/* fibtimeV.c
 *
 * Neal Nelson  2009.11.04
 *
 * Set the virtual interval timer to 0.1 and then repeatedly accumulate its
 * value from the sighandler handler on each 0.1 sec interrupt.
 * Use the timer to see how long fib(n) takes in virtual time.
 *
 * Usage: ./a.out fibnum
 *
 *
 */

#include <stdio.h>
#include <unistd.h>     /* for pause() */
#include <stdlib.h>
#include <sys/time.h>
#include <signal.h>

/* Prototypes must occur before sig handlers are referenced */
static void itimer_handler(int);
unsigned long fib(unsigned int n);

/* Initialize the virtual time accumulator */
static long virt_count = 0;

main(int argc, char *argv[])
{ int i;
  unsigned long thefib;

  struct itimerval virt;

  if (argc != 2) 
  { printf("usage:  ./a.out fibnum\n");
    exit(-1);
  }

  /* Register the itimer_handler to catch SIGALRM, SIGVTALRM, SIGPROF */

  if (signal(SIGVTALRM, itimer_handler) == SIG_ERR)
    printf("Parent: Unable to create handler for SIGVTALRM\n");

  /* Initialize the virtual itimers to one tenth of a second*/
  virt.it_interval.tv_sec = 0;
  virt.it_interval.tv_usec = 99999;
  virt.it_value.tv_sec = 0;
  virt.it_value.tv_usec = 99999;


  setitimer(ITIMER_VIRTUAL, &virt, NULL);
  /* thefib = fib(40); */
  thefib = fib(atoi(argv[1])); 
  printf("fib: %ld virt_count: %ld\n", thefib, virt_count);
}


static void itimer_handler(int signo)
{
  switch(signo)
  { case SIGVTALRM:
      virt_count++;
      printf("Parent: received SIGVTALRM signal, virt_count: %ld\n",virt_count);
      break;
    default: break; /* should never get here */
  }
  return; 
}

unsigned long fib(unsigned int n)
{ if (n == 0) return 0;
  else if (n == 1 || n == 2) return 1;
  else return (fib(n-1) + fib(n-2));
}