fasttime

fasttime is a small UTC-focused date/time library for Rust. It is built around Ben Joffe's constant-time 64-bit days→date algorithm and offers a simple, no_std-friendly API for calendar math, parsing, and formatting. The crate only depends on core by default and enables a handful of conveniences (such as DateTime::now_utc()) when the optional std feature is on.

🐍 Python bindings are now available! See python/README.md for details.

Features

• Works in no_std environments; opt into std when you need wall-clock time.
• Date, Time, DateTime, Duration, UtcOffset, and OffsetDateTime types with ISO/RFC 3339 style Display implementations.
• Parsing helpers for the common textual formats used in logs and APIs.
• Fixed-offset RFC 3339 timestamps with nanosecond precision.
• Simple arithmetic helpers: add days, add durations, compute differences, and fetch ordinals or weekdays without extra allocations.
• Python 3.10+ bindings via PyO3 with full type hints and ergonomic API.

Installation

Rust

[dependencies]
fasttime = "0.2"

Python

pip install maturin
maturin develop --release

Disable the default std feature when targeting bare-metal or embedded environments:

[dependencies]
fasttime = { version = "0.1", default-features = false }

Example

use fasttime::{
    Date, DateError, DateTime, Duration, OffsetDateTime, Time, UtcOffset,
};

fn main() -> Result<(), DateError> {
    // Fetch the current UTC date and time, works only with `std` feature.
    // let now = DateTime::now_utc()?;
    // println!("Current UTC time: {now}");

    // Build calendar dates either from year-month-day or days since the Unix epoch.
    let jan_first = Date::from_ymd(2024, 1, 1)?;
    let epoch = Date::from_days_since_unix_epoch(0)?;
    println!("{jan_first} weekday {}", jan_first.weekday().number_from_monday());
    println!("{epoch} ordinal {}", epoch.ordinal());

    // Combine dates and times to work with UTC instants.
    let dt = DateTime::from_unix_timestamp(1_700_000_000, 123_456_789)?;
    let later = dt.add_duration(Duration::seconds(90))?;
    println!("Delta: {} ns", later.difference(dt).total_nanos());

    // Parse ISO/RFC 3339 style strings and work with fixed offsets.
    let parsed_date: Date = "2024-03-15".parse()?;
    let parsed_time: Time = "11:22:33.123".parse().unwrap();
    let offset = UtcOffset::from_hours_minutes(true, 2, 0).unwrap();
    let local = OffsetDateTime::from_local(parsed_date, parsed_time, offset)?;
    println!("{local} (offset {})", offset);

    Ok(())
}

Benchmarks

cargo bench --bench unix_timestamp -- --quick runs a quick benchmark comparing fasttime's Unix timestamp conversions to the widely used time crate.

The benchmark covers three operations:

• from_unix_timestamp: constructor taking (secs, nanos).
• to_unix_timestamp: extracting integral seconds.
• to_unix_timestamp_nanos: extracting nanoseconds as i128.

Example output

from_unix_timestamp/fasttime::default-n=1024
                        time:   [6.3651 µs 6.3674 µs 6.3765 µs]
                        change: [+0.0149% +0.2131% +0.4118%] (p = 0.14 > 0.05)
                        No change in performance detected.
from_unix_timestamp/time::default-n=1024
                        time:   [8.6900 µs 8.6924 µs 8.7022 µs]
                        change: [+3.0617% +3.2376% +3.4139%] (p = 0.10 > 0.05)
                        No change in performance detected.

to_unix_timestamp/fasttime::default-n=1024
                        time:   [1.6843 µs 1.6853 µs 1.6894 µs]
                        change: [−1.1021% −0.5719% −0.0376%] (p = 0.10 > 0.05)
                        No change in performance detected.
to_unix_timestamp/time::default-n=1024
                        time:   [1.8566 µs 1.8589 µs 1.8682 µs]
                        change: [−0.0414% +0.3413% +0.7245%] (p = 0.33 > 0.05)
                        No change in performance detected.

to_unix_timestamp_nanos/fasttime::default-n=1024
                        time:   [2.0008 µs 2.0063 µs 2.0077 µs]
                        change: [−0.0852% +0.2399% +0.5661%] (p = 0.33 > 0.05)
                        No change in performance detected.
to_unix_timestamp_nanos/time::default-n=1024
                        time:   [2.0863 µs 2.0880 µs 2.0946 µs]
                        change: [+0.4222% +0.7240% +1.0265%] (p = 0.08 > 0.05)
                        No change in performance detected.

Conclusion

In this sample run, fasttime is consistently faster than time for all three timestamp operations (about 27% faster for from_unix_timestamp, about 9% faster for to_unix_timestamp, and about 4% faster for to_unix_timestamp_nanos), while all comparisons report no statistically significant regression versus baseline.

Development

• Format and lint the crate with your preferred Rust tooling (cargo fmt, cargo clippy).
• Run the tests with cargo test.

License

Licensed under the Apache-2.0