quanta

quanta is a high-speed timing library, useful for getting the current time very quickly, as well as manipulating
it.

code of conduct

NOTE: All conversations and contributions to this project shall adhere to the [Code of Conduct][conduct].

usage

The API documentation of this library can be found at docs.rs/quanta.

general features

  - count CPU cycles via Time Stamp Counter (TSC). or
  - get monotonic time, in nanoseconds, based on TSC (or OS fallback)
  - extremely low overhead where possible
  - mockable
  - cross-platform
  - fun, science-y name!

platform / architecture support

For most major platforms -- Linux, Windows, and macOS -- with processors made around or after 2008, you should have no
problems using quanta with full TSC support. quanta will always fallback to the included stdlib timing facilities if
TSC support is not present. The biggest caveat to this, as evidenced in the compatibility matrix below, is that we only
support the TSC on x86/x86_64 platforms.

| Platform             | stdlib fallback | TSC support? | CI tests? |
|----------------------|-----------------|--------------|-----------|
| Linux (x86/x86_64)   | ✅               | ✅           | ✅        |
| Linux (MIPS/ARM)     | ✅               | ❌           | ✅        |
| Windows (x86/x86_64) | ✅               | ✅           | ✅        |
| Windows (ARM)        | ✅               | ❌           | ❌        |
| macOS (x86/x86_64)   | ✅               | ✅           | ✅        |
| macOS (ARM)          | ✅               | ❌           | ❌        |
| iOS (ARM)            | ✅               | ❌           | ❌        |

performance

quanta sits neck-and-neck with native OS time facilities: the cost of Clock::now is on par Instant::now from the
stdlib, if not better.

why use this over stdlib?

Beyond having a performance edge in specific situations, the ability to use mocked time makes it easier to actually test
that your application is doing the right thing when time is involved.

Additionally, and as mentioned in the general features section, quanta provides a safe/thin wrapper over accessing the
Time Stamp Counter, which allows measuring cycle counts over short sections of code.  This can be relevant/important for
accurately measuring performance-critical sections of code.

alternative crates

  - chrono:
      - based on std::time::SystemTime: non-monotonic reads
      - focused on timezone-based "date/time" measurements, not intervals/elapsed time
      - clock cannot be altered at all (no pause, no discrete updates)
  - time:
      - based on std::time::SystemTime and std::time::Instant:
          - time::Time/time::PrimitiveDateTime use SystemTime: non-monotonic reads
          - time::Instant uses Instant: monotonic reads
      - focused on timezone-based "date/time" measurements, not interval/elapsed time
      - clock cannot be altered at all (no pause, no discrete updates)
  - clock:
      - based on std::time::SystemTime: non-monotonic reads
      - clock can be swapped (trait-based)
      - no free function for acquiring time
  - clocksource:
      - based on TSC w/ OS fallback; non-monotonic reads
      - clock cannot be altered at all (no pause, no discrete updates)
      - depends on unstable asm! macro + feature flag to enable TSC
      - no free function for acquiring time
  - pausable_clock:
      - based on std::time::Instant: monotonic reads
      - clock can be paused (time can be delayed, but not discretely updated)
      - no free function for acquiring time

license

quanta is licensed under the MIT license. (LICENSE or http://opensource.org/licenses/MIT)
