Scientifically accurate date and time handling with guaranteed nanosecond precision for 32,768 years before 01 January 1900 and 32,767 years after that reference epoch.
2.hours() + 3.seconds()), subtraction (e.g. 2.hours() - 3.seconds()), round/floor/ceil operations (e.g. 2.hours().round(3.seconds()))Epochs and Durations)no-std and const fn where possibleAlmost all examples are validated with external references, as detailed on a test-by-test basis.
Epoch::{at_midnight, at_noon} is provided as a helper function.Put this in your Cargo.toml:
toml
[dependencies]
hifitime = "3.2"
And add the following to your crate root:
rust
extern crate hifitime;
```rust use hifitime::{Epoch, Unit, TimeUnits};
{ // Initialization from system time is only availble when std feature is enabled let now = Epoch::now().unwrap(); println!("{}", now); }
let mut santa = Epoch::fromgregorianutchms(2017, 12, 25, 01, 02, 14); asserteq!(santa.asmjdutcdays(), 58112.043217592590); asserteq!(santa.asjdeutc_days(), 2458112.5432175924);
asserteq!( santa + 3600 * Unit::Second, Epoch::fromgregorianutchms(2017, 12, 25, 02, 02, 14), "Could not add one hour to Christmas" );
asserteq!( santa + 60.0.minutes(), Epoch::fromgregorianutchms(2017, 12, 25, 02, 02, 14), "Could not add one hour to Christmas" );
asserteq!( santa + 1.hours(), Epoch::fromgregorianutchms(2017, 12, 25, 02, 02, 14), "Could not add one hour to Christmas" );
{ use std::str::FromStr; let dt = Epoch::fromgregorianutchms(2017, 1, 14, 0, 31, 55); asserteq!(dt, Epoch::fromstr("2017-01-14T00:31:55 UTC").unwrap()); // And you can print it too, although by default it will print in UTC asserteq!(dt.asgregorianutcstr(), "2017-01-14T00:31:55 UTC".tostring()); asserteq!(format!("{}", dt), "2017-01-14T00:31:55 UTC".tostring()); } ```
Comparing times will lead to a Duration type. Printing that will automatically select the unit. ```rust use hifitime::{Epoch, Unit, Duration, TimeUnits};
let atmidnight = Epoch::fromgregorianutcatmidnight(2020, 11, 2); let atnoon = Epoch::fromgregorianutcatnoon(2020, 11, 2); asserteq!(atnoon - atmidnight, 12 * Unit::Hour); asserteq!(atnoon - atmidnight, 1 * Unit::Day / 2); asserteq!(atmidnight - at_noon, -1.days() / 2);
let deltatime = atnoon - atmidnight; // asserteq!(format!("{}", deltatime), "12 h 0 min 0 s".tostring()); // And we can multiply durations by a scalar... let delta2 = 2 * deltatime; // asserteq!(format!("{}", delta2), "1 days 0 h 0 min 0 s".tostring()); // Or divide them by a scalar. // asserteq!(format!("{}", delta2 / 2.0), "12 h 0 min 0 s".to_string());
// And of course, these comparisons account for differences in time systems let atmidnightutc = Epoch::fromgregorianutcatmidnight(2020, 11, 2); let atnoontai = Epoch::fromgregoriantaiatnoon(2020, 11, 2); // asserteq!(format!("{}", atnoontai - atmidnightutc), "11 h 59 min 23 s".tostring()); ```
Timeunits and frequency units are trivially supported. Hifitime only supports up to nanosecond precision (but guarantees it for 64 millenia), so any duration less than one nanosecond is truncated.
```rust use hifitime::{Epoch, Unit, Freq, Duration, TimeUnits};
// One can compare durations assert!(10.seconds() > 5.seconds()); assert!(10.days() + 1.nanoseconds() > 10.days());
// Those durations are more precise than floating point since this is integer math in nanoseconds let d: Duration = 1.0.hours() / 3 - 20.minutes(); assert!(d.abs() < Unit::Nanosecond); assert_eq!(3 * 20.minutes(), Unit::Hour);
// And also frequencies but note that frequencies are converted to Durations! // So the duration of that frequency is compared, hence the following: assert!(10 * Freq::Hertz < 5 * Freq::Hertz); assert!(4 * Freq::MegaHertz > 5 * Freq::MegaHertz);
// And asserts on the units themselves assert!(Freq::GigaHertz < Freq::MegaHertz); assert!(Unit::Second > Unit::Millisecond); ```
Finally, something which may come in very handy, line spaces between times with a given step.
rust
use hifitime::{Epoch, Unit, TimeSeries};
let start = Epoch::from_gregorian_utc_at_midnight(2017, 1, 14);
let end = Epoch::from_gregorian_utc_at_noon(2017, 1, 14);
let step = 2 * Unit::Hour;
let time_series = TimeSeries::inclusive(start, end, step);
let mut cnt = 0;
for epoch in time_series {
println!("{}", epoch);
cnt += 1
}
// Check that there are indeed six two-hour periods in a half a day,
// including start and end times.
assert_eq!(cnt, 7)
Validation is done using NASA's SPICE toolkit, and specifically the spiceypy Python wrapper.
The most challenging validation is the definition of Ephemeris Time, which is very nearly the same as the Dynamic Barycentric Time (TDB). These calculations in hifitime are from ESA's Navipedia.
Hifitime uses a fixed offset for the computation of Ephemeris Time, as is recommended in Navipedia. For TDB however, the offset is based on the centuries since J2000 TT and therefore time varying. I believe that SPICE uses TDB for all dates after J2000 TT. Hence, in the following validation, we will be comparing the SPICE ET with the Hifitime TDB.
The following examples are executed as part of the standard test suite (cf. the function called spice_et_tdb).
Note: the differences shown here are likely due to a combination of SPICE using a different formulation for the calculation (using the constants in the SPICE kernels) and computing everything on a 64-bit floating point value. By design, a 64-bit floating point value has approximation errors. Hifitime performs all calculations on integers, which do not suffer from rounding errors.
In SPICE, we chose to convert the UTC date 2012-02-07 11:22:33 UTC into Ephemeris Time. SPICE responds with 381885819.18493587.
Initializing the same UTC date in hifitime and requesting the TDB leads to 381885819.18493646, which is an error of 596.05 nanoseconds.
In SPICE, we chose to convert the UTC date 2002-02-07 00:00:00.000 UTC into Ephemeris Time. SPICE responds with 66312064.18493876.
Initializing the same UTC date in hifitime and requesting the TDB leads to a difference 633.29 nanoseconds.
This tests that we can correctly compute TDB time which will have a negative number of days because the UTC input is prior to J2000 TT.
In SPICE, we chose to convert the UTC date 1996-02-07 11:22:33 UTC into Ephemeris Time. SPICE responds with -123035784.81506048.
Initializing the same UTC date in hifitime and requesting the TDB leads to a difference 640.74 nanoseconds.
In SPICE, we chose to convert the UTC date 2015-02-07 00:00:00.000 UTC into Ephemeris Time. SPICE responds with 476580220.1849411.
Initializing the same UTC date in hifitime and requesting the TDB leads to a difference 655.65 nanoseconds.
In SPICE, we chose to convert the TDB Julian Date in days 2452312.500372511 into Ephemeris Time, and initialize a Hifitime Epoch with that result (66312032.18493909).
We then convert that epoch back into days of Julian Date TDB and Julian Date ET, which lead a difference below machine precision for the TDB computation and 0.46 nanoseconds for the ET computation on a 64-bit floating point (f64/double).
Please report and bugs by clicking here.
Each time computing library may decide when the extra leap second exists as explained
in the IETF leap second reference.
To ease computation, hifitime decides that second is the 60th of a UTC date, if such exists.
Note that this second exists at a different time than defined on NASA HEASARC. That tool is
used for validation of Julian dates. As an example of how this is handled, check the Julian
day computations for 2015-06-30 23:59:59,
2015-06-30 23:59:60 and 2015-07-01 00:00:00.
ET and TDB should now be identical. However, hifitime uses the European Space Agency's definition of TDB, detailed here. It seems that SPICE uses the older definition which has a fixed offset from TDT of 0.000935 seconds. This difference is more prominent around the TDB epoch of 01 January 2000.
libm for non-core f64 operationsEq and some derive Ord (where relevant) #118Duration and Epoch, respectively with toparts and totai_parts #122Add ceil, floor, round operations to Epoch and Duration
Add #![no_std] support
to_parts to Duration to extract the centuries and nanoseconds of a durationEpoch from its duration and parts in TAI systemAdd pure nanosecond (u64) constructor and getter for GPST since GPS based clocks will count in nanoseconds
Errors::ParseError no longer contains a String but an enum ParsingErrors instead. This is considered possibly breaking because it would only break code in the cases where a datetime parsing or unit parsing was caught and handled (uncommon). Moreover, the output is still Display-able.
Backend rewritten from TwoFloat to a struct of the centuries in i16 and nanoseconds in u64. Thanks to @pwnorbitals for proposing the idea in #107 and writing the proof of concept. This leads to at least a 2x speed up in most calculations, cf. this comment.
Epoch by @cjordanas_jde_tdb_days() in Epoch. In version 2.2.1, the ephemeris time and TDB days were identical down to machine precision. After a number of validation cases in the rotation equations of the IAU Earth to Earth Mean Equator J2000 frame, the new formulation was shown to lead to less rounding errors when requesting the days. These rounding errors prevented otherwise trivial test cases. However, it adds an error of 40.2 nanoseconds when initializing an Epoch with the days in ET and requesting the TDB days.Note: this was originally published as 2.2.2 but I'd forgotten to update one of the tests with the 40.2 ns error.