human_format

Rust Port of human-format from node, formatting numbers for us, while the machines are still at bay.

Main	Develop

human_format is a small Rust library that makes numbers easier for people to read. It converts large or small numbers into short strings, like turning 1_000_000 into "1.00 M".

What it does

• Formats numbers with familiar suffixes: k, M, G, and so on.
• Parses human-friendly strings back into numbers with try_parse.
• Supports the newest SI prefixes (R, Q, r, q).
• Accepts and (optionally) outputs the micro sign µ.
• Lets you force a specific suffix for output (for example, always show values in M).
• Includes a Scales::Time() option for common time units (seconds, minutes, hours, days, months, years, quarters, centuries, etc.).

Quick start

Add the crate:

cargo add human_format

Use the formatter:

use human_format::Formatter;

// Default SI formatting
let s = Formatter::new().format(1000.0);
assert_eq!(s, "1.00 k");

// Control decimals
let s = Formatter::new().with_decimals(1).format(1337.0);
assert_eq!(s, "1.3 k");

Use binary scales (base 1024):

use human_format::{Formatter, Scales};
let s = Formatter::new().with_scales(Scales::Binary()).format(1024.0);
assert_eq!(s, "1.00 ki");

Parsing strings

Convert a human-friendly string back to a f64 with try_parse.

use human_format::{Formatter, Scales};

let f = Formatter::new();

assert_eq!(f.try_parse("1.00 k").unwrap(), 1000.0);

let mut fb = Formatter::new();
fb.with_scales(Scales::Binary());

assert_eq!(fb.try_parse("1.00 ki").unwrap(), 1024.0);

The parser accepts the micro sign µ as input.

Force a suffix in output

To force output to a certain suffix, use with_suffix. The value is scaled to match that suffix if possible.

use human_format::Formatter;

let mut f = Formatter::new();
f.with_suffix("M");

assert_eq!(f.format(100_000.0), "0.10 M");

If the suffix is not valid for the current Scales, the formatter falls back to automatic selection.

Micro sign output

Use with_micro_sign(true) to show µ for micro values in the output.

use human_format::Formatter;

let mut f = Formatter::new();
f.with_micro_sign(true);

assert_eq!(f.format(0.000001_f64), "1.00 µ");

Parsing accepts both u and µ.

Time scales

Scales::Time() uses a set of explicit unit multipliers for time. It uses average values where needed (for example, the average year is 365.2425 days). Use Scales::Time() when you want time-aware formatting and parsing.

use human_format::{Formatter, Scales};

let mut ft = Formatter::new();
ft.with_scales(Scales::Time());

// 90 seconds -> 1.50 m (minutes)
assert_eq!(ft.format(90.0), "1.50 m");
// Quarters (qtr) parse as three-month periods
assert!(ft.try_parse("1 qtr").is_ok());

For more examples please consult tests/demo.rs

Notes

• Months and years are approximate here. For precise calendar math, use a date-time library.
• Very large and very small numbers can lose precision when using f64.
• The with_suffix method uses the same suffix strings that try_parse accepts.

Suffix vs unit ambiguity

Some short tokens can be ambiguous. For example, the single letter m can mean milli (a magnitude suffix) or meter (a measurement unit) depending on how you configure the Formatter:

• Formatter::new().with_suffix("m") treats m as milli (scale).
• Formatter::new().with_units("m") appends m as the units string (meter).

To avoid ambiguity, prefer longer suffixes or specify units explicitly with with_units.

Case sensitivity

Suffix matching is case-sensitive: M (mega) is not the same as m (milli). If you want different aliases or case-insensitive parsing, add those aliases to the Scales you use.

parse_or_clamp behavior

The parse_or_clamp helper can be used when accepting user-provided suffixes that may be unknown or misspelled. Call it with clamp = true to interpret unknown suffixes as the largest available magnitude in the active Scales.

Important: when a Scales provides an explicit_map (for example Scales::Time()), parse_or_clamp will clamp to the largest multiplier defined in that explicit map rather than assuming a power-of-base value. This ensures consistent behavior for non-power-of-base scales such as time units (where the largest defined unit is Gyr).

Testing and correctness notes

We added a number of focused tests to ensure robust handling of edge-cases:

• Micro sign parsing and optional micro-sign output (tests/micro_sign.rs).
• Forced-suffix behavior including unknown-suffix fallbacks (tests/forced_suffix.rs).
• SI round-trip formatting for new prefixes R/Q and parsing validation (tests/si_roundtrip.rs).
• Time scale edge cases: months, quarters, parsing case-sensitivity, and clamp behavior (tests/time_edgecases.rs).

If you rely on case-insensitive parsing or custom aliases, construct a Scales with the aliases you need and pass it to Formatter::with_scales.

Contributing

Contributions are welcome.

When you add features, please include tests.

License

See the repository LICENSE file for license details.