// returns result of function
static <A> A benchForNSeconds(double n, S desc default str(f), IF0<A> f) {
  benchForNSeconds(r { f! }, n);
  ret f!;
}

// returns minimal time needed
static long benchForNSeconds(S desc default str(r), Runnable r, double n) {
  long start = sysNow(), min = -1, print = sysNow();
  int seconds = 1;
  long count = 0, sum = 0;
  while (seconds <= n) {
    long time = nanos();
    r.run();
    ++count;
    time = nanos()-time;
    min = min < 0 ? time : min(min, time);
    sum += time;
    double avg = doubleRatio(sum, count);
    if (sysNow() >= start+seconds*1000) {
      printAndSetConsoleTitleIfMain(
        "n=" + n2(count) + ", avg=" + formatDouble(nanosToMS(avg), 3) + " ms, " +
        "min=" + formatDouble(nanosToMS(min), 3) + " ms: " +
        desc + " (" + seconds + "/" + n + " s, last=" + formatDouble(nanosToMS(time), 3) + " ms, " + n2(count) + "/s)");
      ++seconds;
      count = sum = 0;
    }
  }
  ret min;
}