library/std/src/sys/unix/time.rs - toolchain/rustc - Git at Google

 use crate::fmt;
 use crate::time::Duration;

 pub use self::inner::Instant;

 const NSEC_PER_SEC: u64 = 1_000_000_000;
 pub const UNIX_EPOCH: SystemTime = SystemTime { t: Timespec::zero() };
 #[allow(dead_code)] // Used for pthread condvar timeouts
 pub const TIMESPEC_MAX: libc::timespec =
     libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };

 // This additional constant is only used when calling
 // `libc::pthread_cond_timedwait`.
 #[cfg(target_os = "nto")]
 pub(super) const TIMESPEC_MAX_CAPPED: libc::timespec = libc::timespec {
     tv_sec: (u64::MAX / NSEC_PER_SEC) as i64,
     tv_nsec: (u64::MAX % NSEC_PER_SEC) as i64,
 };

 #[derive(Copy, Clone, 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);

 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SystemTime {
     pub(in crate::sys::unix) t: Timespec,
 }

 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub(in crate::sys::unix) struct Timespec {
     tv_sec: i64,
     tv_nsec: Nanoseconds,
 }

 impl SystemTime {
     #[cfg_attr(target_os = "horizon", allow(unused))]
     pub fn new(tv_sec: i64, tv_nsec: i64) -> SystemTime {
         SystemTime { t: Timespec::new(tv_sec, tv_nsec) }
     }

     pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
         self.t.sub_timespec(&other.t)
     }

     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
         Some(SystemTime { t: self.t.checked_add_duration(other)? })
     }

     pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
         Some(SystemTime { t: self.t.checked_sub_duration(other)? })
     }
 }

 impl From<libc::timespec> for SystemTime {
     fn from(t: libc::timespec) -> SystemTime {
         SystemTime { t: Timespec::from(t) }
     }
 }

 impl fmt::Debug for SystemTime {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("SystemTime")
             .field("tv_sec", &self.t.tv_sec)
             .field("tv_nsec", &self.t.tv_nsec.0)
             .finish()
     }
 }

 impl Timespec {
     pub const fn zero() -> Timespec {
         Timespec::new(0, 0)
     }

     const fn new(tv_sec: i64, tv_nsec: i64) -> Timespec {
         assert!(tv_nsec >= 0 && tv_nsec < NSEC_PER_SEC as i64);
         // SAFETY: The assert above checks tv_nsec is within the valid range
         Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds(tv_nsec as u32) } }
     }

     pub fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
         if self >= other {
             // NOTE(eddyb) two aspects of this `if`-`else` are required for LLVM
             // to optimize it into a branchless form (see also #75545):
             //
             // 1. `self.tv_sec - other.tv_sec` shows up as a common expression
             //    in both branches, i.e. the `else` must have its `- 1`
             //    subtraction after the common one, not interleaved with it
             //    (it used to be `self.tv_sec - 1 - other.tv_sec`)
             //
             // 2. the `Duration::new` call (or any other additional complexity)
             //    is outside of the `if`-`else`, not duplicated in both branches
             //
             // Ideally this code could be rearranged such that it more
             // directly expresses the lower-cost behavior we want from it.
             let (secs, nsec) = if self.tv_nsec.0 >= other.tv_nsec.0 {
                 ((self.tv_sec - other.tv_sec) as u64, self.tv_nsec.0 - other.tv_nsec.0)
             } else {
                 (
                     (self.tv_sec - other.tv_sec - 1) as u64,
                     self.tv_nsec.0 + (NSEC_PER_SEC as u32) - other.tv_nsec.0,
                 )
             };

             Ok(Duration::new(secs, nsec))
         } else {
             match other.sub_timespec(self) {
                 Ok(d) => Err(d),
                 Err(d) => Ok(d),
             }
         }
     }

     pub fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = self.tv_sec.checked_add_unsigned(other.as_secs())?;

         // Nano calculations can't overflow because nanos are <1B which fit
         // in a u32.
         let mut nsec = other.subsec_nanos() + self.tv_nsec.0;
         if nsec >= NSEC_PER_SEC as u32 {
             nsec -= NSEC_PER_SEC as u32;
             secs = secs.checked_add(1)?;
         }
         Some(Timespec::new(secs, nsec.into()))
     }

     pub fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = self.tv_sec.checked_sub_unsigned(other.as_secs())?;

         // Similar to above, nanos can't overflow.
         let mut nsec = self.tv_nsec.0 as i32 - other.subsec_nanos() as i32;
         if nsec < 0 {
             nsec += NSEC_PER_SEC as i32;
             secs = secs.checked_sub(1)?;
         }
         Some(Timespec::new(secs, nsec.into()))
     }

     #[allow(dead_code)]
     pub fn to_timespec(&self) -> Option<libc::timespec> {
         Some(libc::timespec {
             tv_sec: self.tv_sec.try_into().ok()?,
             tv_nsec: self.tv_nsec.0.try_into().ok()?,
         })
     }

     // On QNX Neutrino, the maximum timespec for e.g. pthread_cond_timedwait
     // is 2^64 nanoseconds
     #[cfg(target_os = "nto")]
     pub(super) fn to_timespec_capped(&self) -> Option<libc::timespec> {
         // Check if timeout in nanoseconds would fit into an u64
         if (self.tv_nsec.0 as u64)
             .checked_add((self.tv_sec as u64).checked_mul(NSEC_PER_SEC)?)
             .is_none()
         {
             return None;
         }
         self.to_timespec()
     }

     #[cfg(all(
         target_os = "linux",
         target_env = "gnu",
         target_pointer_width = "32",
         not(target_arch = "riscv32")
     ))]
     pub fn to_timespec64(&self) -> __timespec64 {
         __timespec64::new(self.tv_sec, self.tv_nsec.0 as _)
     }
 }

 impl From<libc::timespec> for Timespec {
     fn from(t: libc::timespec) -> Timespec {
         Timespec::new(t.tv_sec as i64, t.tv_nsec as i64)
     }
 }

 #[cfg(all(
     target_os = "linux",
     target_env = "gnu",
     target_pointer_width = "32",
     not(target_arch = "riscv32")
 ))]
 #[repr(C)]
 pub(in crate::sys::unix) struct __timespec64 {
     pub(in crate::sys::unix) tv_sec: i64,
     #[cfg(target_endian = "big")]
     _padding: i32,
     pub(in crate::sys::unix) tv_nsec: i32,
     #[cfg(target_endian = "little")]
     _padding: i32,
 }

 #[cfg(all(
     target_os = "linux",
     target_env = "gnu",
     target_pointer_width = "32",
     not(target_arch = "riscv32")
 ))]
 impl __timespec64 {
     pub(in crate::sys::unix) fn new(tv_sec: i64, tv_nsec: i32) -> Self {
         Self { tv_sec, tv_nsec, _padding: 0 }
     }
 }

 #[cfg(all(
     target_os = "linux",
     target_env = "gnu",
     target_pointer_width = "32",
     not(target_arch = "riscv32")
 ))]
 impl From<__timespec64> for Timespec {
     fn from(t: __timespec64) -> Timespec {
         Timespec::new(t.tv_sec, t.tv_nsec.into())
     }
 }

 #[cfg(any(
     all(target_os = "macos", any(not(target_arch = "aarch64"))),
     target_os = "ios",
     target_os = "watchos"
 ))]
 mod inner {
     use crate::sync::atomic::{AtomicU64, Ordering};
     use crate::sys::cvt;
     use crate::sys_common::mul_div_u64;
     use crate::time::Duration;

     use super::{SystemTime, Timespec, NSEC_PER_SEC};

     #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
     pub struct Instant {
         t: u64,
     }

     #[repr(C)]
     #[derive(Copy, Clone)]
     struct mach_timebase_info {
         numer: u32,
         denom: u32,
     }
     type mach_timebase_info_t = *mut mach_timebase_info;
     type kern_return_t = libc::c_int;

     impl Instant {
         pub fn now() -> Instant {
             extern "C" {
                 fn mach_absolute_time() -> u64;
             }
             Instant { t: unsafe { mach_absolute_time() } }
         }

         pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
             let diff = self.t.checked_sub(other.t)?;
             let info = info();
             let nanos = mul_div_u64(diff, info.numer as u64, info.denom as u64);
             Some(Duration::new(nanos / NSEC_PER_SEC, (nanos % NSEC_PER_SEC) as u32))
         }

         pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
             Some(Instant { t: self.t.checked_add(checked_dur2intervals(other)?)? })
         }

         pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
             Some(Instant { t: self.t.checked_sub(checked_dur2intervals(other)?)? })
         }
     }

     impl SystemTime {
         pub fn now() -> SystemTime {
             use crate::ptr;

             let mut s = libc::timeval { tv_sec: 0, tv_usec: 0 };
             cvt(unsafe { libc::gettimeofday(&mut s, ptr::null_mut()) }).unwrap();
             return SystemTime::from(s);
         }
     }

     impl From<libc::timeval> for Timespec {
         fn from(t: libc::timeval) -> Timespec {
             Timespec::new(t.tv_sec as i64, 1000 * t.tv_usec as i64)
         }
     }

     impl From<libc::timeval> for SystemTime {
         fn from(t: libc::timeval) -> SystemTime {
             SystemTime { t: Timespec::from(t) }
         }
     }

     fn checked_dur2intervals(dur: &Duration) -> Option<u64> {
         let nanos =
             dur.as_secs().checked_mul(NSEC_PER_SEC)?.checked_add(dur.subsec_nanos() as u64)?;
         let info = info();
         Some(mul_div_u64(nanos, info.denom as u64, info.numer as u64))
     }

     fn info() -> mach_timebase_info {
         // INFO_BITS conceptually is an `Option<mach_timebase_info>`. We can do
         // this in 64 bits because we know 0 is never a valid value for the
         // `denom` field.
         //
         // Encoding this as a single `AtomicU64` allows us to use `Relaxed`
         // operations, as we are only interested in the effects on a single
         // memory location.
         static INFO_BITS: AtomicU64 = AtomicU64::new(0);

         // If a previous thread has initialized `INFO_BITS`, use it.
         let info_bits = INFO_BITS.load(Ordering::Relaxed);
         if info_bits != 0 {
             return info_from_bits(info_bits);
         }

         // ... otherwise learn for ourselves ...
         extern "C" {
             fn mach_timebase_info(info: mach_timebase_info_t) -> kern_return_t;
         }

         let mut info = info_from_bits(0);
         unsafe {
             mach_timebase_info(&mut info);
         }
         INFO_BITS.store(info_to_bits(info), Ordering::Relaxed);
         info
     }

     #[inline]
     fn info_to_bits(info: mach_timebase_info) -> u64 {
         ((info.denom as u64) << 32) | (info.numer as u64)
     }

     #[inline]
     fn info_from_bits(bits: u64) -> mach_timebase_info {
         mach_timebase_info { numer: bits as u32, denom: (bits >> 32) as u32 }
     }
 }

 #[cfg(not(any(
     all(target_os = "macos", any(not(target_arch = "aarch64"))),
     target_os = "ios",
     target_os = "watchos"
 )))]
 mod inner {
     use crate::fmt;
     use crate::mem::MaybeUninit;
     use crate::sys::cvt;
     use crate::time::Duration;

     use super::{SystemTime, Timespec};

     #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
     pub struct Instant {
         t: Timespec,
     }

     impl Instant {
         pub fn now() -> Instant {
             #[cfg(target_os = "macos")]
             const clock_id: libc::clockid_t = libc::CLOCK_UPTIME_RAW;
             #[cfg(not(target_os = "macos"))]
             const clock_id: libc::clockid_t = libc::CLOCK_MONOTONIC;
             Instant { t: Timespec::now(clock_id) }
         }

         pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
             self.t.sub_timespec(&other.t).ok()
         }

         pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
             Some(Instant { t: self.t.checked_add_duration(other)? })
         }

         pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
             Some(Instant { t: self.t.checked_sub_duration(other)? })
         }
     }

     impl fmt::Debug for Instant {
         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             f.debug_struct("Instant")
                 .field("tv_sec", &self.t.tv_sec)
                 .field("tv_nsec", &self.t.tv_nsec.0)
                 .finish()
         }
     }

     impl SystemTime {
         pub fn now() -> SystemTime {
             SystemTime { t: Timespec::now(libc::CLOCK_REALTIME) }
         }
     }

     impl Timespec {
         pub fn now(clock: libc::clockid_t) -> Timespec {
             // Try to use 64-bit time in preparation for Y2038.
             #[cfg(all(
                 target_os = "linux",
                 target_env = "gnu",
                 target_pointer_width = "32",
                 not(target_arch = "riscv32")
             ))]
             {
                 use crate::sys::weak::weak;

                 // __clock_gettime64 was added to 32-bit arches in glibc 2.34,
                 // and it handles both vDSO calls and ENOSYS fallbacks itself.
                 weak!(fn __clock_gettime64(libc::clockid_t, *mut super::__timespec64) -> libc::c_int);

                 if let Some(clock_gettime64) = __clock_gettime64.get() {
                     let mut t = MaybeUninit::uninit();
                     cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
                     return Timespec::from(unsafe { t.assume_init() });
                 }
             }

             let mut t = MaybeUninit::uninit();
             cvt(unsafe { libc::clock_gettime(clock, t.as_mut_ptr()) }).unwrap();
             Timespec::from(unsafe { t.assume_init() })
         }
     }
 }
	use crate::fmt;
	use crate::time::Duration;

	pub use self::inner::Instant;

	const NSEC_PER_SEC: u64 = 1_000_000_000;
	pub const UNIX_EPOCH: SystemTime = SystemTime { t: Timespec::zero() };
	#[allow(dead_code)] // Used for pthread condvar timeouts
	pub const TIMESPEC_MAX: libc::timespec =
	libc::timespec { tv_sec: <libc::time_t>::MAX, tv_nsec: 1_000_000_000 - 1 };

	// This additional constant is only used when calling
	// `libc::pthread_cond_timedwait`.
	#[cfg(target_os = "nto")]
	pub(super) const TIMESPEC_MAX_CAPPED: libc::timespec = libc::timespec {
	tv_sec: (u64::MAX / NSEC_PER_SEC) as i64,
	tv_nsec: (u64::MAX % NSEC_PER_SEC) as i64,
	};

	#[derive(Copy, Clone, 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);

	#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
	pub struct SystemTime {
	pub(in crate::sys::unix) t: Timespec,
	}

	#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
	pub(in crate::sys::unix) struct Timespec {
	tv_sec: i64,
	tv_nsec: Nanoseconds,
	}

	impl SystemTime {
	#[cfg_attr(target_os = "horizon", allow(unused))]
	pub fn new(tv_sec: i64, tv_nsec: i64) -> SystemTime {
	SystemTime { t: Timespec::new(tv_sec, tv_nsec) }
	}

	pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
	self.t.sub_timespec(&other.t)
	}

	pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
	Some(SystemTime { t: self.t.checked_add_duration(other)? })
	}

	pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
	Some(SystemTime { t: self.t.checked_sub_duration(other)? })
	}
	}

	impl From<libc::timespec> for SystemTime {
	fn from(t: libc::timespec) -> SystemTime {
	SystemTime { t: Timespec::from(t) }
	}
	}

	impl fmt::Debug for SystemTime {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	f.debug_struct("SystemTime")
	.field("tv_sec", &self.t.tv_sec)
	.field("tv_nsec", &self.t.tv_nsec.0)
	.finish()
	}
	}

	impl Timespec {
	pub const fn zero() -> Timespec {
	Timespec::new(0, 0)
	}

	const fn new(tv_sec: i64, tv_nsec: i64) -> Timespec {
	assert!(tv_nsec >= 0 && tv_nsec < NSEC_PER_SEC as i64);
	// SAFETY: The assert above checks tv_nsec is within the valid range
	Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds(tv_nsec as u32) } }
	}

	pub fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
	if self >= other {
	// NOTE(eddyb) two aspects of this `if`-`else` are required for LLVM
	// to optimize it into a branchless form (see also #75545):
	//
	// 1. `self.tv_sec - other.tv_sec` shows up as a common expression
	// in both branches, i.e. the `else` must have its `- 1`
	// subtraction after the common one, not interleaved with it
	// (it used to be `self.tv_sec - 1 - other.tv_sec`)
	//
	// 2. the `Duration::new` call (or any other additional complexity)
	// is outside of the `if`-`else`, not duplicated in both branches
	//
	// Ideally this code could be rearranged such that it more
	// directly expresses the lower-cost behavior we want from it.
	let (secs, nsec) = if self.tv_nsec.0 >= other.tv_nsec.0 {
	((self.tv_sec - other.tv_sec) as u64, self.tv_nsec.0 - other.tv_nsec.0)
	} else {
	(
	(self.tv_sec - other.tv_sec - 1) as u64,
	self.tv_nsec.0 + (NSEC_PER_SEC as u32) - other.tv_nsec.0,
	)
	};

	Ok(Duration::new(secs, nsec))
	} else {
	match other.sub_timespec(self) {
	Ok(d) => Err(d),
	Err(d) => Ok(d),
	}
	}
	}

	pub fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
	let mut secs = self.tv_sec.checked_add_unsigned(other.as_secs())?;

	// Nano calculations can't overflow because nanos are <1B which fit
	// in a u32.
	let mut nsec = other.subsec_nanos() + self.tv_nsec.0;
	if nsec >= NSEC_PER_SEC as u32 {
	nsec -= NSEC_PER_SEC as u32;
	secs = secs.checked_add(1)?;
	}
	Some(Timespec::new(secs, nsec.into()))
	}

	pub fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
	let mut secs = self.tv_sec.checked_sub_unsigned(other.as_secs())?;

	// Similar to above, nanos can't overflow.
	let mut nsec = self.tv_nsec.0 as i32 - other.subsec_nanos() as i32;
	if nsec < 0 {
	nsec += NSEC_PER_SEC as i32;
	secs = secs.checked_sub(1)?;
	}
	Some(Timespec::new(secs, nsec.into()))
	}

	#[allow(dead_code)]
	pub fn to_timespec(&self) -> Option<libc::timespec> {
	Some(libc::timespec {
	tv_sec: self.tv_sec.try_into().ok()?,
	tv_nsec: self.tv_nsec.0.try_into().ok()?,
	})
	}

	// On QNX Neutrino, the maximum timespec for e.g. pthread_cond_timedwait
	// is 2^64 nanoseconds
	#[cfg(target_os = "nto")]
	pub(super) fn to_timespec_capped(&self) -> Option<libc::timespec> {
	// Check if timeout in nanoseconds would fit into an u64
	if (self.tv_nsec.0 as u64)
	.checked_add((self.tv_sec as u64).checked_mul(NSEC_PER_SEC)?)
	.is_none()
	{
	return None;
	}
	self.to_timespec()
	}

	#[cfg(all(
	target_os = "linux",
	target_env = "gnu",
	target_pointer_width = "32",
	not(target_arch = "riscv32")
	))]
	pub fn to_timespec64(&self) -> __timespec64 {
	__timespec64::new(self.tv_sec, self.tv_nsec.0 as _)
	}
	}

	impl From<libc::timespec> for Timespec {
	fn from(t: libc::timespec) -> Timespec {
	Timespec::new(t.tv_sec as i64, t.tv_nsec as i64)
	}
	}

	#[cfg(all(
	target_os = "linux",
	target_env = "gnu",
	target_pointer_width = "32",
	not(target_arch = "riscv32")
	))]
	#[repr(C)]
	pub(in crate::sys::unix) struct __timespec64 {
	pub(in crate::sys::unix) tv_sec: i64,
	#[cfg(target_endian = "big")]
	_padding: i32,
	pub(in crate::sys::unix) tv_nsec: i32,
	#[cfg(target_endian = "little")]
	_padding: i32,
	}

	#[cfg(all(
	target_os = "linux",
	target_env = "gnu",
	target_pointer_width = "32",
	not(target_arch = "riscv32")
	))]
	impl __timespec64 {
	pub(in crate::sys::unix) fn new(tv_sec: i64, tv_nsec: i32) -> Self {
	Self { tv_sec, tv_nsec, _padding: 0 }
	}
	}

	#[cfg(all(
	target_os = "linux",
	target_env = "gnu",
	target_pointer_width = "32",
	not(target_arch = "riscv32")
	))]
	impl From<__timespec64> for Timespec {
	fn from(t: __timespec64) -> Timespec {
	Timespec::new(t.tv_sec, t.tv_nsec.into())
	}
	}

	#[cfg(any(
	all(target_os = "macos", any(not(target_arch = "aarch64"))),
	target_os = "ios",
	target_os = "watchos"
	))]
	mod inner {
	use crate::sync::atomic::{AtomicU64, Ordering};
	use crate::sys::cvt;
	use crate::sys_common::mul_div_u64;
	use crate::time::Duration;

	use super::{SystemTime, Timespec, NSEC_PER_SEC};

	#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
	pub struct Instant {
	t: u64,
	}

	#[repr(C)]
	#[derive(Copy, Clone)]
	struct mach_timebase_info {
	numer: u32,
	denom: u32,
	}
	type mach_timebase_info_t = *mut mach_timebase_info;
	type kern_return_t = libc::c_int;

	impl Instant {
	pub fn now() -> Instant {
	extern "C" {
	fn mach_absolute_time() -> u64;
	}
	Instant { t: unsafe { mach_absolute_time() } }
	}

	pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
	let diff = self.t.checked_sub(other.t)?;
	let info = info();
	let nanos = mul_div_u64(diff, info.numer as u64, info.denom as u64);
	Some(Duration::new(nanos / NSEC_PER_SEC, (nanos % NSEC_PER_SEC) as u32))
	}

	pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
	Some(Instant { t: self.t.checked_add(checked_dur2intervals(other)?)? })
	}

	pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
	Some(Instant { t: self.t.checked_sub(checked_dur2intervals(other)?)? })
	}
	}

	impl SystemTime {
	pub fn now() -> SystemTime {
	use crate::ptr;

	let mut s = libc::timeval { tv_sec: 0, tv_usec: 0 };
	cvt(unsafe { libc::gettimeofday(&mut s, ptr::null_mut()) }).unwrap();
	return SystemTime::from(s);
	}
	}

	impl From<libc::timeval> for Timespec {
	fn from(t: libc::timeval) -> Timespec {
	Timespec::new(t.tv_sec as i64, 1000 * t.tv_usec as i64)
	}
	}

	impl From<libc::timeval> for SystemTime {
	fn from(t: libc::timeval) -> SystemTime {
	SystemTime { t: Timespec::from(t) }
	}
	}

	fn checked_dur2intervals(dur: &Duration) -> Option<u64> {
	let nanos =
	dur.as_secs().checked_mul(NSEC_PER_SEC)?.checked_add(dur.subsec_nanos() as u64)?;
	let info = info();
	Some(mul_div_u64(nanos, info.denom as u64, info.numer as u64))
	}

	fn info() -> mach_timebase_info {
	// INFO_BITS conceptually is an `Option<mach_timebase_info>`. We can do
	// this in 64 bits because we know 0 is never a valid value for the
	// `denom` field.
	//
	// Encoding this as a single `AtomicU64` allows us to use `Relaxed`
	// operations, as we are only interested in the effects on a single
	// memory location.
	static INFO_BITS: AtomicU64 = AtomicU64::new(0);

	// If a previous thread has initialized `INFO_BITS`, use it.
	let info_bits = INFO_BITS.load(Ordering::Relaxed);
	if info_bits != 0 {
	return info_from_bits(info_bits);
	}

	// ... otherwise learn for ourselves ...
	extern "C" {
	fn mach_timebase_info(info: mach_timebase_info_t) -> kern_return_t;
	}

	let mut info = info_from_bits(0);
	unsafe {
	mach_timebase_info(&mut info);
	}
	INFO_BITS.store(info_to_bits(info), Ordering::Relaxed);
	info
	}

	#[inline]
	fn info_to_bits(info: mach_timebase_info) -> u64 {
	((info.denom as u64) << 32) \| (info.numer as u64)
	}

	#[inline]
	fn info_from_bits(bits: u64) -> mach_timebase_info {
	mach_timebase_info { numer: bits as u32, denom: (bits >> 32) as u32 }
	}
	}

	#[cfg(not(any(
	all(target_os = "macos", any(not(target_arch = "aarch64"))),
	target_os = "ios",
	target_os = "watchos"
	)))]
	mod inner {
	use crate::fmt;
	use crate::mem::MaybeUninit;
	use crate::sys::cvt;
	use crate::time::Duration;

	use super::{SystemTime, Timespec};

	#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
	pub struct Instant {
	t: Timespec,
	}

	impl Instant {
	pub fn now() -> Instant {
	#[cfg(target_os = "macos")]
	const clock_id: libc::clockid_t = libc::CLOCK_UPTIME_RAW;
	#[cfg(not(target_os = "macos"))]
	const clock_id: libc::clockid_t = libc::CLOCK_MONOTONIC;
	Instant { t: Timespec::now(clock_id) }
	}

	pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
	self.t.sub_timespec(&other.t).ok()
	}

	pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
	Some(Instant { t: self.t.checked_add_duration(other)? })
	}

	pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
	Some(Instant { t: self.t.checked_sub_duration(other)? })
	}
	}

	impl fmt::Debug for Instant {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	f.debug_struct("Instant")
	.field("tv_sec", &self.t.tv_sec)
	.field("tv_nsec", &self.t.tv_nsec.0)
	.finish()
	}
	}

	impl SystemTime {
	pub fn now() -> SystemTime {
	SystemTime { t: Timespec::now(libc::CLOCK_REALTIME) }
	}
	}

	impl Timespec {
	pub fn now(clock: libc::clockid_t) -> Timespec {
	// Try to use 64-bit time in preparation for Y2038.
	#[cfg(all(
	target_os = "linux",
	target_env = "gnu",
	target_pointer_width = "32",
	not(target_arch = "riscv32")
	))]
	{
	use crate::sys::weak::weak;

	// __clock_gettime64 was added to 32-bit arches in glibc 2.34,
	// and it handles both vDSO calls and ENOSYS fallbacks itself.
	weak!(fn __clock_gettime64(libc::clockid_t, *mut super::__timespec64) -> libc::c_int);

	if let Some(clock_gettime64) = __clock_gettime64.get() {
	let mut t = MaybeUninit::uninit();
	cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
	return Timespec::from(unsafe { t.assume_init() });
	}
	}

	let mut t = MaybeUninit::uninit();
	cvt(unsafe { libc::clock_gettime(clock, t.as_mut_ptr()) }).unwrap();
	Timespec::from(unsafe { t.assume_init() })
	}
	}
	}