zx/
clock.rs

1// Copyright 2020 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5//! Type-safe bindings for Zircon clock objects.
6
7use crate::{
8    ok, sys, AsHandleRef, BootTimeline, ClockUpdate, Handle, HandleBased, HandleRef, Instant,
9    MonotonicTimeline, SyntheticTimeline, Timeline,
10};
11use bitflags::bitflags;
12use std::mem::MaybeUninit;
13use std::ptr;
14use zx_status::Status;
15
16/// An object representing a kernel [clock], used to track the progress of time. A clock is a
17/// one-dimensional affine transformation of the [clock monotonic] reference timeline which may be
18/// atomically adjusted by a maintainer and observed by clients.
19///
20/// As essentially a subtype of `Handle`, it can be freely interconverted.
21///
22/// [clock]: https://fuchsia.dev/fuchsia-src/reference/kernel_objects/clock
23/// [clock monotonic]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_get_monotonic.md
24#[derive(Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
25#[repr(transparent)]
26pub struct Clock<Reference = MonotonicTimeline, Output = SyntheticTimeline>(
27    Handle,
28    std::marker::PhantomData<(Reference, Output)>,
29);
30
31pub type SyntheticClock = Clock<MonotonicTimeline, SyntheticTimeline>;
32pub type SyntheticClockOnBoot = Clock<BootTimeline, SyntheticTimeline>;
33
34impl<Output: Timeline> Clock<MonotonicTimeline, Output> {
35    /// Create a new clock object with the provided arguments, with the monotonic clock as the
36    /// reference timeline. Wraps the [zx_clock_create] syscall.
37    ///
38    /// [zx_clock_create]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_create
39    pub fn create(opts: ClockOpts, backstop: Option<Instant<Output>>) -> Result<Self, Status> {
40        let mut out = 0;
41        let status = match backstop {
42            Some(backstop) => {
43                // When using backstop time, use the API v1 args struct.
44                let args = sys::zx_clock_create_args_v1_t { backstop_time: backstop.into_nanos() };
45                unsafe {
46                    sys::zx_clock_create(
47                        sys::ZX_CLOCK_ARGS_VERSION_1 | opts.bits(),
48                        std::ptr::from_ref(&args).cast::<u8>(),
49                        &mut out,
50                    )
51                }
52            }
53            None => unsafe { sys::zx_clock_create(opts.bits(), ptr::null(), &mut out) },
54        };
55        ok(status)?;
56        unsafe { Ok(Self::from(Handle::from_raw(out))) }
57    }
58}
59
60impl<Output: Timeline> Clock<BootTimeline, Output> {
61    /// Create a new clock object with the provided arguments, with the boot clock as the reference
62    /// timeline. Wraps the [zx_clock_create] syscall.
63    ///
64    /// [zx_clock_create]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_create
65    pub fn create(opts: ClockOpts, backstop: Option<Instant<Output>>) -> Result<Self, Status> {
66        let mut out = 0;
67        let opts = opts | ClockOpts::BOOT;
68        let status = match backstop {
69            Some(backstop) => {
70                // When using backstop time, use the API v1 args struct.
71                let args = sys::zx_clock_create_args_v1_t { backstop_time: backstop.into_nanos() };
72                unsafe {
73                    sys::zx_clock_create(
74                        sys::ZX_CLOCK_ARGS_VERSION_1 | opts.bits(),
75                        &args as *const _ as *const u8,
76                        &mut out,
77                    )
78                }
79            }
80            None => unsafe { sys::zx_clock_create(opts.bits(), ptr::null(), &mut out) },
81        };
82        ok(status)?;
83        unsafe { Ok(Self::from(Handle::from_raw(out))) }
84    }
85}
86
87impl<Reference: Timeline, Output: Timeline> Clock<Reference, Output> {
88    /// Perform a basic read of this clock. Wraps the [zx_clock_read] syscall. Requires
89    /// `ZX_RIGHT_READ` and that the clock has had an initial time established.
90    ///
91    /// [zx_clock_read]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_read
92    pub fn read(&self) -> Result<Instant<Output>, Status> {
93        let mut now = 0;
94        let status = unsafe { sys::zx_clock_read(self.raw_handle(), &mut now) };
95        ok(status)?;
96        Ok(Instant::<Output>::from_nanos(now))
97    }
98
99    /// Perform a basic read of a mapped clock. Wraps the [zx_clock_read_mapped] syscall.
100    ///
101    /// # Safety
102    ///
103    /// |zx_clock_get_details_mapped| must only be called using a |clock_addr| which is the address
104    /// of a clock's state currently mapped into the caller's address space using
105    /// |zx_vmar_map_clock|.  Attempting to get_details from any other address, or from a clock
106    /// mapping which has been unmapped (completely or partially) will result in undefined behavior.
107    ///
108    /// [zx_clock_read]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_read_mapped
109    pub unsafe fn read_mapped(clock_addr: *const u8) -> Result<Instant<Output>, Status> {
110        let mut now = 0;
111        let status = unsafe { sys::zx_clock_read_mapped(clock_addr, &mut now) };
112        ok(status)?;
113        Ok(Instant::<Output>::from_nanos(now))
114    }
115
116    /// Get low level details of this clock's current status. Wraps the
117    /// [zx_clock_get_details] syscall. Requires `ZX_RIGHT_READ`.
118    ///
119    /// [zx_clock_get_details]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_get_details
120    pub fn get_details(&self) -> Result<ClockDetails<Reference, Output>, Status> {
121        let mut out_details = MaybeUninit::<sys::zx_clock_details_v1_t>::uninit();
122        let status = unsafe {
123            sys::zx_clock_get_details(
124                self.raw_handle(),
125                sys::ZX_CLOCK_ARGS_VERSION_1,
126                out_details.as_mut_ptr().cast::<u8>(),
127            )
128        };
129        ok(status)?;
130        let out_details = unsafe { out_details.assume_init() };
131        Ok(out_details.into())
132    }
133
134    /// Get low level details of a mapped clock's current status. Wraps the
135    /// [zx_clock_get_details_mapped] syscall.
136    ///
137    /// # Safety
138    ///
139    /// |zx_clock_get_details_mapped| must only be called using a |clock_addr| which is the address
140    /// of a clock's state currently mapped into the caller's address space using
141    /// |zx_vmar_map_clock|.  Attempting to get_details from any other address, or from a clock
142    /// mapping which has been unmapped (completely or partially) will result in undefined behavior.
143    ///
144    /// [zx_clock_get_details_mapped]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_get_details_mapped
145    pub unsafe fn get_details_mapped(
146        clock_addr: *const u8,
147    ) -> Result<ClockDetails<Reference, Output>, Status> {
148        let mut out_details = MaybeUninit::<sys::zx_clock_details_v1_t>::uninit();
149        let status = unsafe {
150            sys::zx_clock_get_details_mapped(
151                clock_addr,
152                sys::ZX_CLOCK_ARGS_VERSION_1,
153                out_details.as_mut_ptr().cast::<u8>(),
154            )
155        };
156        ok(status)?;
157        let out_details = unsafe { out_details.assume_init() };
158        Ok(out_details.into())
159    }
160
161    /// Make adjustments to this clock. Wraps the [zx_clock_update] syscall. Requires
162    /// `ZX_RIGHT_WRITE`.
163    ///
164    /// [zx_clock_update]: https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_update
165    pub fn update(&self, update: impl Into<ClockUpdate<Reference, Output>>) -> Result<(), Status> {
166        let update = update.into();
167        let options = update.options();
168        let args = update.args();
169        let status = unsafe {
170            sys::zx_clock_update(self.raw_handle(), options, std::ptr::from_ref(&args).cast::<u8>())
171        };
172        ok(status)?;
173        Ok(())
174    }
175
176    /// Convert this clock to one on a generic synthetic timeline, erasing any user-defined
177    /// timeline.
178    pub fn downcast<NewReference: Timeline>(self) -> Clock<NewReference, SyntheticTimeline> {
179        Clock(self.0, std::marker::PhantomData)
180    }
181}
182
183impl<Reference: Timeline> Clock<Reference, SyntheticTimeline> {
184    /// Cast a "base" clock to one with a user-defined timeline that will carry the timeline for
185    /// all transformations and reads.
186    pub fn cast<NewReference: Timeline, UserTimeline: Timeline>(
187        self,
188    ) -> Clock<NewReference, UserTimeline> {
189        Clock(self.0, std::marker::PhantomData)
190    }
191}
192
193impl<Reference: Timeline, Output: Timeline> AsHandleRef for Clock<Reference, Output> {
194    fn as_handle_ref(&self) -> HandleRef<'_> {
195        self.0.as_handle_ref()
196    }
197}
198
199impl<Reference: Timeline, Output: Timeline> From<Handle> for Clock<Reference, Output> {
200    fn from(handle: Handle) -> Self {
201        Clock(handle, std::marker::PhantomData)
202    }
203}
204
205impl<Reference: Timeline, Output: Timeline> From<Clock<Reference, Output>> for Handle {
206    fn from(x: Clock<Reference, Output>) -> Handle {
207        x.0
208    }
209}
210
211impl<Reference: Timeline, Output: Timeline> HandleBased for Clock<Reference, Output> {}
212
213bitflags! {
214    #[repr(transparent)]
215    #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
216    pub struct ClockOpts: u64 {
217        /// When set, creates a clock object which is guaranteed to never run backwards. Monotonic
218        /// clocks must always move forward.
219        const MONOTONIC = sys::ZX_CLOCK_OPT_MONOTONIC;
220
221        /// When set, creates a clock which is guaranteed to never jump either forwards or
222        /// backwards. Continuous clocks may only be maintained using frequency adjustments and are,
223        /// by definition, also monotonic.
224        const CONTINUOUS = sys::ZX_CLOCK_OPT_CONTINUOUS | Self::MONOTONIC.bits();
225
226        /// When set, creates a clock that is automatically started and is initially a clone of
227        /// clock monotonic. Users may still update the clock within the limits defined by the
228        /// other options, the handle rights, and the backstop time of the clock.
229        const AUTO_START = sys::ZX_CLOCK_OPT_AUTO_START;
230
231        /// When set, creates a clock object that uses the boot timeline as its reference timeline.
232        const BOOT = sys::ZX_CLOCK_OPT_BOOT;
233
234        /// When set, creates a clock whose state may be mapped into a VMAR, allowing the state to
235        /// be used with calls to |zx_clock_read_mapped| and |zx_clock_get_details_mapped|.
236        const MAPPABLE = sys::ZX_CLOCK_OPT_MAPPABLE;
237    }
238}
239
240/// Fine grained details of a [`Clock`] object.
241#[derive(Debug, Clone, PartialEq, Eq)]
242pub struct ClockDetails<Reference = MonotonicTimeline, Output = SyntheticTimeline> {
243    /// The minimum time the clock can ever be set to.
244    pub backstop: Instant<Output>,
245
246    /// The current ticks to clock transformation.
247    pub ticks_to_synthetic: ClockTransformation<Reference, Output>,
248
249    /// The current clock monotonic to clock transformation.
250    pub reference_to_synthetic: ClockTransformation<Reference, Output>,
251
252    /// The current symmetric error estimate (if any) for the clock, measured in nanoseconds.
253    pub error_bounds: u64,
254
255    /// An observation of the system tick counter which was taken during the observation of the
256    /// clock.
257    pub query_ticks: sys::zx_ticks_t,
258
259    /// The last time the clock's value was updated as defined by the clock monotonic reference
260    /// timeline.
261    pub last_value_update_ticks: sys::zx_ticks_t,
262
263    /// The last time the clock's rate adjustment was updated as defined by the clock monotonic
264    /// reference timeline.
265    pub last_rate_adjust_update_ticks: sys::zx_ticks_t,
266
267    /// The last time the clock's error bounds were updated as defined by the clock monotonic
268    /// reference timeline.
269    pub last_error_bounds_update_ticks: sys::zx_ticks_t,
270
271    /// The generation nonce.
272    pub generation_counter: u32,
273}
274
275impl<Reference: Timeline, Output: Timeline> From<sys::zx_clock_details_v1_t>
276    for ClockDetails<Reference, Output>
277{
278    fn from(details: sys::zx_clock_details_v1_t) -> Self {
279        ClockDetails {
280            backstop: Instant::from_nanos(details.backstop_time),
281            ticks_to_synthetic: details.reference_ticks_to_synthetic.into(),
282            reference_to_synthetic: details.reference_to_synthetic.into(),
283            error_bounds: details.error_bound,
284            query_ticks: details.query_ticks,
285            last_value_update_ticks: details.last_value_update_ticks,
286            last_rate_adjust_update_ticks: details.last_rate_adjust_update_ticks,
287            last_error_bounds_update_ticks: details.last_error_bounds_update_ticks,
288            generation_counter: details.generation_counter,
289        }
290    }
291}
292
293/// A one-dimensional affine transformation that maps points from the reference timeline to the
294/// clock timeline. See [clock transformations].
295///
296/// [clock transformations]: https://fuchsia.dev/fuchsia-src/concepts/kernel/clock_transformations
297#[derive(Debug, Clone, Eq, PartialEq)]
298pub struct ClockTransformation<Reference = MonotonicTimeline, Output = SyntheticTimeline> {
299    /// The offset on the reference timeline, measured in reference clock ticks.
300    pub reference_offset: Instant<Reference>,
301    /// The offset on the clock timeline, measured in clock ticks (typically normalized to
302    /// nanoseconds).
303    pub synthetic_offset: Instant<Output>,
304    /// The ratio of the reference to clock rate.
305    pub rate: sys::zx_clock_rate_t,
306}
307
308impl<Reference: Timeline, Output: Timeline> From<sys::zx_clock_transformation_t>
309    for ClockTransformation<Reference, Output>
310{
311    fn from(ct: sys::zx_clock_transformation_t) -> Self {
312        ClockTransformation {
313            reference_offset: Instant::<Reference>::from_nanos(ct.reference_offset),
314            synthetic_offset: Instant::<Output>::from_nanos(ct.synthetic_offset),
315            rate: ct.rate,
316        }
317    }
318}
319
320/// Apply affine transformation to convert the reference time "r" to the synthetic time
321/// "c". All values are widened to i128 before calculations and the end result is converted back to
322/// a i64. If "c" is a larger number than would fit in an i64, the result saturates when cast to
323/// i64.
324fn transform_clock(r: i64, r_offset: i64, c_offset: i64, r_rate: u32, c_rate: u32) -> i64 {
325    let r = r as i128;
326    let r_offset = r_offset as i128;
327    let c_offset = c_offset as i128;
328    let r_rate = r_rate as i128;
329    let c_rate = c_rate as i128;
330    let c = (((r - r_offset) * c_rate) / r_rate) + c_offset;
331    c.try_into().unwrap_or_else(|_| if c.is_positive() { i64::MAX } else { i64::MIN })
332}
333
334/// [Clock transformations](https://fuchsia.dev/fuchsia-src/concepts/kernel/clock_transformations)
335/// can be applied to convert a time from a reference time to a synthetic time. The inverse
336/// transformation can be applied to convert a synthetic time back to the reference time.
337impl<Reference: Timeline + Copy, Output: Timeline + Copy> ClockTransformation<Reference, Output> {
338    pub fn apply(&self, time: Instant<Reference>) -> Instant<Output> {
339        let c = transform_clock(
340            time.into_nanos(),
341            self.reference_offset.into_nanos(),
342            self.synthetic_offset.into_nanos(),
343            self.rate.reference_ticks,
344            self.rate.synthetic_ticks,
345        );
346
347        Instant::from_nanos(c)
348    }
349
350    pub fn apply_inverse(&self, time: Instant<Output>) -> Instant<Reference> {
351        let r = transform_clock(
352            time.into_nanos(),
353            self.synthetic_offset.into_nanos(),
354            self.reference_offset.into_nanos(),
355            self.rate.synthetic_ticks,
356            self.rate.reference_ticks,
357        );
358
359        Instant::from_nanos(r as i64)
360    }
361}
362
363#[cfg(test)]
364mod tests {
365    use super::*;
366    use crate::{MonotonicInstant, SyntheticInstant};
367    use assert_matches::assert_matches;
368
369    #[test]
370    fn create_clocks() {
371        assert_matches!(SyntheticClock::create(ClockOpts::empty(), None), Ok(_));
372        assert_matches!(SyntheticClock::create(ClockOpts::MONOTONIC, None), Ok(_));
373        assert_matches!(SyntheticClock::create(ClockOpts::CONTINUOUS, None), Ok(_));
374        assert_matches!(
375            SyntheticClock::create(ClockOpts::AUTO_START | ClockOpts::MONOTONIC, None),
376            Ok(_)
377        );
378        assert_matches!(
379            SyntheticClock::create(ClockOpts::AUTO_START | ClockOpts::CONTINUOUS, None),
380            Ok(_)
381        );
382
383        // Now with backstop.
384        let backstop = Some(SyntheticInstant::from_nanos(5500));
385        assert_matches!(SyntheticClock::create(ClockOpts::MONOTONIC, backstop), Ok(_));
386        assert_matches!(SyntheticClock::create(ClockOpts::CONTINUOUS, backstop), Ok(_));
387        assert_matches!(
388            SyntheticClock::create(ClockOpts::AUTO_START | ClockOpts::MONOTONIC, backstop),
389            Ok(_)
390        );
391        assert_matches!(
392            SyntheticClock::create(ClockOpts::AUTO_START | ClockOpts::CONTINUOUS, backstop),
393            Ok(_)
394        );
395    }
396
397    #[test]
398    fn read_time() {
399        let clock =
400            SyntheticClock::create(ClockOpts::MONOTONIC, None).expect("failed to create clock");
401        assert_matches!(clock.read(), Ok(_));
402    }
403
404    #[test]
405    fn get_clock_details() {
406        // No backstop.
407        let clock =
408            SyntheticClock::create(ClockOpts::MONOTONIC, None).expect("failed to create clock");
409        let details = clock.get_details().expect("failed to get details");
410        assert_eq!(details.backstop, SyntheticInstant::from_nanos(0));
411
412        // With backstop.
413        let clock =
414            SyntheticClock::create(ClockOpts::MONOTONIC, Some(SyntheticInstant::from_nanos(5500)))
415                .expect("failed to create clock");
416        let details = clock.get_details().expect("failed to get details");
417        assert_eq!(details.backstop, SyntheticInstant::from_nanos(5500));
418    }
419
420    #[test]
421    fn update_clock() {
422        let clock =
423            SyntheticClock::create(ClockOpts::MONOTONIC, None).expect("failed to create clock");
424        let before_details = clock.get_details().expect("failed to get details");
425        assert_eq!(before_details.last_value_update_ticks, 0);
426        assert_eq!(before_details.last_rate_adjust_update_ticks, 0);
427        assert_eq!(before_details.last_error_bounds_update_ticks, 0);
428
429        // Update all properties.
430        clock
431            .update(
432                ClockUpdate::builder()
433                    .absolute_value(
434                        MonotonicInstant::from_nanos(999),
435                        SyntheticInstant::from_nanos(42),
436                    )
437                    .rate_adjust(52)
438                    .error_bounds(52),
439            )
440            .expect("failed to update clock");
441        let after_details = clock.get_details().expect("failed to get details");
442        assert!(before_details.generation_counter < after_details.generation_counter);
443        assert!(after_details.last_value_update_ticks > before_details.last_value_update_ticks);
444        assert_eq!(
445            after_details.last_value_update_ticks,
446            after_details.last_rate_adjust_update_ticks
447        );
448        assert_eq!(
449            after_details.last_value_update_ticks,
450            after_details.last_error_bounds_update_ticks
451        );
452        assert_eq!(after_details.error_bounds, 52);
453        assert_eq!(after_details.ticks_to_synthetic.synthetic_offset.into_nanos(), 42);
454        assert_eq!(after_details.reference_to_synthetic.reference_offset.into_nanos(), 999);
455        assert_eq!(after_details.reference_to_synthetic.synthetic_offset.into_nanos(), 42);
456
457        let before_details = after_details;
458
459        // Update only one property.
460        clock.update(ClockUpdate::builder().error_bounds(100)).expect("failed to update clock");
461        let after_details = clock.get_details().expect("failed to get details");
462        assert!(before_details.generation_counter < after_details.generation_counter);
463        assert!(
464            after_details.last_error_bounds_update_ticks > before_details.last_value_update_ticks
465        );
466        assert!(
467            after_details.last_error_bounds_update_ticks
468                > after_details.last_rate_adjust_update_ticks
469        );
470        assert_eq!(
471            after_details.last_rate_adjust_update_ticks,
472            after_details.last_value_update_ticks
473        );
474        assert_eq!(after_details.error_bounds, 100);
475        assert_eq!(after_details.ticks_to_synthetic.synthetic_offset.into_nanos(), 42);
476        assert_eq!(after_details.reference_to_synthetic.synthetic_offset.into_nanos(), 42);
477    }
478
479    #[test]
480    fn clock_identity_transformation_roundtrip() {
481        let t_0 = MonotonicInstant::ZERO;
482        // Identity clock transformation
483        let xform = ClockTransformation {
484            reference_offset: MonotonicInstant::from_nanos(0),
485            synthetic_offset: SyntheticInstant::from_nanos(0),
486            rate: sys::zx_clock_rate_t { synthetic_ticks: 1, reference_ticks: 1 },
487        };
488
489        // Transformation roundtrip should be equivalent with the identity transformation.
490        let transformed_time = xform.apply(t_0);
491        let original_time = xform.apply_inverse(transformed_time);
492        assert_eq!(t_0, original_time);
493    }
494
495    #[test]
496    fn clock_trivial_transformation() {
497        let t_0 = MonotonicInstant::ZERO;
498        // Identity clock transformation
499        let xform = ClockTransformation {
500            reference_offset: MonotonicInstant::from_nanos(3),
501            synthetic_offset: SyntheticInstant::from_nanos(2),
502            rate: sys::zx_clock_rate_t { synthetic_ticks: 6, reference_ticks: 2 },
503        };
504
505        let utc_time = xform.apply(t_0);
506        let monotonic_time = xform.apply_inverse(utc_time);
507        // Verify that the math is correct.
508        assert_eq!(3 * (t_0.into_nanos() - 3) + 2, utc_time.into_nanos());
509
510        // Transformation roundtrip should be equivalent.
511        assert_eq!(t_0, monotonic_time);
512    }
513
514    #[test]
515    fn clock_transformation_roundtrip() {
516        let t_0 = MonotonicInstant::ZERO;
517        // Arbitrary clock transformation
518        let xform = ClockTransformation {
519            reference_offset: MonotonicInstant::from_nanos(196980085208),
520            synthetic_offset: SyntheticInstant::from_nanos(1616900096031887801),
521            rate: sys::zx_clock_rate_t { synthetic_ticks: 999980, reference_ticks: 1000000 },
522        };
523
524        // Transformation roundtrip should be equivalent modulo rounding error.
525        let transformed_time = xform.apply(t_0);
526        let original_time = xform.apply_inverse(transformed_time);
527        let roundtrip_diff = t_0 - original_time;
528        assert!(roundtrip_diff.into_nanos().abs() <= 1);
529    }
530
531    #[test]
532    fn clock_trailing_transformation_roundtrip() {
533        let t_0 = MonotonicInstant::ZERO;
534        // Arbitrary clock transformation where the synthetic clock is trailing behind the
535        // reference clock.
536        let xform = ClockTransformation {
537            reference_offset: MonotonicInstant::from_nanos(1616900096031887801),
538            synthetic_offset: SyntheticInstant::from_nanos(196980085208),
539            rate: sys::zx_clock_rate_t { synthetic_ticks: 1000000, reference_ticks: 999980 },
540        };
541
542        // Transformation roundtrip should be equivalent modulo rounding error.
543        let transformed_time = xform.apply(t_0);
544        let original_time = xform.apply_inverse(transformed_time);
545        let roundtrip_diff = t_0 - original_time;
546        assert!(roundtrip_diff.into_nanos().abs() <= 1);
547    }
548
549    #[test]
550    fn clock_saturating_transformations() {
551        let t_0 = MonotonicInstant::from_nanos(i64::MAX);
552        // Clock transformation which will positively overflow t_0
553        let xform = ClockTransformation {
554            reference_offset: MonotonicInstant::from_nanos(0),
555            synthetic_offset: SyntheticInstant::from_nanos(1),
556            rate: sys::zx_clock_rate_t { synthetic_ticks: 1, reference_ticks: 1 },
557        };
558
559        // Applying the transformation will lead to saturation
560        let time = xform.apply(t_0).into_nanos();
561        assert_eq!(time, i64::MAX);
562
563        let t_0 = MonotonicInstant::from_nanos(i64::MIN);
564        // Clock transformation which will negatively overflow t_0
565        let xform = ClockTransformation {
566            reference_offset: MonotonicInstant::from_nanos(1),
567            synthetic_offset: SyntheticInstant::from_nanos(0),
568            rate: sys::zx_clock_rate_t { synthetic_ticks: 1, reference_ticks: 1 },
569        };
570
571        // Applying the transformation will lead to saturation
572        let time = xform.apply(t_0).into_nanos();
573        assert_eq!(time, i64::MIN);
574    }
575}
zx/clock.rs

zx/
clock.rs
