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A high fidelity time management library in Rust
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hifitime 1.0

Precise date and time handling in Rust built on top of std::f64. The Epoch used is TAI Epoch of 01 Jan 1900 at midnight, but that should not matter in day-to-day use of this library.

Build Status hifitime on hifitime on


  • Leap seconds (as announced by the IETF on a yearly basis)
  • Julian dates and Modified Julian dates
  • Clock drift via oscillator stability for simulation of time measuring hardware (via the simulation feature)
  • TODO: UTC representation with ISO8601 formatting (and parsing in that format #45)
  • Support for custom representations of time (e.g. NASA GMAT Modified Julian Date)
  • Trivial support of other time representations, such as TDT (cf #44)

Almost all examples are validated with external references, as detailed on a test-by-test basis.

Leap second support

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.


version 1.0 - COMPLETE rewrite

The previous API is totally incompatible with version 1.0.

In this new version:

  • Correct and explicit support for TAI versus UTC (previously, UTC was implied in the Datetime struct and TAI was implied in the Instant struct)
  • Removed annoyingly high precision which prevented simple day-to-day operations on seconds (as needed in most time simulation software)


After using this extensively for a few months, I've come to realize that it was highly ambiguous, and frankly a pain in the neck to use because of the complexity of the Instant struct. It made common operations complicated for no good reason. And at least one major bug existed (the difference between two Instant of MJD was different from the actual difference of MJDs converted to seconds).

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