text: #ifndef __SSI_TIMER_H__
  #define __SSI_TIMER_H__
  
  #include <sys/time.h>
  
  #define DTYPE float
  
  extern struct timeval start_time[3];
  extern float elapse[3];
  #define timer_on(id) gettimeofday (&start_time[id], NULL)
  #define timer_off(id) 	\
  		{	\
  		     struct timeval result, now; \
  		     gettimeofday (&now, NULL);  \
  		     timeval_subtract(&result, &now, &start_time[id]);	\
  		     elapse[id] += result.tv_sec+ (DTYPE) (result.tv_usec)/1000000.;	\
  		}
  
  #define timer_msg(id, msg) \
  	printf("%f seconds elapsed in %s\n", (DTYPE)(elapse[id]), msg);  \
  
  #define timer_reset(id) elapse[id] = 0
  
  /* Subtract the `struct timeval' values X and Y,
     storing the result in RESULT.
     Return 1 if the difference is negative, otherwise 0.  */
  
  inline int
  timeval_subtract (struct timeval *result, struct timeval *x, struct timeval *y)
  {
    /* Perform the carry for the later subtraction by updating y. */
    if (x->tv_usec < y->tv_usec) {
      int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
      y->tv_usec -= 1000000 * nsec;
      y->tv_sec += nsec;
    }
    if (x->tv_usec - y->tv_usec > 1000000) {
      int nsec = (y->tv_usec - x->tv_usec) / 1000000;
      y->tv_usec += 1000000 * nsec;
      y->tv_sec -= nsec;
    }
  
    /* Compute the time remaining to wait.
       tv_usec is certainly positive. */
    result->tv_sec = x->tv_sec - y->tv_sec;
    result->tv_usec = x->tv_usec - y->tv_usec;
  
    /* Return 1 if result is negative. */
    return x->tv_sec < y->tv_sec;
  }
  
  #endif
  