Rollup merge of rust-lang#52813 - newpavlov:duration_mul_div_extras, r=alexcrichton

Duration div mul extras

Successor of rust-lang#52556.

This PR adds the following `impl`s:
- `impl Mul<Duration> for u32` (to allow `10*SECOND` in addition to `SECOND*10`)
- `impl Mul<f64> for Duration` (to allow `2.5*SECOND` vs `2*SECOND + 500*MILLISECOND`)
- `impl Mul<Duration> for f64`
- `impl MulAssign<f64> for Duration`
- `impl Div<f64> for Duration`
- `impl DivAssign<f64> for Duration`
- `impl Div<Duration> for Duration` (`Output = f64`, can be useful e.g. for `duration/MINUTE`)

`f64` is chosen over `f32` to minimize rounding errors. (52 bits fraction precision vs `Duration`'s ~94 bit)

Author: kennytm

src/libcore/time.rs

@@ -21,7 +21,7 @@
 //! assert_eq!(Duration::new(5, 0), Duration::from_secs(5));
 //! ```
 
-use fmt;
+use {fmt, u64};
 use iter::Sum;
 use ops::{Add, Sub, Mul, Div, AddAssign, SubAssign, MulAssign, DivAssign};
 
@@ -30,6 +30,7 @@ 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;
+const MAX_NANOS_F64: f64 = ((u64::MAX as u128 + 1)*(NANOS_PER_SEC as u128)) as f64;
 
 /// A `Duration` type to represent a span of time, typically used for system
 /// timeouts.
@@ -458,6 +459,115 @@ impl Duration {
             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
+    /// ```
+    /// #![feature(duration_float)]
+    /// use std::time::Duration;
+    ///
+    /// let dur = Duration::new(2, 700_000_000);
+    /// assert_eq!(dur.as_float_secs(), 2.7);
+    /// ```
+    #[unstable(feature = "duration_float", issue = "54361")]
+    #[inline]
+    pub fn as_float_secs(&self) -> f64 {
+        (self.secs as f64) + (self.nanos as f64) / (NANOS_PER_SEC as f64)
+    }
+
+    /// Creates a new `Duration` from the specified number of seconds.
+    ///
+    /// # Panics
+    /// This constructor will panic if `secs` is not finite, negative or overflows `Duration`.
+    ///
+    /// # Examples
+    /// ```
+    /// #![feature(duration_float)]
+    /// use std::time::Duration;
+    ///
+    /// let dur = Duration::from_float_secs(2.7);
+    /// assert_eq!(dur, Duration::new(2, 700_000_000));
+    /// ```
+    #[unstable(feature = "duration_float", issue = "54361")]
+    #[inline]
+    pub fn from_float_secs(secs: f64) -> Duration {
+        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,
+        }
+    }
+
+    /// Multiply `Duration` by `f64`.
+    ///
+    /// # Panics
+    /// This method will panic if result is not finite, negative or overflows `Duration`.
+    ///
+    /// # Examples
+    /// ```
+    /// #![feature(duration_float)]
+    /// 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));
+    /// ```
+    #[unstable(feature = "duration_float", issue = "54361")]
+    #[inline]
+    pub fn mul_f64(self, rhs: f64) -> Duration {
+        Duration::from_float_secs(rhs * self.as_float_secs())
+    }
+
+    /// Divide `Duration` by `f64`.
+    ///
+    /// # Panics
+    /// This method will panic if result is not finite, negative or overflows `Duration`.
+    ///
+    /// # Examples
+    /// ```
+    /// #![feature(duration_float)]
+    /// 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));
+    /// ```
+    #[unstable(feature = "duration_float", issue = "54361")]
+    #[inline]
+    pub fn div_f64(self, rhs: f64) -> Duration {
+        Duration::from_float_secs(self.as_float_secs() / rhs)
+    }
+
+    /// Divide `Duration` by `Duration` and return `f64`.
+    ///
+    /// # Examples
+    /// ```
+    /// #![feature(duration_float)]
+    /// 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(dur2), 0.5);
+    /// ```
+    #[unstable(feature = "duration_float", issue = "54361")]
+    #[inline]
+    pub fn div_duration(self, rhs: Duration) -> f64 {
+        self.as_float_secs() / rhs.as_float_secs()
+    }
 }
 
 #[stable(feature = "duration", since = "1.3.0")]
@@ -501,6 +611,15 @@ impl Mul<u32> for Duration {
     }
 }
 
+#[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) {