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    #![stable(feature = "duration_core", since = "1.25.0")]

    //! Temporal quantification.
    //!
    //! Example:
    //!
    //! ```
    //! use std::time::Duration;
    //!
    //! let five_seconds = Duration::new(5, 0);
    //! // both declarations are equivalent
    //! assert_eq!(Duration::new(5, 0), Duration::from_secs(5));
    //! ```

    use crate::iter::Sum;
    use crate::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
    use crate::{fmt, u64};

    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, Hash, Default)]
    pub struct Duration {
        secs: u64,
        nanos: u32, // Always 0 <= nanos < NANOS_PER_SEC
    }

    impl Duration {
        /// The duration of one second.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(duration_constants)]
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::SECOND, Duration::from_secs(1));
        /// ```
        #[unstable(feature = "duration_constants", issue = "57391")]
        pub const SECOND: Duration = Duration::from_secs(1);

        /// The duration of one millisecond.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(duration_constants)]
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::MILLISECOND, Duration::from_millis(1));
        /// ```
        #[unstable(feature = "duration_constants", issue = "57391")]
        pub const MILLISECOND: Duration = Duration::from_millis(1);

        /// The duration of one microsecond.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(duration_constants)]
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::MICROSECOND, Duration::from_micros(1));
        /// ```
        #[unstable(feature = "duration_constants", issue = "57391")]
        pub const MICROSECOND: Duration = Duration::from_micros(1);

        /// The duration of one nanosecond.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(duration_constants)]
        /// use std::time::Duration;
        ///
        /// assert_eq!(Duration::NANOSECOND, Duration::from_nanos(1));
        /// ```
        #[unstable(feature = "duration_constants", issue = "57391")]
        pub const NANOSECOND: Duration = Duration::from_nanos(1);

        /// 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, 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]
        #[rustc_promotable]
        pub const fn from_secs(secs: u64) -> Duration {
            Duration { 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!(569_000_000, duration.subsec_nanos());
        /// ```
        #[stable(feature = "duration", since = "1.3.0")]
        #[inline]
        #[rustc_promotable]
        pub const fn from_millis(millis: u64) -> Duration {
            Duration {
                secs: millis / MILLIS_PER_SEC,
                nanos: ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI,
            }
        }

        /// Creates a new `Duration` from the specified number of microseconds.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_micros(1_000_002);
        ///
        /// assert_eq!(1, duration.as_secs());
        /// assert_eq!(2000, duration.subsec_nanos());
        /// ```
        #[stable(feature = "duration_from_micros", since = "1.27.0")]
        #[inline]
        #[rustc_promotable]
        pub const fn from_micros(micros: u64) -> Duration {
            Duration {
                secs: micros / MICROS_PER_SEC,
                nanos: ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO,
            }
        }

        /// Creates a new `Duration` from the specified number of nanoseconds.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_nanos(1_000_000_123);
        ///
        /// assert_eq!(1, duration.as_secs());
        /// assert_eq!(123, duration.subsec_nanos());
        /// ```
        #[stable(feature = "duration_extras", since = "1.27.0")]
        #[inline]
        #[rustc_promotable]
        pub const fn from_nanos(nanos: u64) -> Duration {
            Duration {
                secs: nanos / (NANOS_PER_SEC as u64),
                nanos: (nanos % (NANOS_PER_SEC as u64)) as u32,
            }
        }

        /// 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 const fn as_secs(&self) -> u64 {
            self.secs
        }

        /// Returns the fractional part of this `Duration`, in whole milliseconds.
        ///
        /// This method does **not** return the length of the duration when
        /// represented by milliseconds. The returned number always represents a
        /// fractional portion of a second (i.e., it is less than one thousand).
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_millis(5432);
        /// assert_eq!(duration.as_secs(), 5);
        /// assert_eq!(duration.subsec_millis(), 432);
        /// ```
        #[stable(feature = "duration_extras", since = "1.27.0")]
        #[inline]
        pub const fn subsec_millis(&self) -> u32 {
            self.nanos / NANOS_PER_MILLI
        }

        /// Returns the fractional part of this `Duration`, in whole microseconds.
        ///
        /// This method does **not** return the length of the duration when
        /// represented by microseconds. The returned number always represents a
        /// fractional portion of a second (i.e., it is less than one million).
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::from_micros(1_234_567);
        /// assert_eq!(duration.as_secs(), 1);
        /// assert_eq!(duration.subsec_micros(), 234_567);
        /// ```
        #[stable(feature = "duration_extras", since = "1.27.0")]
        #[inline]
        pub const fn subsec_micros(&self) -> u32 {
            self.nanos / NANOS_PER_MICRO
        }

        /// 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 const fn subsec_nanos(&self) -> u32 {
            self.nanos
        }

        /// Returns the total number of whole milliseconds contained by this `Duration`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::new(5, 730023852);
        /// assert_eq!(duration.as_millis(), 5730);
        /// ```
        #[stable(feature = "duration_as_u128", since = "1.33.0")]
        #[inline]
        pub const fn as_millis(&self) -> u128 {
            self.secs as u128 * MILLIS_PER_SEC as u128 + (self.nanos / NANOS_PER_MILLI) as u128
        }

        /// Returns the total number of whole microseconds contained by this `Duration`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::new(5, 730023852);
        /// assert_eq!(duration.as_micros(), 5730023);
        /// ```
        #[stable(feature = "duration_as_u128", since = "1.33.0")]
        #[inline]
        pub const fn as_micros(&self) -> u128 {
            self.secs as u128 * MICROS_PER_SEC as u128 + (self.nanos / NANOS_PER_MICRO) as u128
        }

        /// Returns the total number of nanoseconds contained by this `Duration`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::time::Duration;
        ///
        /// let duration = Duration::new(5, 730023852);
        /// assert_eq!(duration.as_nanos(), 5730023852);
        /// ```
        #[stable(feature = "duration_as_u128", since = "1.33.0")]
        #[inline]
        pub const fn as_nanos(&self) -> u128 {
            self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos as u128
        }

        /// 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 overflow 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, 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, nanos })
            } else {
                None
            }
        }

        /// Returns the number of seconds contained by this `Duration` as `f64`.
        ///
        /// The returned value does include the fractional (nanosecond) part of the duration.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// assert_eq!(dur.as_secs_f64(), 2.7);
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn as_secs_f64(&self) -> f64 {
            (self.secs as f64) + (self.nanos as f64) / (NANOS_PER_SEC as f64)
        }

        /// Returns the number of seconds contained by this `Duration` as `f32`.
        ///
        /// The returned value does include the fractional (nanosecond) part of the duration.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// assert_eq!(dur.as_secs_f32(), 2.7);
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn as_secs_f32(&self) -> f32 {
            (self.secs as f32) + (self.nanos as f32) / (NANOS_PER_SEC as f32)
        }

        /// Creates a new `Duration` from the specified number of seconds represented
        /// as `f64`.
        ///
        /// # Panics
        /// This constructor will panic if `secs` is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::from_secs_f64(2.7);
        /// assert_eq!(dur, Duration::new(2, 700_000_000));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn from_secs_f64(secs: f64) -> Duration {
            const MAX_NANOS_F64: f64 = ((u64::MAX as u128 + 1) * (NANOS_PER_SEC as u128)) as f64;
            let nanos = secs * (NANOS_PER_SEC as f64);
            if !nanos.is_finite() {
                panic!("got non-finite value when converting float to duration");
            }
            if nanos >= MAX_NANOS_F64 {
                panic!("overflow when converting float to duration");
            }
            if nanos < 0.0 {
                panic!("underflow when converting float to duration");
            }
            let nanos = nanos as u128;
            Duration {
                secs: (nanos / (NANOS_PER_SEC as u128)) as u64,
                nanos: (nanos % (NANOS_PER_SEC as u128)) as u32,
            }
        }

        /// Creates a new `Duration` from the specified number of seconds represented
        /// as `f32`.
        ///
        /// # Panics
        /// This constructor will panic if `secs` is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::from_secs_f32(2.7);
        /// assert_eq!(dur, Duration::new(2, 700_000_000));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn from_secs_f32(secs: f32) -> Duration {
            const MAX_NANOS_F32: f32 = ((u64::MAX as u128 + 1) * (NANOS_PER_SEC as u128)) as f32;
            let nanos = secs * (NANOS_PER_SEC as f32);
            if !nanos.is_finite() {
                panic!("got non-finite value when converting float to duration");
            }
            if nanos >= MAX_NANOS_F32 {
                panic!("overflow when converting float to duration");
            }
            if nanos < 0.0 {
                panic!("underflow when converting float to duration");
            }
            let nanos = nanos as u128;
            Duration {
                secs: (nanos / (NANOS_PER_SEC as u128)) as u64,
                nanos: (nanos % (NANOS_PER_SEC as u128)) as u32,
            }
        }

        /// Multiplies `Duration` by `f64`.
        ///
        /// # Panics
        /// This method will panic if result is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// assert_eq!(dur.mul_f64(3.14), Duration::new(8, 478_000_000));
        /// assert_eq!(dur.mul_f64(3.14e5), Duration::new(847_800, 0));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn mul_f64(self, rhs: f64) -> Duration {
            Duration::from_secs_f64(rhs * self.as_secs_f64())
        }

        /// Multiplies `Duration` by `f32`.
        ///
        /// # Panics
        /// This method will panic if result is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// // note that due to rounding errors result is slightly different
        /// // from 8.478 and 847800.0
        /// assert_eq!(dur.mul_f32(3.14), Duration::new(8, 478_000_640));
        /// assert_eq!(dur.mul_f32(3.14e5), Duration::new(847799, 969_120_256));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn mul_f32(self, rhs: f32) -> Duration {
            Duration::from_secs_f32(rhs * self.as_secs_f32())
        }

        /// Divide `Duration` by `f64`.
        ///
        /// # Panics
        /// This method will panic if result is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// assert_eq!(dur.div_f64(3.14), Duration::new(0, 859_872_611));
        /// // note that truncation is used, not rounding
        /// assert_eq!(dur.div_f64(3.14e5), Duration::new(0, 8_598));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn div_f64(self, rhs: f64) -> Duration {
            Duration::from_secs_f64(self.as_secs_f64() / rhs)
        }

        /// Divide `Duration` by `f32`.
        ///
        /// # Panics
        /// This method will panic if result is not finite, negative or overflows `Duration`.
        ///
        /// # Examples
        /// ```
        /// use std::time::Duration;
        ///
        /// let dur = Duration::new(2, 700_000_000);
        /// // note that due to rounding errors result is slightly
        /// // different from 0.859_872_611
        /// assert_eq!(dur.div_f32(3.14), Duration::new(0, 859_872_576));
        /// // note that truncation is used, not rounding
        /// assert_eq!(dur.div_f32(3.14e5), Duration::new(0, 8_598));
        /// ```
        #[stable(feature = "duration_float", since = "1.38.0")]
        #[inline]
        pub fn div_f32(self, rhs: f32) -> Duration {
            Duration::from_secs_f32(self.as_secs_f32() / rhs)
        }

        /// Divide `Duration` by `Duration` and return `f64`.
        ///
        /// # Examples
        /// ```
        /// #![feature(div_duration)]
        /// use std::time::Duration;
        ///
        /// let dur1 = Duration::new(2, 700_000_000);
        /// let dur2 = Duration::new(5, 400_000_000);
        /// assert_eq!(dur1.div_duration_f64(dur2), 0.5);
        /// ```
        #[unstable(feature = "div_duration", issue = "63139")]
        #[inline]
        pub fn div_duration_f64(self, rhs: Duration) -> f64 {
            self.as_secs_f64() / rhs.as_secs_f64()
        }

        /// Divide `Duration` by `Duration` and return `f32`.
        ///
        /// # Examples
        /// ```
        /// #![feature(div_duration)]
        /// use std::time::Duration;
        ///
        /// let dur1 = Duration::new(2, 700_000_000);
        /// let dur2 = Duration::new(5, 400_000_000);
        /// assert_eq!(dur1.div_duration_f32(dur2), 0.5);
        /// ```
        #[unstable(feature = "div_duration", issue = "63139")]
        #[inline]
        pub fn div_duration_f32(self, rhs: Duration) -> f32 {
            self.as_secs_f32() / rhs.as_secs_f32()
        }
    }

    #[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 = "symmetric_u32_duration_mul", since = "1.31.0")]
    impl Mul<Duration> for u32 {
        type Output = Duration;

        fn mul(self, rhs: Duration) -> Duration {
            rhs * self
        }
    }

    #[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;
        }
    }

    macro_rules! sum_durations {
        ($iter:expr) => {{
            let mut total_secs: u64 = 0;
            let mut total_nanos: u64 = 0;

            for entry in $iter {
                total_secs =
                    total_secs.checked_add(entry.secs).expect("overflow in iter::sum over durations");
                total_nanos = match total_nanos.checked_add(entry.nanos as u64) {
                    Some(n) => n,
                    None => {
                        total_secs = total_secs
                            .checked_add(total_nanos / NANOS_PER_SEC as u64)
                            .expect("overflow in iter::sum over durations");
                        (total_nanos % NANOS_PER_SEC as u64) + entry.nanos as u64
                    }
                };
            }
            total_secs = total_secs
                .checked_add(total_nanos / NANOS_PER_SEC as u64)
                .expect("overflow in iter::sum over durations");
            total_nanos = total_nanos % NANOS_PER_SEC as u64;
            Duration { secs: total_secs, nanos: total_nanos as u32 }
        }};
    }

    #[stable(feature = "duration_sum", since = "1.16.0")]
    impl Sum for Duration {
        fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
            sum_durations!(iter)
        }
    }

    #[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 {
            sum_durations!(iter)
        }
    }

    #[stable(feature = "duration_debug_impl", since = "1.27.0")]
    impl fmt::Debug for Duration {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            /// Formats a floating point number in decimal notation.
            ///
            /// The number is given as the `integer_part` and a fractional part.
            /// The value of the fractional part is `fractional_part / divisor`. So
            /// `integer_part` = 3, `fractional_part` = 12 and `divisor` = 100
            /// represents the number `3.012`. Trailing zeros are omitted.
            ///
            /// `divisor` must not be above 100_000_000. It also should be a power
            /// of 10, everything else doesn't make sense. `fractional_part` has
            /// to be less than `10 * divisor`!
            fn fmt_decimal(
                f: &mut fmt::Formatter<'_>,
                mut integer_part: u64,
                mut fractional_part: u32,
                mut divisor: u32,
            ) -> fmt::Result {
                // Encode the fractional part into a temporary buffer. The buffer
                // only need to hold 9 elements, because `fractional_part` has to
                // be smaller than 10^9. The buffer is prefilled with '0' digits
                // to simplify the code below.
                let mut buf = [b'0'; 9];

                // The next digit is written at this position
                let mut pos = 0;

                // We keep writing digits into the buffer while there are non-zero
                // digits left and we haven't written enough digits yet.
                while fractional_part > 0 && pos < f.precision().unwrap_or(9) {
                    // Write new digit into the buffer
                    buf[pos] = b'0' + (fractional_part / divisor) as u8;

                    fractional_part %= divisor;
                    divisor /= 10;
                    pos += 1;
                }

                // If a precision < 9 was specified, there may be some non-zero
                // digits left that weren't written into the buffer. In that case we
                // need to perform rounding to match the semantics of printing
                // normal floating point numbers. However, we only need to do work
                // when rounding up. This happens if the first digit of the
                // remaining ones is >= 5.
                if fractional_part > 0 && fractional_part >= divisor * 5 {
                    // Round up the number contained in the buffer. We go through
                    // the buffer backwards and keep track of the carry.
                    let mut rev_pos = pos;
                    let mut carry = true;
                    while carry && rev_pos > 0 {
                        rev_pos -= 1;

                        // If the digit in the buffer is not '9', we just need to
                        // increment it and can stop then (since we don't have a
                        // carry anymore). Otherwise, we set it to '0' (overflow)
                        // and continue.
                        if buf[rev_pos] < b'9' {
                            buf[rev_pos] += 1;
                            carry = false;
                        } else {
                            buf[rev_pos] = b'0';
                        }
                    }

                    // If we still have the carry bit set, that means that we set
                    // the whole buffer to '0's and need to increment the integer
                    // part.
                    if carry {
                        integer_part += 1;
                    }
                }

                // Determine the end of the buffer: if precision is set, we just
                // use as many digits from the buffer (capped to 9). If it isn't
                // set, we only use all digits up to the last non-zero one.
                let end = f.precision().map(|p| crate::cmp::min(p, 9)).unwrap_or(pos);

                // If we haven't emitted a single fractional digit and the precision
                // wasn't set to a non-zero value, we don't print the decimal point.
                if end == 0 {
                    write!(f, "{}", integer_part)
                } else {
                    // SAFETY: We are only writing ASCII digits into the buffer and it was
                    // initialized with '0's, so it contains valid UTF8.
                    let s = unsafe { crate::str::from_utf8_unchecked(&buf[..end]) };

                    // If the user request a precision > 9, we pad '0's at the end.
                    let w = f.precision().unwrap_or(pos);
                    write!(f, "{}.{:0<width$}", integer_part, s, width = w)
                }
            }

            // Print leading '+' sign if requested
            if f.sign_plus() {
                write!(f, "+")?;
            }

            if self.secs > 0 {
                fmt_decimal(f, self.secs, self.nanos, 100_000_000)?;
                f.write_str("s")
            } else if self.nanos >= 1_000_000 {
                fmt_decimal(f, self.nanos as u64 / 1_000_000, self.nanos % 1_000_000, 100_000)?;
                f.write_str("ms")
            } else if self.nanos >= 1_000 {
                fmt_decimal(f, self.nanos as u64 / 1_000, self.nanos % 1_000, 100)?;
                f.write_str("µs")
            } else {
                fmt_decimal(f, self.nanos as u64, 0, 1)?;
                f.write_str("ns")
            }
        }
    }