Function fbclock_gettime_tz

fbclock/fbclock.c:479–513

    fbclock_truetime* truetime,
    int time_standard) {
  int64_t phc_time_ns = state->phc_time_ns;
  if (state->ingress_time_ns > phc_time_ns) {
    return FBCLOCK_E_PHC_IN_THE_PAST;
  }
  int64_t diff_ns = sysclock_time_now_ns - state->sysclock_time_ns;
  // Refuse to extrapolate past a sane bound, or backwards in time. Either case
  // means the daemon stopped updating shared memory or there's a clock-source
  // mismatch, so the extrapolated PHC time would have unbounded error.
  if (diff_ns < 0 || diff_ns > FBCLOCK_MAX_EXTRAPOLATION_NS) {
    return FBCLOCK_E_DATA_STALE;
  }
  // NANOSECONDS_IN_SECONDS is uint64_t, which would otherwise convert the
  // signed dividend to unsigned. When coef_ppb is negative the product is
  // negative, and that conversion turns it into a value near 2^64, making
  // the quotient ~2^64/1e9 ≈ 18.45 s instead of the intended small ns count.
  phc_time_ns +=
      diff_ns + diff_ns * state->coef_ppb / (int64_t)NANOSECONDS_IN_SECONDS;

  // Time since the last SYNC from the GM, at the PHC instant this call
  // reports. Clamped like the past_v2 path below: a coef_ppb under -1e9
  // extrapolates back past ingress, and fbclock_window_of_uncertainty casts
  // the holdover product to uint64_t.
  int64_t holdover_ns = phc_time_ns - state->ingress_time_ns;
  double seconds =
      holdover_ns > 0 ? (double)holdover_ns / NANOSECONDS_IN_SECONDS : 0.0;

  // UTC offset applied if time standard used is UTC (and not TAI)
  if (time_standard == FBCLOCK_UTC) {
    phc_time_ns = fbclock_apply_utc_offset_v2(state, phc_time_ns);
  }

  // calculate the Window of Uncertainty (WOU) (in nanoseconds)
  uint64_t wou_ns =
      fbclock_window_of_uncertainty(seconds, error_bound_ns, h_value_ns);
  truetime->earliest_ns = phc_time_ns - wou_ns;
  truetime->latest_ns = phc_time_ns + wou_ns;
  return FBCLOCK_E_NO_ERROR;
}