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    // Copyright 2012-2014 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 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 MILLIS_PER_SEC: u64 = 1_000;

    /// A duration type to represent a span of time, typically used for system
    /// timeouts.
    ///
    /// Each duration is composed of a number of seconds and nanosecond precision.
    /// APIs binding a system timeout will typically round up the nanosecond
    /// precision if the underlying system does not support that level of precision.
    ///
    /// Durations implement many common traits, including `Add`, `Sub`, and other
    /// ops traits. Currently a duration may only be inspected for its number of
    /// seconds and its nanosecond precision.
    ///
    /// # 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)]
    pub struct Duration {
        secs: u64,
        nanos: u32, // Always 0 <= nanos < NANOS_PER_SEC
    }

    impl Duration {
        /// Creates a new `Duration` from the specified number of seconds and
        /// additional nanosecond precision.
        ///
        /// If the 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.
        #[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 seconds.
        #[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.
        #[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 }
        }

        /// Returns the number of whole seconds represented by this duration.
        ///
        /// The extra precision represented by this duration is ignored (e.g. extra
        /// nanoseconds are not represented in the returned value).
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn as_secs(&self) -> u64 { self.secs }

        /// Returns the nanosecond precision represented by this duration.
        ///
        /// 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 (e.g. it is less than one billion).
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        pub fn subsec_nanos(&self) -> u32 { self.nanos }
    }

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

        fn add(self, rhs: Duration) -> Duration {
            let mut secs = self.secs.checked_add(rhs.secs)
                               .expect("overflow when adding durations");
            let mut nanos = self.nanos + rhs.nanos;
            if nanos >= NANOS_PER_SEC {
                nanos -= NANOS_PER_SEC;
                secs = secs.checked_add(1).expect("overflow when adding durations");
            }
            debug_assert!(nanos < NANOS_PER_SEC);
            Duration { secs: secs, nanos: nanos }
        }
    }

    #[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 {
            let mut secs = self.secs.checked_sub(rhs.secs)
                               .expect("overflow when subtracting durations");
            let nanos = if self.nanos >= rhs.nanos {
                self.nanos - rhs.nanos
            } else {
                secs = secs.checked_sub(1)
                           .expect("overflow when subtracting durations");
                self.nanos + NANOS_PER_SEC - rhs.nanos
            };
            debug_assert!(nanos < NANOS_PER_SEC);
            Duration { secs: secs, nanos: nanos }
        }
    }

    #[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 {
            // 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;
            let secs = self.secs.checked_mul(rhs as u64)
                           .and_then(|s| s.checked_add(extra_secs))
                           .expect("overflow when multiplying duration");
            debug_assert!(nanos < NANOS_PER_SEC);
            Duration { secs: secs, nanos: nanos }
        }
    }

    #[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 {
            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);
            Duration { secs: secs, nanos: nanos }
        }
    }

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

    #[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 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] #[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 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));
        }
    }

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