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    // Copyright 2012-2017 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use iter::Sum;
    use ops::{Add, Sub, Mul, Div, AddAssign, SubAssign, MulAssign, DivAssign};

    const NANOS_PER_SEC: u32 = 1_000_000_000;
    const NANOS_PER_MILLI: u32 = 1_000_000;
    const NANOS_PER_MICRO: u32 = 1_000;
    const MILLIS_PER_SEC: u64 = 1_000;
    const MICROS_PER_SEC: u64 = 1_000_000;

    /// A `Duration` type to represent a span of time, typically used for system
    /// timeouts.
    ///
    /// Each `Duration` is composed of a whole number of seconds and a fractional part
    /// represented in nanoseconds.  If the underlying system does not support
    /// nanosecond-level precision, APIs binding a system timeout will typically round up
    /// the number of nanoseconds.
    ///
    /// `Duration`s implement many common traits, including [`Add`], [`Sub`], and other
    /// [`ops`] traits.
    ///
    /// [`Add`]: ../../std/ops/trait.Add.html
    /// [`Sub`]: ../../std/ops/trait.Sub.html
    /// [`ops`]: ../../std/ops/index.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::time::Duration;
    ///
    /// let five_seconds = Duration::new(5, 0);
    /// let five_seconds_and_five_nanos = five_seconds + Duration::new(0, 5);
    ///
    /// assert_eq!(five_seconds_and_five_nanos.as_secs(), 5);
    /// assert_eq!(five_seconds_and_five_nanos.subsec_nanos(), 5);
    ///
    /// let ten_millis = Duration::from_millis(10);
    /// ```
    #[stable(feature = "duration", since = "1.3.0")]
    #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash, Default)]
    pub struct Duration {
        secs: u64,
        nanos: u32, // Always 0 <= nanos < NANOS_PER_SEC
    }

    impl Duration {
        /// Creates a new `Duration` from the specified number of whole seconds and
        /// additional nanoseconds.
        ///
        /// If the number of nanoseconds is greater than 1 billion (the number of
        /// nanoseconds in a second), then it will carry over into the seconds provided.
        ///
        /// # Panics
        ///
        /// This constructor will panic if the carry from the nanoseconds overflows
        /// the seconds counter.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let five_seconds = Duration::new(5, 0);
        /// ```
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn new(secs: u64, nanos: u32) -> Duration {
            let secs = secs.checked_add((nanos / NANOS_PER_SEC) as u64)
                .expect("overflow in Duration::new");
            let nanos = nanos % NANOS_PER_SEC;
            Duration { secs: secs, nanos: nanos }
        }

        /// Creates a new `Duration` from the specified number of whole seconds.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_secs(5);
        ///
        /// assert_eq!(5, duration.as_secs());
        /// assert_eq!(0, duration.subsec_nanos());
        /// ```
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn from_secs(secs: u64) -> Duration {
            Duration { secs: secs, nanos: 0 }
        }

        /// Creates a new `Duration` from the specified number of milliseconds.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_millis(2569);
        ///
        /// assert_eq!(2, duration.as_secs());
        /// assert_eq!(569000000, duration.subsec_nanos());
        /// ```
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn from_millis(millis: u64) -> Duration {
            let secs = millis / MILLIS_PER_SEC;
            let nanos = ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI;
            Duration { secs: secs, nanos: nanos }
        }

        /// Creates a new `Duration` from the specified number of microseconds.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(duration_from_micros)]
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_micros(1_000_002);
        ///
        /// assert_eq!(1, duration.as_secs());
        /// assert_eq!(2000, duration.subsec_nanos());
        /// ```
        #[unstable(feature = "duration_from_micros", issue = "44400")]
        #[inline]
        pub fn from_micros(micros: u64) -> Duration {
            let secs = micros / MICROS_PER_SEC;
            let nanos = ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO;
            Duration { secs: secs, nanos: nanos }
        }

        /// Returns the number of _whole_ seconds contained by this `Duration`.
        ///
        /// The returned value does not include the fractional (nanosecond) part of the
        /// duration, which can be obtained using [`subsec_nanos`].
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::new(5, 730023852);
        /// assert_eq!(duration.as_secs(), 5);
        /// ```
        ///
        /// To determine the total number of seconds represented by the `Duration`,
        /// use `as_secs` in combination with [`subsec_nanos`]:
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::new(5, 730023852);
        ///
        /// assert_eq!(5.730023852,
        ///            duration.as_secs() as f64
        ///            + duration.subsec_nanos() as f64 * 1e-9);
        /// ```
        ///
        /// [`subsec_nanos`]: #method.subsec_nanos
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn as_secs(&self) -> u64 { self.secs }

        /// Returns the fractional part of this `Duration`, in nanoseconds.
        ///
        /// This method does **not** return the length of the duration when
        /// represented by nanoseconds. The returned number always represents a
        /// fractional portion of a second (i.e. it is less than one billion).
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_millis(5010);
        /// assert_eq!(duration.as_secs(), 5);
        /// assert_eq!(duration.subsec_nanos(), 10_000_000);
        /// ```
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn subsec_nanos(&self) -> u32 { self.nanos }

        /// Checked `Duration` addition. Computes `self + other`, returning [`None`]
        /// if overflow occurred.
        ///
        /// [`None`]: ../../std/option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)), Some(Duration::new(0, 1)));
        /// assert_eq!(Duration::new(1, 0).checked_add(Duration::new(std::u64::MAX, 0)), None);
        /// ```
        #[stable(feature = "duration_checked_ops", since = "1.16.0")]
        #[inline]
        pub fn checked_add(self, rhs: Duration) -> Option<Duration> {
            if let Some(mut secs) = self.secs.checked_add(rhs.secs) {
                let mut nanos = self.nanos + rhs.nanos;
                if nanos >= NANOS_PER_SEC {
                    nanos -= NANOS_PER_SEC;
                    if let Some(new_secs) = secs.checked_add(1) {
                        secs = new_secs;
                    } else {
                        return None;
                    }
                }
                debug_assert!(nanos < NANOS_PER_SEC);
                Some(Duration {
                    secs,
                    nanos,
                })
            } else {
                None
            }
        }

        /// Checked `Duration` subtraction. Computes `self - other`, returning [`None`]
        /// if the result would be negative or if underflow occurred.
        ///
        /// [`None`]: ../../std/option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::new(0, 1).checked_sub(Duration::new(0, 0)), Some(Duration::new(0, 1)));
        /// assert_eq!(Duration::new(0, 0).checked_sub(Duration::new(0, 1)), None);
        /// ```
        #[stable(feature = "duration_checked_ops", since = "1.16.0")]
        #[inline]
        pub fn checked_sub(self, rhs: Duration) -> Option<Duration> {
            if let Some(mut secs) = self.secs.checked_sub(rhs.secs) {
                let nanos = if self.nanos >= rhs.nanos {
                    self.nanos - rhs.nanos
                } else {
                    if let Some(sub_secs) = secs.checked_sub(1) {
                        secs = sub_secs;
                        self.nanos + NANOS_PER_SEC - rhs.nanos
                    } else {
                        return None;
                    }
                };
                debug_assert!(nanos < NANOS_PER_SEC);
                Some(Duration { secs: secs, nanos: nanos })
            } else {
                None
            }
        }

        /// Checked `Duration` multiplication. Computes `self * other`, returning
        /// [`None`] if overflow occurred.
        ///
        /// [`None`]: ../../std/option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::new(0, 500_000_001).checked_mul(2), Some(Duration::new(1, 2)));
        /// assert_eq!(Duration::new(std::u64::MAX - 1, 0).checked_mul(2), None);
        /// ```
        #[stable(feature = "duration_checked_ops", since = "1.16.0")]
        #[inline]
        pub fn checked_mul(self, rhs: u32) -> Option<Duration> {
            // Multiply nanoseconds as u64, because it cannot overflow that way.
            let total_nanos = self.nanos as u64 * rhs as u64;
            let extra_secs = total_nanos / (NANOS_PER_SEC as u64);
            let nanos = (total_nanos % (NANOS_PER_SEC as u64)) as u32;
            if let Some(secs) = self.secs
                .checked_mul(rhs as u64)
                .and_then(|s| s.checked_add(extra_secs)) {
                debug_assert!(nanos < NANOS_PER_SEC);
                Some(Duration {
                    secs,
                    nanos,
                })
            } else {
                None
            }
        }

        /// Checked `Duration` division. Computes `self / other`, returning [`None`]
        /// if `other == 0`.
        ///
        /// [`None`]: ../../std/option/enum.Option.html#variant.None
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
        /// assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
        /// assert_eq!(Duration::new(2, 0).checked_div(0), None);
        /// ```
        #[stable(feature = "duration_checked_ops", since = "1.16.0")]
        #[inline]
        pub fn checked_div(self, rhs: u32) -> Option<Duration> {
            if rhs != 0 {
                let secs = self.secs / (rhs as u64);
                let carry = self.secs - secs * (rhs as u64);
                let extra_nanos = carry * (NANOS_PER_SEC as u64) / (rhs as u64);
                let nanos = self.nanos / rhs + (extra_nanos as u32);
                debug_assert!(nanos < NANOS_PER_SEC);
                Some(Duration { secs: secs, nanos: nanos })
            } else {
                None
            }
        }
    }

    #[stable(feature = "duration", since = "1.3.0")]
    impl Add for Duration {
        type Output = Duration;

        fn add(self, rhs: Duration) -> Duration {
            self.checked_add(rhs).expect("overflow when adding durations")
        }
    }

    #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
    impl AddAssign for Duration {
        fn add_assign(&mut self, rhs: Duration) {
            *self = *self + rhs;
        }
    }

    #[stable(feature = "duration", since = "1.3.0")]
    impl Sub for Duration {
        type Output = Duration;

        fn sub(self, rhs: Duration) -> Duration {
            self.checked_sub(rhs).expect("overflow when subtracting durations")
        }
    }

    #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
    impl SubAssign for Duration {
        fn sub_assign(&mut self, rhs: Duration) {
            *self = *self - rhs;
        }
    }

    #[stable(feature = "duration", since = "1.3.0")]
    impl Mul<u32> for Duration {
        type Output = Duration;

        fn mul(self, rhs: u32) -> Duration {
            self.checked_mul(rhs).expect("overflow when multiplying duration by scalar")
        }
    }

    #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
    impl MulAssign<u32> for Duration {
        fn mul_assign(&mut self, rhs: u32) {
            *self = *self * rhs;
        }
    }

    #[stable(feature = "duration", since = "1.3.0")]
    impl Div<u32> for Duration {
        type Output = Duration;

        fn div(self, rhs: u32) -> Duration {
            self.checked_div(rhs).expect("divide by zero error when dividing duration by scalar")
        }
    }

    #[stable(feature = "time_augmented_assignment", since = "1.9.0")]
    impl DivAssign<u32> for Duration {
        fn div_assign(&mut self, rhs: u32) {
            *self = *self / rhs;
        }
    }

    #[stable(feature = "duration_sum", since = "1.16.0")]
    impl Sum for Duration {
        fn sum<I: Iterator<Item=Duration>>(iter: I) -> Duration {
            iter.fold(Duration::new(0, 0), |a, b| a + b)
        }
    }

    #[stable(feature = "duration_sum", since = "1.16.0")]
    impl<'a> Sum<&'a Duration> for Duration {
        fn sum<I: Iterator<Item=&'a Duration>>(iter: I) -> Duration {
            iter.fold(Duration::new(0, 0), |a, b| a + *b)
        }
    }

    #[cfg(test)]
    mod tests {
        use super::Duration;

        #[test]
        fn creation() {
            assert!(Duration::from_secs(1) != Duration::from_secs(0));
            assert_eq!(Duration::from_secs(1) + Duration::from_secs(2),
                       Duration::from_secs(3));
            assert_eq!(Duration::from_millis(10) + Duration::from_secs(4),
                       Duration::new(4, 10 * 1_000_000));
            assert_eq!(Duration::from_millis(4000), Duration::new(4, 0));
        }

        #[test]
        fn secs() {
            assert_eq!(Duration::new(0, 0).as_secs(), 0);
            assert_eq!(Duration::from_secs(1).as_secs(), 1);
            assert_eq!(Duration::from_millis(999).as_secs(), 0);
            assert_eq!(Duration::from_millis(1001).as_secs(), 1);
        }

        #[test]
        fn nanos() {
            assert_eq!(Duration::new(0, 0).subsec_nanos(), 0);
            assert_eq!(Duration::new(0, 5).subsec_nanos(), 5);
            assert_eq!(Duration::new(0, 1_000_000_001).subsec_nanos(), 1);
            assert_eq!(Duration::from_secs(1).subsec_nanos(), 0);
            assert_eq!(Duration::from_millis(999).subsec_nanos(), 999 * 1_000_000);
            assert_eq!(Duration::from_millis(1001).subsec_nanos(), 1 * 1_000_000);
        }

        #[test]
        fn add() {
            assert_eq!(Duration::new(0, 0) + Duration::new(0, 1),
                       Duration::new(0, 1));
            assert_eq!(Duration::new(0, 500_000_000) + Duration::new(0, 500_000_001),
                       Duration::new(1, 1));
        }

        #[test]
        fn checked_add() {
            assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)),
                       Some(Duration::new(0, 1)));
            assert_eq!(Duration::new(0, 500_000_000).checked_add(Duration::new(0, 500_000_001)),
                       Some(Duration::new(1, 1)));
            assert_eq!(Duration::new(1, 0).checked_add(Duration::new(::u64::MAX, 0)), None);
        }

        #[test]
        fn sub() {
            assert_eq!(Duration::new(0, 1) - Duration::new(0, 0),
                       Duration::new(0, 1));
            assert_eq!(Duration::new(0, 500_000_001) - Duration::new(0, 500_000_000),
                       Duration::new(0, 1));
            assert_eq!(Duration::new(1, 0) - Duration::new(0, 1),
                       Duration::new(0, 999_999_999));
        }

        #[test]
        fn checked_sub() {
            let zero = Duration::new(0, 0);
            let one_nano = Duration::new(0, 1);
            let one_sec = Duration::new(1, 0);
            assert_eq!(one_nano.checked_sub(zero), Some(Duration::new(0, 1)));
            assert_eq!(one_sec.checked_sub(one_nano),
                       Some(Duration::new(0, 999_999_999)));
            assert_eq!(zero.checked_sub(one_nano), None);
            assert_eq!(zero.checked_sub(one_sec), None);
        }

        #[test] #[should_panic]
        fn sub_bad1() {
            Duration::new(0, 0) - Duration::new(0, 1);
        }

        #[test] #[should_panic]
        fn sub_bad2() {
            Duration::new(0, 0) - Duration::new(1, 0);
        }

        #[test]
        fn mul() {
            assert_eq!(Duration::new(0, 1) * 2, Duration::new(0, 2));
            assert_eq!(Duration::new(1, 1) * 3, Duration::new(3, 3));
            assert_eq!(Duration::new(0, 500_000_001) * 4, Duration::new(2, 4));
            assert_eq!(Duration::new(0, 500_000_001) * 4000,
                       Duration::new(2000, 4000));
        }

        #[test]
        fn checked_mul() {
            assert_eq!(Duration::new(0, 1).checked_mul(2), Some(Duration::new(0, 2)));
            assert_eq!(Duration::new(1, 1).checked_mul(3), Some(Duration::new(3, 3)));
            assert_eq!(Duration::new(0, 500_000_001).checked_mul(4), Some(Duration::new(2, 4)));
            assert_eq!(Duration::new(0, 500_000_001).checked_mul(4000),
                       Some(Duration::new(2000, 4000)));
            assert_eq!(Duration::new(::u64::MAX - 1, 0).checked_mul(2), None);
        }

        #[test]
        fn div() {
            assert_eq!(Duration::new(0, 1) / 2, Duration::new(0, 0));
            assert_eq!(Duration::new(1, 1) / 3, Duration::new(0, 333_333_333));
            assert_eq!(Duration::new(99, 999_999_000) / 100,
                       Duration::new(0, 999_999_990));
        }

        #[test]
        fn checked_div() {
            assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
            assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
            assert_eq!(Duration::new(2, 0).checked_div(0), None);
        }
    }

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