beating time

[Paul Lansky]

Can someone tell me why the following short program keeps such lousy
time? (metronome emulator)  I tried it under Ultrix 1.1 and 4.2.
I would expect some granularity but not to the extent I saw.  With an
argument of 1, for example, there are sometimes errors of as much as 50%
/* beats time according to command line argument */
#include <sys/time.h>
#include <sys/signal.h>
#include <stdio.h>
 
float tick,tval=0;
struct itimerval *value;
 
main(argc,argv)
char *argv[];
{
     int beatit();
     char *malloc();
     double atof();
 
     tick = atof(*++argv);
     value = (struct itimerval *)malloc(sizeof(value));
     value->it_value.tv_sec = value->it_interval.tv_sec = (int)tick;
     value->it_value.tv_usec = value->it_interval.tv_usec = (int)(
          1000000. * (tick - (float)value->it_value.tv_sec));
     (void) signal(SIGALRM,beatit);
     setitimer(ITIMER_REAL,value,value);
     while(1);
}
beatit() {
     getitimer(ITIMER_REAL,value);
     tval += value->it_value.tv_sec + (float)value->it_value.tv_usec/1000000;
     printf("%f"\n",tval);
}
thanks
Paul Lansky                bitnet == d0430 at pucc
Music Department           uucp   == princeton!winnie!paul
Princeton University