Number Formatter of Fixed Significance with Metric Unit Prefix

Signifix guarantees a fixed number of significant figures and a fixed number of resulting characters by automatically choosing the metric unit prefix and appropriately adjusting the decimal point position.

Usage

This crate is on crates.io and can be used by adding signifix to the dependencies in your project's Cargo.toml:

[dependencies]
signifix = "0.3.0"

and this to your crate root:

# #![allow(unused_attributes)]
#![feature(try_from)] // Until stabilized.

extern crate signifix;

Examples

The fixed number of significant figures and resulting characters prevent the digits and prefixed units from jumping to the left or right:

# #![feature(try_from)]
use std::convert::TryFrom; // Until stabilized.

use signifix::{Signifix, Result};

let format = |number| -> Result<String> {
	Ok(format!("{}", Signifix::try_from(number)?))
};

assert_eq!(format(1e-04).ok(), Some("100.0 µ".into()));
assert_eq!(format(1e-03).ok(), Some("1.000 m".into()));
assert_eq!(format(1e-02).ok(), Some("10.00 m".into()));
assert_eq!(format(1e-01).ok(), Some("100.0 m".into()));
assert_eq!(format(1e+00).ok(), Some("1.000  ".into()));
assert_eq!(format(1e+01).ok(), Some("10.00  ".into()));
assert_eq!(format(1e+02).ok(), Some("100.0  ".into()));
assert_eq!(format(1e+03).ok(), Some("1.000 k".into()));
assert_eq!(format(1e+04).ok(), Some("10.00 k".into()));
assert_eq!(format(1e+05).ok(), Some("100.0 k".into()));
assert_eq!(format(1e+06).ok(), Some("1.000 M".into()));

This is useful to smoothly refresh a transfer rate inside a terminal:

# #![feature(try_from)]
use std::convert::TryFrom; // Until stabilized.

use signifix::{Signifix, Result};

let format_rate = |bytes, seconds| -> Result<String> {
	Ok(format!("{}B/s", Signifix::try_from(bytes as f64 / seconds as f64)?))
};

assert_eq!(format_rate(42_667, 300).ok(), Some("142.2  B/s".into()));
assert_eq!(format_rate(42_667, 030).ok(), Some("1.422 kB/s".into()));
assert_eq!(format_rate(42_667, 003).ok(), Some("14.22 kB/s".into()));

Or to monitor a measured quantity like an electrical current including its direction with an optional space placeholder to align with negative values.

# #![feature(try_from)]
use std::convert::TryFrom; // Until stabilized.

use signifix::{Signifix, Result};

let format_load = |current| -> Result<String> {
	Ok(format!("{:#}A", Signifix::try_from(current)?))
};

assert_eq!(format_load( 1.476e-06).ok(), Some(" 1.476 µA".into()));
assert_eq!(format_load(-2.927e-06).ok(), Some("-2.927 µA".into()));

In case of displaying a file size difference after modification, a plus sign might be preferred for positive values:

# #![feature(try_from)]
use std::convert::TryFrom; // Until stabilized.

use signifix::{Signifix, Result};

let format_diff = |curr, prev| -> Result<String> {
	Ok(format!("{:+}B", Signifix::try_from(curr - prev)?))
};

assert_eq!(format_diff(78_346, 57_393).ok(), Some("+20.95 kB".into()));
assert_eq!(format_diff(27_473, 46_839).ok(), Some("-19.37 kB".into()));