1 files changed, 224 insertions, 0 deletions
diff --git a/library/std/src/sys/windows/time.rs b/library/std/src/sys/windows/time.rs
new file mode 100644
index 000000000..b8209a854
--- /dev/null
+++ b/library/std/src/sys/windows/time.rs
@@ -0,0 +1,224 @@
+use crate::cmp::Ordering;
+use crate::fmt;
+use crate::mem;
+use crate::sys::c;
+use crate::sys_common::IntoInner;
+use crate::time::Duration;
+
+use core::hash::{Hash, Hasher};
+
+const NANOS_PER_SEC: u64 = 1_000_000_000;
+const INTERVALS_PER_SEC: u64 = NANOS_PER_SEC / 100;
+
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Hash)]
+pub struct Instant {
+    // This duration is relative to an arbitrary microsecond epoch
+    // from the winapi QueryPerformanceCounter function.
+    t: Duration,
+}
+
+#[derive(Copy, Clone)]
+pub struct SystemTime {
+    t: c::FILETIME,
+}
+
+const INTERVALS_TO_UNIX_EPOCH: u64 = 11_644_473_600 * INTERVALS_PER_SEC;
+
+pub const UNIX_EPOCH: SystemTime = SystemTime {
+    t: c::FILETIME {
+        dwLowDateTime: INTERVALS_TO_UNIX_EPOCH as u32,
+        dwHighDateTime: (INTERVALS_TO_UNIX_EPOCH >> 32) as u32,
+    },
+};
+
+impl Instant {
+    pub fn now() -> Instant {
+        // High precision timing on windows operates in "Performance Counter"
+        // units, as returned by the WINAPI QueryPerformanceCounter function.
+        // These relate to seconds by a factor of QueryPerformanceFrequency.
+        // In order to keep unit conversions out of normal interval math, we
+        // measure in QPC units and immediately convert to nanoseconds.
+        perf_counter::PerformanceCounterInstant::now().into()
+    }
+
+    pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
+        // On windows there's a threshold below which we consider two timestamps
+        // equivalent due to measurement error. For more details + doc link,
+        // check the docs on epsilon.
+        let epsilon = perf_counter::PerformanceCounterInstant::epsilon();
+        if other.t > self.t && other.t - self.t <= epsilon {
+            Some(Duration::new(0, 0))
+        } else {
+            self.t.checked_sub(other.t)
+        }
+    }
+
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant { t: self.t.checked_add(*other)? })
+    }
+
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant { t: self.t.checked_sub(*other)? })
+    }
+}
+
+impl SystemTime {
+    pub fn now() -> SystemTime {
+        unsafe {
+            let mut t: SystemTime = mem::zeroed();
+            c::GetSystemTimePreciseAsFileTime(&mut t.t);
+            t
+        }
+    }
+
+    fn from_intervals(intervals: i64) -> SystemTime {
+        SystemTime {
+            t: c::FILETIME {
+                dwLowDateTime: intervals as c::DWORD,
+                dwHighDateTime: (intervals >> 32) as c::DWORD,
+            },
+        }
+    }
+
+    fn intervals(&self) -> i64 {
+        (self.t.dwLowDateTime as i64) | ((self.t.dwHighDateTime as i64) << 32)
+    }
+
+    pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
+        let me = self.intervals();
+        let other = other.intervals();
+        if me >= other {
+            Ok(intervals2dur((me - other) as u64))
+        } else {
+            Err(intervals2dur((other - me) as u64))
+        }
+    }
+
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
+        let intervals = self.intervals().checked_add(checked_dur2intervals(other)?)?;
+        Some(SystemTime::from_intervals(intervals))
+    }
+
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        let intervals = self.intervals().checked_sub(checked_dur2intervals(other)?)?;
+        Some(SystemTime::from_intervals(intervals))
+    }
+}
+
+impl PartialEq for SystemTime {
+    fn eq(&self, other: &SystemTime) -> bool {
+        self.intervals() == other.intervals()
+    }
+}
+
+impl Eq for SystemTime {}
+
+impl PartialOrd for SystemTime {
+    fn partial_cmp(&self, other: &SystemTime) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for SystemTime {
+    fn cmp(&self, other: &SystemTime) -> Ordering {
+        self.intervals().cmp(&other.intervals())
+    }
+}
+
+impl fmt::Debug for SystemTime {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SystemTime").field("intervals", &self.intervals()).finish()
+    }
+}
+
+impl From<c::FILETIME> for SystemTime {
+    fn from(t: c::FILETIME) -> SystemTime {
+        SystemTime { t }
+    }
+}
+
+impl IntoInner<c::FILETIME> for SystemTime {
+    fn into_inner(self) -> c::FILETIME {
+        self.t
+    }
+}
+
+impl Hash for SystemTime {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.intervals().hash(state)
+    }
+}
+
+fn checked_dur2intervals(dur: &Duration) -> Option<i64> {
+    dur.as_secs()
+        .checked_mul(INTERVALS_PER_SEC)?
+        .checked_add(dur.subsec_nanos() as u64 / 100)?
+        .try_into()
+        .ok()
+}
+
+fn intervals2dur(intervals: u64) -> Duration {
+    Duration::new(intervals / INTERVALS_PER_SEC, ((intervals % INTERVALS_PER_SEC) * 100) as u32)
+}
+
+mod perf_counter {
+    use super::NANOS_PER_SEC;
+    use crate::sync::atomic::{AtomicU64, Ordering};
+    use crate::sys::c;
+    use crate::sys::cvt;
+    use crate::sys_common::mul_div_u64;
+    use crate::time::Duration;
+
+    pub struct PerformanceCounterInstant {
+        ts: c::LARGE_INTEGER,
+    }
+    impl PerformanceCounterInstant {
+        pub fn now() -> Self {
+            Self { ts: query() }
+        }
+
+        // Per microsoft docs, the margin of error for cross-thread time comparisons
+        // using QueryPerformanceCounter is 1 "tick" -- defined as 1/frequency().
+        // Reference: https://docs.microsoft.com/en-us/windows/desktop/SysInfo
+        //                   /acquiring-high-resolution-time-stamps
+        pub fn epsilon() -> Duration {
+            let epsilon = NANOS_PER_SEC / (frequency() as u64);
+            Duration::from_nanos(epsilon)
+        }
+    }
+    impl From<PerformanceCounterInstant> for super::Instant {
+        fn from(other: PerformanceCounterInstant) -> Self {
+            let freq = frequency() as u64;
+            let instant_nsec = mul_div_u64(other.ts as u64, NANOS_PER_SEC, freq);
+            Self { t: Duration::from_nanos(instant_nsec) }
+        }
+    }
+
+    fn frequency() -> c::LARGE_INTEGER {
+        // Either the cached result of `QueryPerformanceFrequency` or `0` for
+        // uninitialized. Storing this as a single `AtomicU64` allows us to use
+        // `Relaxed` operations, as we are only interested in the effects on a
+        // single memory location.
+        static FREQUENCY: AtomicU64 = AtomicU64::new(0);
+
+        let cached = FREQUENCY.load(Ordering::Relaxed);
+        // If a previous thread has filled in this global state, use that.
+        if cached != 0 {
+            return cached as c::LARGE_INTEGER;
+        }
+        // ... otherwise learn for ourselves ...
+        let mut frequency = 0;
+        unsafe {
+            cvt(c::QueryPerformanceFrequency(&mut frequency)).unwrap();
+        }
+
+        FREQUENCY.store(frequency as u64, Ordering::Relaxed);
+        frequency
+    }
+
+    fn query() -> c::LARGE_INTEGER {
+        let mut qpc_value: c::LARGE_INTEGER = 0;
+        cvt(unsafe { c::QueryPerformanceCounter(&mut qpc_value) }).unwrap();
+        qpc_value
+    }
+}