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Rollup merge of rust-lang#102368 - beetrees:nano-niche, r=joshtriplett
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Add a niche to `Duration`, unix `SystemTime`, and non-apple `Instant`

As the nanoseconds fields is always between `0` and `(NANOS_PER_SEC - 1)` inclusive, use the `rustc_layout_scalar_valid_range` attributes to create a niche in the nanosecond field of `Duration` and `Timespec` (which is used to implement unix `SystemTime` and non-apple unix `Instant`; windows `Instant` is implemented with `Duration` and therefore will also benefit). This change has the benefit of making `Option<T>` the same size as `T` for the previously mentioned types. Also shrinks the nanoseconds field of `Timespec` to a `u32` as nanoseconds do not need the extra range of an `i64`, shrinking `Timespec` by 4 bytes on 32-bit platforms.

r? `@joshtriplett`
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@JohnTitor
JohnTitor committed Sep 29, 2022
2 parents 5aff82b + a913277 commit df81a06
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Showing 3 changed files with 75 additions and 61 deletions.
98 changes: 52 additions & 46 deletions library/core/src/time.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,20 @@ const NANOS_PER_MICRO: u32 = 1_000;
const MILLIS_PER_SEC: u64 = 1_000;
const MICROS_PER_SEC: u64 = 1_000_000;

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
#[rustc_layout_scalar_valid_range_start(0)]
#[rustc_layout_scalar_valid_range_end(999_999_999)]
struct Nanoseconds(u32);

impl Default for Nanoseconds {
#[inline]
fn default() -> Self {
// SAFETY: 0 is within the valid range
unsafe { Nanoseconds(0) }
}
}

/// A `Duration` type to represent a span of time, typically used for system
/// timeouts.
///
Expand Down Expand Up @@ -71,7 +85,7 @@ const MICROS_PER_SEC: u64 = 1_000_000;
#[cfg_attr(not(test), rustc_diagnostic_item = "Duration")]
pub struct Duration {
secs: u64,
nanos: u32, // Always 0 <= nanos < NANOS_PER_SEC
nanos: Nanoseconds, // Always 0 <= nanos < NANOS_PER_SEC
}

impl Duration {
Expand Down Expand Up @@ -188,7 +202,8 @@ impl Duration {
None => panic!("overflow in Duration::new"),
};
let nanos = nanos % NANOS_PER_SEC;
Duration { secs, nanos }
// SAFETY: nanos % NANOS_PER_SEC < NANOS_PER_SEC, therefore nanos is within the valid range
Duration { secs, nanos: unsafe { Nanoseconds(nanos) } }
}

/// Creates a new `Duration` from the specified number of whole seconds.
Expand All @@ -208,7 +223,7 @@ impl Duration {
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_secs(secs: u64) -> Duration {
Duration { secs, nanos: 0 }
Duration::new(secs, 0)
}

/// Creates a new `Duration` from the specified number of milliseconds.
Expand All @@ -228,10 +243,7 @@ impl Duration {
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_millis(millis: u64) -> Duration {
Duration {
secs: millis / MILLIS_PER_SEC,
nanos: ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI,
}
Duration::new(millis / MILLIS_PER_SEC, ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI)
}

/// Creates a new `Duration` from the specified number of microseconds.
Expand All @@ -251,10 +263,7 @@ impl Duration {
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_micros(micros: u64) -> Duration {
Duration {
secs: micros / MICROS_PER_SEC,
nanos: ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO,
}
Duration::new(micros / MICROS_PER_SEC, ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO)
}

/// Creates a new `Duration` from the specified number of nanoseconds.
Expand All @@ -274,10 +283,7 @@ impl Duration {
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
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,
}
Duration::new(nanos / (NANOS_PER_SEC as u64), (nanos % (NANOS_PER_SEC as u64)) as u32)
}

/// Returns true if this `Duration` spans no time.
Expand All @@ -301,7 +307,7 @@ impl Duration {
#[rustc_const_stable(feature = "duration_zero", since = "1.53.0")]
#[inline]
pub const fn is_zero(&self) -> bool {
self.secs == 0 && self.nanos == 0
self.secs == 0 && self.nanos.0 == 0
}

/// Returns the number of _whole_ seconds contained by this `Duration`.
Expand Down Expand Up @@ -352,7 +358,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn subsec_millis(&self) -> u32 {
self.nanos / NANOS_PER_MILLI
self.nanos.0 / NANOS_PER_MILLI
}

/// Returns the fractional part of this `Duration`, in whole microseconds.
Expand All @@ -375,7 +381,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn subsec_micros(&self) -> u32 {
self.nanos / NANOS_PER_MICRO
self.nanos.0 / NANOS_PER_MICRO
}

/// Returns the fractional part of this `Duration`, in nanoseconds.
Expand All @@ -398,7 +404,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn subsec_nanos(&self) -> u32 {
self.nanos
self.nanos.0
}

/// Returns the total number of whole milliseconds contained by this `Duration`.
Expand All @@ -416,7 +422,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn as_millis(&self) -> u128 {
self.secs as u128 * MILLIS_PER_SEC as u128 + (self.nanos / NANOS_PER_MILLI) as u128
self.secs as u128 * MILLIS_PER_SEC as u128 + (self.nanos.0 / NANOS_PER_MILLI) as u128
}

/// Returns the total number of whole microseconds contained by this `Duration`.
Expand All @@ -434,7 +440,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn as_micros(&self) -> u128 {
self.secs as u128 * MICROS_PER_SEC as u128 + (self.nanos / NANOS_PER_MICRO) as u128
self.secs as u128 * MICROS_PER_SEC as u128 + (self.nanos.0 / NANOS_PER_MICRO) as u128
}

/// Returns the total number of nanoseconds contained by this `Duration`.
Expand All @@ -452,7 +458,7 @@ impl Duration {
#[must_use]
#[inline]
pub const fn as_nanos(&self) -> u128 {
self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos as u128
self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos.0 as u128
}

/// Checked `Duration` addition. Computes `self + other`, returning [`None`]
Expand All @@ -475,7 +481,7 @@ impl Duration {
#[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
pub const 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;
let mut nanos = self.nanos.0 + rhs.nanos.0;
if nanos >= NANOS_PER_SEC {
nanos -= NANOS_PER_SEC;
if let Some(new_secs) = secs.checked_add(1) {
Expand All @@ -485,7 +491,7 @@ impl Duration {
}
}
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration { secs, nanos })
Some(Duration::new(secs, nanos))
} else {
None
}
Expand Down Expand Up @@ -535,16 +541,16 @@ impl Duration {
#[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
pub const 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
let nanos = if self.nanos.0 >= rhs.nanos.0 {
self.nanos.0 - rhs.nanos.0
} else if let Some(sub_secs) = secs.checked_sub(1) {
secs = sub_secs;
self.nanos + NANOS_PER_SEC - rhs.nanos
self.nanos.0 + NANOS_PER_SEC - rhs.nanos.0
} else {
return None;
};
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration { secs, nanos })
Some(Duration::new(secs, nanos))
} else {
None
}
Expand Down Expand Up @@ -593,13 +599,13 @@ impl Duration {
#[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
pub const 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 total_nanos = self.nanos.0 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(s) = self.secs.checked_mul(rhs as u64) {
if let Some(secs) = s.checked_add(extra_secs) {
debug_assert!(nanos < NANOS_PER_SEC);
return Some(Duration { secs, nanos });
return Some(Duration::new(secs, nanos));
}
}
None
Expand Down Expand Up @@ -653,9 +659,9 @@ impl 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);
let nanos = self.nanos.0 / rhs + (extra_nanos as u32);
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration { secs, nanos })
Some(Duration::new(secs, nanos))
} else {
None
}
Expand All @@ -677,7 +683,7 @@ impl Duration {
#[inline]
#[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
pub const fn as_secs_f64(&self) -> f64 {
(self.secs as f64) + (self.nanos as f64) / (NANOS_PER_SEC as f64)
(self.secs as f64) + (self.nanos.0 as f64) / (NANOS_PER_SEC as f64)
}

/// Returns the number of seconds contained by this `Duration` as `f32`.
Expand All @@ -696,7 +702,7 @@ impl Duration {
#[inline]
#[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
pub const fn as_secs_f32(&self) -> f32 {
(self.secs as f32) + (self.nanos as f32) / (NANOS_PER_SEC as f32)
(self.secs as f32) + (self.nanos.0 as f32) / (NANOS_PER_SEC as f32)
}

/// Creates a new `Duration` from the specified number of seconds represented
Expand Down Expand Up @@ -987,21 +993,21 @@ macro_rules! sum_durations {
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) {
total_nanos = match total_nanos.checked_add(entry.nanos.0 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_nanos % NANOS_PER_SEC as u64) + entry.nanos.0 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 }
Duration::new(total_secs, total_nanos as u32)
}};
}

Expand Down Expand Up @@ -1166,27 +1172,27 @@ impl fmt::Debug for Duration {
let prefix = if f.sign_plus() { "+" } else { "" };

if self.secs > 0 {
fmt_decimal(f, self.secs, self.nanos, NANOS_PER_SEC / 10, prefix, "s")
} else if self.nanos >= NANOS_PER_MILLI {
fmt_decimal(f, self.secs, self.nanos.0, NANOS_PER_SEC / 10, prefix, "s")
} else if self.nanos.0 >= NANOS_PER_MILLI {
fmt_decimal(
f,
(self.nanos / NANOS_PER_MILLI) as u64,
self.nanos % NANOS_PER_MILLI,
(self.nanos.0 / NANOS_PER_MILLI) as u64,
self.nanos.0 % NANOS_PER_MILLI,
NANOS_PER_MILLI / 10,
prefix,
"ms",
)
} else if self.nanos >= NANOS_PER_MICRO {
} else if self.nanos.0 >= NANOS_PER_MICRO {
fmt_decimal(
f,
(self.nanos / NANOS_PER_MICRO) as u64,
self.nanos % NANOS_PER_MICRO,
(self.nanos.0 / NANOS_PER_MICRO) as u64,
self.nanos.0 % NANOS_PER_MICRO,
NANOS_PER_MICRO / 10,
prefix,
"µs",
)
} else {
fmt_decimal(f, self.nanos as u64, 0, 1, prefix, "ns")
fmt_decimal(f, self.nanos.0 as u64, 0, 1, prefix, "ns")
}
}
}
Expand Down Expand Up @@ -1317,7 +1323,7 @@ macro_rules! try_from_secs {
return Err(FromFloatSecsError { kind: FromFloatSecsErrorKind::OverflowOrNan });
};

Ok(Duration { secs, nanos })
Ok(Duration::new(secs, nanos))
}};
}

Expand Down
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