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.

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.

Installation

[dependencies]
fasttime = "0.1"

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 runs a Criterion benchmark that compares fasttime::DateTime::from_unix_timestamp with time::OffsetDateTime::from_unix_timestamp_nanos.

Example output

from_unix_timestamp/fasttime::DateTime
                        time:   [9.0027 µs 9.0169 µs 9.0311 µs]
Found 8 outliers among 100 measurements (8.00%)
  3 (3.00%) low mild
  4 (4.00%) high mild
  1 (1.00%) high severe
from_unix_timestamp/time::OffsetDateTime
                        time:   [11.872 µs 11.963 µs 12.077 µs]
Found 11 outliers among 100 measurements (11.00%)
  3 (3.00%) high mild
  8 (8.00%) high severe

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 License, Version 2.0 (see Cargo.toml metadata).