Crate signifix [−] [src]

Number Formatter of Fixed Significance with Metric or Binary Prefix

Formats a given number in one of the three Signifix notations as defined below by determining

  1. the appropriate metric or binary prefix and
  2. the decimal mark position in such a way as to sustain a fixed number of four significant figures.

Signifix Notations

Three notations are defined,

With Metric Prefix

The two Signifix notations with metric prefix comprise

  • a signed significand of four significant figures normalized from ±1.000 to ±999.9 to cover the three powers of ten of a particular metric prefix with the three different decimal mark positions between these four figures, and
  • a metric prefix symbol or its placeholder in case of no prefix
    • either being appended along with a whitespace as in ±1.234␣k, that is the default notation,
    • or replacing the decimal mark of the significand as in ±1k234, that is the alternate notation.

In default notation the placeholder is another whitespace as in ±1.234␣␣ to align consistently, while in alternate notation it is a number sign as in ±1#234 to conspicuously separate the integer from the fractional part of the significand.

The plus sign of positive numbers is optional.

With Binary Prefix

The one Signifix notation with binary prefix comprises

  • a signed significand of four significant figures normalized from ±1.000 over ±999.9 to ±1 023 to cover the four powers of ten of a particular binary prefix with the three different decimal mark positions between these four figures and a thousands separator, and
  • a binary prefix symbol or its placeholder in case of no prefix being appended along with a whitespace as in ±1.234␣Ki.

To align consistently, the placeholder is another two whitespaces as in ±1.234␣␣␣ while the thousands separator is a whitespace as in ±1␣023␣Ki.

The plus sign of positive numbers is optional.

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 = "0.5.0"

and this to your crate root:

#![feature(try_from)] // Until stabilized. Requires nightly Rust.

extern crate signifix;

Examples

The Signifix notations result in a fixed number of characters preventing jumps to the left or right:

use std::convert::TryFrom; // Until stabilized.

use signifix::{metric, binary, Result};

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

// Three different decimal mark positions covering the three powers of ten
// of a particular metric prefix.
assert_eq!(metric(1E-04), Ok(("100.0 µ".into(), "100µ0".into()))); // 3rd
assert_eq!(metric(1E-03), Ok(("1.000 m".into(), "1m000".into()))); // 1st
assert_eq!(metric(1E-02), Ok(("10.00 m".into(), "10m00".into()))); // 2nd
assert_eq!(metric(1E-01), Ok(("100.0 m".into(), "100m0".into()))); // 3rd
assert_eq!(metric(1E+00), Ok(("1.000  ".into(), "1#000".into()))); // 1st
assert_eq!(metric(1E+01), Ok(("10.00  ".into(), "10#00".into()))); // 2nd
assert_eq!(metric(1E+02), Ok(("100.0  ".into(), "100#0".into()))); // 3rd
assert_eq!(metric(1E+03), Ok(("1.000 k".into(), "1k000".into()))); // 1st
assert_eq!(metric(1E+04), Ok(("10.00 k".into(), "10k00".into()))); // 2nd
assert_eq!(metric(1E+05), Ok(("100.0 k".into(), "100k0".into()))); // 3rd
assert_eq!(metric(1E+06), Ok(("1.000 M".into(), "1M000".into()))); // 1st

// Three different decimal mark positions and a thousands separator covering
// the four powers of ten of a particular binary prefix.
assert_eq!(binary(1_024f64.powi(0) * 1E+00), Ok("1.000   ".into())); // 1st
assert_eq!(binary(1_024f64.powi(0) * 1E+01), Ok("10.00   ".into())); // 2nd
assert_eq!(binary(1_024f64.powi(0) * 1E+02), Ok("100.0   ".into())); // 3rd
assert_eq!(binary(1_024f64.powi(0) * 1E+03), Ok("1 000   ".into())); // 4th
assert_eq!(binary(1_024f64.powi(1) * 1E+00), Ok("1.000 Ki".into())); // 1st
assert_eq!(binary(1_024f64.powi(1) * 1E+01), Ok("10.00 Ki".into())); // 2nd
assert_eq!(binary(1_024f64.powi(1) * 1E+02), Ok("100.0 Ki".into())); // 3rd
assert_eq!(binary(1_024f64.powi(1) * 1E+03), Ok("1 000 Ki".into())); // 4th
assert_eq!(binary(1_024f64.powi(2) * 1E+00), Ok("1.000 Mi".into())); // 1st

// Rounding over prefixes is safe against floating-point inaccuracies.
assert_eq!(metric(999.949_999_999_999_8),
    Ok(("999.9  ".into(), "999#9".into())));
assert_eq!(metric(999.949_999_999_999_9),
    Ok(("1.000 k".into(), "1k000".into())));
assert_eq!(binary(1_023.499_999_999_999_94),
    Ok("1 023   ".into()));
assert_eq!(binary(1_023.499_999_999_999_95),
    Ok("1.000 Ki".into()));

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

#![feature(i128_type)] // Until stabilized.

use std::convert::TryFrom; // Until stabilized.

use std::f64;
use signifix::metric::{Signifix, Error, DEF_MIN_LEN};

let format_rate = |bytes: u128, nanoseconds: u128| -> String {
    let bytes_per_second = bytes as f64 / nanoseconds as f64 * 1E+09;
    let unit = "B/s";
    let rate = match Signifix::try_from(bytes_per_second) {
        Ok(rate) => if rate.factor() < 1E+00 {
            " - slow - ".into() // instead of mB/s, µB/s, ...
        } else {
            format!("{}{}", rate, unit) // normal rate
        },
        Err(case) => match case {
            Error::OutOfLowerBound(rate) => if rate == 0f64 {
                " - idle - " // no progress at all
            } else {
                " - slow - " // almost no progress
            },
            Error::OutOfUpperBound(rate) => if rate == f64::INFINITY {
                " - ---- - " // zero nanoseconds
            } else {
                " - fast - " // awkwardly fast
            },
            Error::Nan => " - ---- - ", // zero bytes in zero nanoseconds
        }.into(),
    };
    assert_eq!(rate.chars().count(), DEF_MIN_LEN + unit.chars().count());
    rate
};

assert_eq!(format_rate(42_667, 300_000_000_000), "142.2  B/s");
assert_eq!(format_rate(42_667, 030_000_000_000), "1.422 kB/s");
assert_eq!(format_rate(42_667, 003_000_000_000), "14.22 kB/s");
assert_eq!(format_rate(00_001, 003_000_000_000), " - slow - ");
assert_eq!(format_rate(00_000, 003_000_000_000), " - idle - ");
assert_eq!(format_rate(42_667, 000_000_000_000), " - ---- - ");

Or to monitor a measured quantity like an electrical current including its direction with positive numbers being padded to align with negative ones:

use std::convert::TryFrom; // Until stabilized.

use signifix::metric::{Signifix, Result, DEF_MAX_LEN};

let format_load = |amps| -> Result<String> {
    if let Some(amps) = amps {
        Signifix::try_from(amps)
            .map(|amps| format!("{:>1$}A", amps, DEF_MAX_LEN))
    } else {
        Ok("     0  A".into())
    }
};

assert_eq!(format_load(Some( 1.476E-06)), Ok(" 1.476 µA".into()));
assert_eq!(format_load(None),             Ok("     0  A".into()));
assert_eq!(format_load(Some(-2.927E-06)), Ok("-2.927 µA".into()));

While to visualize a change in file size, a plus sign might be preferred for positive numbers:

use std::convert::TryFrom; // Until stabilized.

use signifix::metric::{Signifix, Error, Result};

let format_diff = |curr, prev| -> Result<String> {
    Signifix::try_from(curr - prev).map(|diff| format!("{:+#}", diff))
        .or_else(|case| if case == Error::OutOfLowerBound(0f64)
            { Ok("=const".into()) } else { Err(case) })
};

assert_eq!(format_diff(78_346, 57_393), Ok("+20k95".into()));
assert_eq!(format_diff(93_837, 93_837), Ok("=const".into()));
assert_eq!(format_diff(27_473, 36_839), Ok("-9k366".into()));

The binary prefix instead suits well to visualize quantities being multiples of powers of two, such as memory boundaries due to binary addressing:

use std::convert::TryFrom; // Until stabilized.

use signifix::binary::{Signifix, Error, Result};

let format_used = |used: usize, size: usize| -> Result<String> {
    if used == 0 {
        let size = Signifix::try_from(size)?;
        return Ok(format!("    0   B (    0 %) of {}B)", size));
    }
    let p100 = Signifix::try_from(used as f64 / size as f64 * 100.0)
        .map(|p100| format!("{:.*} %", p100.exponent(), p100.significand()))
        .or_else(|error| if let Error::OutOfLowerBound(_) = error
            { Ok("  < 1 %".into()) } else { Err(error) })?;
    let used = Signifix::try_from(used)?;
    let size = Signifix::try_from(size)?;
    Ok(format!("{}B ({}) of {}B)", used, p100, size))
};

assert_eq!(format_used(0_000usize.pow(1), 1_024usize.pow(3)),
    Ok("    0   B (    0 %) of 1.000 GiB)".into()));
assert_eq!(format_used(1_024usize.pow(2), 1_024usize.pow(3)),
    Ok("1.000 MiB (  < 1 %) of 1.000 GiB)".into()));
assert_eq!(format_used(3_292usize.pow(2), 1_024usize.pow(3)),
    Ok("10.34 MiB (1.009 %) of 1.000 GiB)".into()));
assert_eq!(format_used(8_192usize.pow(2), 1_024usize.pow(3)),
    Ok("64.00 MiB (6.250 %) of 1.000 GiB)".into()));
assert_eq!(format_used(1_000usize.pow(3), 1_024usize.pow(3)),
    Ok("953.7 MiB (93.13 %) of 1.000 GiB)".into()));
assert_eq!(format_used(1_024usize.pow(3), 1_024usize.pow(3)),
    Ok("1.000 GiB (100.0 %) of 1.000 GiB)".into()));

Modules

binary

Formatter of Signifix default notation with binary prefix.
metric

Formatter of Signifix default and alternate notation with metric prefix.

Enums

Error

A common error arising from this crate's modules.

Type Definitions

Result

The canonical Result type using this crate's Error type.