dest]++;
	      totpktslost++;
	    }
	}
#ifdef DEBUG
      printf("Total output queue for step %d: %d\n", i, totalq);
      printf("Output queue info after arrivals and tossing...\n");
      for( j = 0; j < n; j++ )
	{
	  printf("%2d ", outputq[j]);
	}
      printf("\n");
      printf("Cumulative toss information to date, by output link...\n");
      for( j = 0; j < n; j++ )
	{
	  printf("%2d ", pktslost[j]);
	}
      printf("\n");
#endif

    }

  /* Print simulation results */
  printf("\n\nSimulation run length: %d time steps\n", steps);
  printf("NxN switch, with N = %d\n", n);
  printf("Total packets generated: %d\n", totpktssent);
  printf("      By input link: ");
  for( j = 0; j < n; j++ )
    {
      printf("%2d ", pktssent[j]);
    }
  printf("\n");
  printf("Total packets lost: %d (%10.8f)\n",
	 totpktslost, (float) 1.0 * totpktslost/totpktssent);
  printf("      By output link: ");
  for( j = 0; j < n; j++ )
    {
      printf("%2d ", pktslost[j]);
    }
  printf("\n");
}