diff --git a/library/std/src/time.rs b/library/std/src/time.rs index 3d09824019e3a..1805d8926098d 100644 --- a/library/std/src/time.rs +++ b/library/std/src/time.rs @@ -682,6 +682,56 @@ impl SystemTime { pub fn checked_sub(&self, duration: Duration) -> Option { self.0.checked_sub_duration(&duration).map(SystemTime) } + + /// Saturating [`SystemTime`] addition, computing `self + duration`, + /// returning [`SystemTime::MAX`] if overflow occurred. + /// + /// In the case that the `duration` is smaller than the time precision of + /// the operating system, `self` will be returned. + #[unstable(feature = "time_saturating_systemtime", issue = "151199")] + pub fn saturating_add(&self, duration: Duration) -> SystemTime { + self.checked_add(duration).unwrap_or(SystemTime::MAX) + } + + /// Saturating [`SystemTime`] subtraction, computing `self - duration`, + /// returning [`SystemTime::MIN`] if overflow occurred. + /// + /// In the case that the `duration` is smaller than the time precision of + /// the operating system, `self` will be returned. + #[unstable(feature = "time_saturating_systemtime", issue = "151199")] + pub fn saturating_sub(&self, duration: Duration) -> SystemTime { + self.checked_sub(duration).unwrap_or(SystemTime::MIN) + } + + /// Saturating computation of time elapsed from an earlier point in time, + /// returning [`Duration::ZERO`] in the case that `earlier` is later or + /// equal to `self`. + /// + /// # Examples + /// + /// ```no_run + /// #![feature(time_saturating_systemtime)] + /// use std::time::{Duration, SystemTime}; + /// + /// let now = SystemTime::now(); + /// let prev = now.saturating_sub(Duration::new(1, 0)); + /// + /// // now - prev should return non-zero. + /// assert_eq!(now.saturating_duration_since(prev), Duration::new(1, 0)); + /// assert!(now.duration_since(prev).is_ok()); + /// + /// // prev - now should return zero (and fail with the non-saturating). + /// assert_eq!(prev.saturating_duration_since(now), Duration::ZERO); + /// assert!(prev.duration_since(now).is_err()); + /// + /// // now - now should return zero (and work with the non-saturating). + /// assert_eq!(now.saturating_duration_since(now), Duration::ZERO); + /// assert!(now.duration_since(now).is_ok()); + /// ``` + #[unstable(feature = "time_saturating_systemtime", issue = "151199")] + pub fn saturating_duration_since(&self, earlier: SystemTime) -> Duration { + self.duration_since(earlier).unwrap_or(Duration::ZERO) + } } #[stable(feature = "time2", since = "1.8.0")] diff --git a/library/std/tests/time.rs b/library/std/tests/time.rs index 0ef89bb09c637..b73e7bc3962eb 100644 --- a/library/std/tests/time.rs +++ b/library/std/tests/time.rs @@ -1,5 +1,6 @@ #![feature(duration_constants)] #![feature(time_systemtime_limits)] +#![feature(time_saturating_systemtime)] use std::fmt::Debug; use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH}; @@ -269,3 +270,41 @@ fn system_time_max_min() { assert!(SystemTime::MIN.checked_add(MIN_INTERVAL).is_some()); assert!(SystemTime::MIN.checked_sub(MIN_INTERVAL).is_none()); } + +#[test] +fn system_time_saturating() { + // Perform saturating addition on SystemTime::MAX to see how it behaves. + assert_eq!(SystemTime::MAX.saturating_add(Duration::ZERO), SystemTime::MAX); + assert_eq!(SystemTime::MAX.saturating_add(Duration::new(1, 0)), SystemTime::MAX); + assert!(SystemTime::MAX.checked_add(Duration::new(1, 0)).is_none()); + assert_eq!( + SystemTime::MAX.saturating_sub(Duration::new(1, 0)), + SystemTime::MAX.checked_sub(Duration::new(1, 0)).unwrap() + ); + + // Perform saturating subtraction on SystemTime::MIn to see how it behaves. + assert_eq!(SystemTime::MIN.saturating_sub(Duration::ZERO), SystemTime::MIN); + assert_eq!(SystemTime::MIN.saturating_sub(Duration::new(1, 0)), SystemTime::MIN); + assert!(SystemTime::MIN.checked_sub(Duration::new(1, 0)).is_none()); + assert_eq!( + SystemTime::MIN.saturating_add(Duration::new(1, 0)), + SystemTime::MIN.checked_add(Duration::new(1, 0)).unwrap() + ); + + // Check saturating_duration_since with various constant values. + assert!(SystemTime::MAX.saturating_duration_since(SystemTime::MIN) >= Duration::ZERO); + assert_eq!(SystemTime::MAX.saturating_duration_since(SystemTime::MAX), Duration::ZERO); + assert!(SystemTime::MAX.duration_since(SystemTime::MAX).is_ok()); + assert_eq!(SystemTime::MIN.saturating_duration_since(SystemTime::MAX), Duration::ZERO); + assert!(SystemTime::MIN.duration_since(SystemTime::MAX).is_err()); + assert_eq!( + (SystemTime::UNIX_EPOCH + Duration::new(1, 0)) + .saturating_duration_since(SystemTime::UNIX_EPOCH), + Duration::new(1, 0) + ); + assert_eq!( + SystemTime::UNIX_EPOCH + .saturating_duration_since(SystemTime::UNIX_EPOCH + Duration::new(1, 0)), + Duration::ZERO + ); +}