si_scale/

lib.rs

#![warn(missing_docs)]
#![allow(clippy::needless_doctest_main)]

//! Format value with units according to SI ([système international d'unités](https://en.wikipedia.org/wiki/International_System_of_Units)).
//!
//! Version requirement: _rustc 1.74+_
//!
//! ```toml
//! [dependencies]
//! si-scale = "0.2"
//! ```
//!
//! ## Overview
//!
//! This crate formats numbers using the
//! [SI Scales](https://en.wikipedia.org/wiki/International_System_of_Units):
//! from 1 y (yocto, i.e. 1e-24) to 1 Y (Yotta, i.e. 1e24).
//!
//! It has the same purpose as the great
//! [human-repr](https://docs.rs/human-repr), but strikes a different balance:
//!
//! - this crate yields more terse code at the call sites
//! - it gives you more control over the output. As shown later in this page,
//!   you can extend it pretty easily to handle throughput, etc. (seriously, see
//!   below)
//! - but it only operates on numbers, so it does not prevent you from using a
//!   function to print meters on a duration value (which human-repr does
//!   brilliantly).
//!
//! ## Getting started
//!
//! To use this crate, either use one of the few pre-defined helper functions,
//! or build your own.
//!
//! Basic example:
//!
//! ```rust
//! use si_scale::helpers::{seconds, seconds3};
//!
//! let actual = format!("{}", seconds(1.3e-5));
//! let expected = "13 µs";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("{}", seconds3(1.3e-5));
//! let expected = "13.000 µs";
//! assert_eq!(actual, expected);
//! ```
//!
//! ## Pre-defined helper functions
//!
//! The helper functions use the following naming convention:
//!
//! - the name indicates the units to use
//! - a number suffix indicates the decimal digits for floating points
//! - a `_` suffix indicates the digits use "thousands grouping"
//!
//! But that's up to you to depart from that when writing your own functions.
//!
//! Currently the helper functions are:
//!
//! | helper fn    | input                  | output                 |
//! | ---          | ---                    | ---                    |
//! | `number_()`  | `1.234567`, `1515`     | `1.234_567`, `1_515`   |
//! | ---          | ---                    | ---                    |
//! | `seconds()`  | `1.234567e-6`, `16e-3` | `1.234567 µs`, `16 ms` |
//! | `seconds3()` | `1.234567e-6`, `16e-3` | `1.235 µs`, `16.000 ms`|
//! | ---          | ---                    | ---                    |
//! | `bytes()`    | `1234567`              | `1.234567 MB`          |
//! | `bytes_()`   | `1234567`              | `1_234_567 B`          |
//! | `bytes1()`   | `2.3 * 1e12`           | `2.3 TB`               |
//! | `bytes2()`   | `2.3 * 1e12`           | `2.30 TB`              |
//! | ---          | ---                    | ---                    |
//! | `bibytes()`  | `1024 * 1024 * 1.25`   | `1.25 MiB`             |
//! | `bibytes1()` | `1024 * 1024 * 1.25`   | `1.3 MiB`              |
//! | `bibytes2()` | `1024 * 1024 * 1.25`   | `1.25 MiB`             |
//!
//! ## Custom helper functions - BYOU (bring your own unit)
//!
//! To define your own format function, use the
//! [`scale_fn!()`](`crate::scale_fn!()`) macro. All pre-defined helper
//! functions from this crate are defined using this macro.
//!
//! | helper fn    | mantissa  | prefix constraint | base  | groupings | input                  | output                 |
//! | ---          | --        | ---               | ---   | ---       | ---                    | ---                    |
//! | `number_()`  | `"{}"`    | `UnitOnly`        | B1000 | `_`       | `1.234567`, `1515`     | `1.234_567`, `1_515`   |
//! | ---          | --        | ---               | ---   | ---       | ---                    | ---                    |
//! | `seconds()`  | `"{}"`    | `UnitAndBelow`    | B1000 | none      | `1.234567e-6`, `16e-3` | `1.234567 µs`, `16 ms` |
//! | `seconds3()` | `"{:.3}"` | `UnitAndBelow`    | B1000 | none      | `1.234567e-6`, `16e-3` | `1.235 µs`, `16.000 ms`|
//! | ---          | --        | ---               | ---   | ---       | ---                    | ---                    |
//! | `bytes()`    | `"{}"`    | `UnitAndAbove`    | B1000 | none      | `1234567`              | `1.234567 MB`          |
//! | `bytes_()`   | `"{}"`    | `UnitOnly`        | B1000 | `_`       | `1234567`              | `1_234_567 B`          |
//! | `bytes1()`   | `"{:.1}"` | `UnitAndAbove`    | B1000 | none      | `2.3 * 1e12`           | `2.3 TB`               |
//! | `bytes2()`   | `"{:.2}"` | `UnitAndAbove`    | B1000 | none      | `2.3 * 1e12`           | `2.30 TB`              |
//! | ---          | --        | ---               | ---   | ---       | ---                    | ---                    |
//! | `bibytes()`  | `"{}"`    | `UnitAndAbove`    | B1024 | none      | `1024 * 1024 * 1.25`   | `1.25 MiB`             |
//! | `bibytes1()` | `"{:.1}"` | `UnitAndAbove`    | B1024 | none      | `1024 * 1024 * 1.25`   | `1.3 MiB`              |
//! | `bibytes2()` | `"{:.2}"` | `UnitAndAbove`    | B1024 | none      | `1024 * 1024 * 1.25`   | `1.25 MiB`             |
//!
//! The additional table columns show the underlying controls.
//!
//! ### The "mantissa" column
//!
//! It is a format string which only acts on the mantissa after scaling. For
//! instance, `"{}"` will display the value with all its digits or no digits if
//! it is round, and `"{:.1}"` for instance will always display one decimal.
//!
//! ### The "prefix constraint" column
//!
//! In a nutshell, this allows values to be represented in unsurprising scales:
//! for instance, you would never write `1.2 ksec`, but always `1200 sec` or
//! `1.2e3 sec`. In the same vein, you would never write `2 mB`, but always
//! `0.002 B` or `2e-3 B`.
//!
//! So, here the term "unit" refers to the unit scale (`1`), and has nothing to
//! do with units of measurements. It constrains the possible scales for a
//! value:
//!
//! - `UnitOnly` means the provided value won't be scaled: if you provide a
//!   value larger than 1000, say 1234, it will be printed as 1234.
//! - `UnitAndAbove` means the provided value can only use higher scales, for
//!   instance `16 GB` but never `4.3 µB`.
//! - `UnitAndBelow` means the provided value can only use lower scales, for
//!   instance `1.3 µsec` but not `16 Gsec`.
//!
//! ### The "base" column
//!
//! Base B1000 means 1k = 1000, the base B1024 means 1k = 1024. This is defined
//! in an [IEC document](https://www.iec.ch/prefixes-binary-multiples). If you
//! set the base to `B1024`, the mantissa will be scaled appropriately, but in
//! most cases, you will be using `B1000`.
//!
//! ### The "groupings" column
//!
//! Groupings refer to "thousands groupings"; the provided char will be
//! used (for instance 1234 is displayed as 1\_234), if none, the value is
//! displayed 1234.
//!
//! ### Example - how to define a helper for kibits/s
//!
//! For instance, let's define a formatting function for bits per sec which
//! prints the mantissa with 2 decimals, and also uses base 1024 (where 1 ki =
//! 1024). Note that although we define the function in a separate module,
//! this is not a requirement.
//!
//! ```rust
//! mod unit_fmt {
//!     use si_scale::scale_fn;
//!     use si_scale::prelude::Value;
//!
//!     // defines the `bits_per_sec()` function
//!     scale_fn!(bits_per_sec,
//!               base: B1024,
//!               constraint: UnitAndAbove,
//!               mantissa_fmt: "{:.2}",
//!               groupings: '_',
//!               unit: "bit/s",
//!               doc: "Return a string with the value and its si-scaled unit of bit/s.");
//! }
//!
//! use unit_fmt::bits_per_sec;
//!
//! fn main() {
//!     let x = 2.1 * 1024 as f32;
//!     let actual = format!("throughput: {:>15}", bits_per_sec(x));
//!     let expected = "throughput:    2.10 kibit/s";
//!     assert_eq!(actual, expected);
//!
//!     let x = 2;
//!     let actual = format!("throughput: {}", bits_per_sec(x));
//!     let expected = "throughput: 2.00 bit/s";
//!     assert_eq!(actual, expected);
//! }
//!
//! ```
//!
//! You can omit the `groupings` argument of the macro to not separate
//! thousands.
//!
//! ## SI Scales - Developer doc
//!
//! With base = 1000, 1k = 1000, 1M = 1\_000\_000, 1m = 0.001, 1µ = 0.000\_001,
//! etc.
//!
//! | min (incl.) | max (excl.)      | magnitude | prefix          |
//! | ---         | ---              | ---       | ----            |
//! | ..          | ..               | -24       | `Prefix::Yocto` |
//! | ..          | ..               | -21       | `Prefix::Zepto` |
//! | ..          | ..               | -18       | `Prefix::Atto`  |
//! | ..          | ..               | -15       | `Prefix::Femto` |
//! | ..          | ..               | -12       | `Prefix::Pico`  |
//! | ..          | ..               | -9        | `Prefix::Nano`  |
//! | 0.000\_001  | 0.001            | -6        | `Prefix::Micro` |
//! | 0.001       | 1                | -3        | `Prefix::Milli` |
//! | 1           | 1_000            | 0         | `Prefix::Unit`  |
//! | 1000        | 1\_000\_000      | 3         | `Prefix::Kilo`  |
//! | 1\_000\_000 | 1\_000\_000\_000 | 6         | `Prefix::Mega`  |
//! | ..          | ..               | 9         | `Prefix::Giga`  |
//! | ..          | ..               | 12        | `Prefix::Tera`  |
//! | ..          | ..               | 15        | `Prefix::Peta`  |
//! | ..          | ..               | 18        | `Prefix::Exa`   |
//! | ..          | ..               | 21        | `Prefix::Zetta` |
//! | ..          | ..               | 24        | `Prefix::Yotta` |
//!
//! The base is usually 1000, but can also be 1024 (bibytes).
//!
//! With base = 1024, 1ki = 1024, 1Mi = 1024 * 1024, etc.
//!
//! ### API overview
//!
//! The central representation is the [`Value`](`crate::value::Value`) type,
//! which holds
//!
//! - the mantissa,
//! - the SI unit prefix (such as "kilo", "Mega", etc),
//! - and the base which represents the cases where "1 k" means 1000 (most
//!   common) and the cases where "1 k" means 1024 (for kiB, MiB, etc).
//!
//! This crate provides 2 APIs: a low-level API, and a high-level API for
//! convenience.
//!
//! For the low-level API, the typical use case is
//!
//! - first parse a number into a [`Value`](`crate::value::Value`). For doing
//!   this, you have to specify the base, and maybe some constraint on the SI
//!   scales. See [`Value::new()`](`crate::value::Value::new()`) and
//!   [`Value::new_with()`](`crate::value::Value::new_with()`)
//!
//! - then display the `Value` either by yourself formatting the mantissa
//!   and prefix (implements the `fmt::Display` trait), or using the provided
//!   Formatter.
//!
//! For the high-level API, the typical use cases are
//!
//! 1. parse and display a number using the provided functions such as
//!    `bibytes()`, `bytes()` or `seconds()`, they will choose for each number
//!    the most appropriate SI scale.
//!
//! 2. In case you want the same control granularity as the low-level API
//!    (e.g. constraining the scale in some way, using some base, specific
//!    mantissa formatting), then you can build a custom function using the
//!    provided macro `scale_fn!()`. The existing functions such as
//!    `bibytes()`, `bytes()`, `seconds()` are all built using this same
//!    macro.
//!
//! ### The high-level API
//!
//! The `seconds3()` function parses a number into a `Value` and displays it
//! using 3 decimals and the appropriate scale for seconds (`UnitAndBelow`),
//! so that non-sensical scales such as kilo-seconds can't be output. The
//! `seconds()` function does the same but formats the mantissa with the
//! default `"{}"`, so no decimals are printed for integer mantissa.
//!
//! ```
//! use si_scale::helpers::{seconds, seconds3};
//!
//! let actual = format!("result is {:>15}", seconds(1234.5678));
//! let expected = "result is     1234.5678 s";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {:>10}", seconds3(12.3e-7));
//! let expected = "result is   1.230 µs";
//! assert_eq!(actual, expected);
//! ```
//!
//! The `bytes()` function parses a number into a `Value` _using base 1000_
//! and displays it using 1 decimal and the appropriate scale for bytes
//! (`UnitAndAbove`), so that non-sensical scales such as milli-bytes may not
//! appear.
//!
//! ```
//! use si_scale::helpers::{bytes, bytes1};
//!
//! let actual = format!("result is {}", bytes1(12_345_678));
//! let expected = "result is 12.3 MB";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {:>10}", bytes(16));
//! let expected = "result is       16 B";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {}", bytes(0.12));
//! let expected = "result is 0.12 B";
//! assert_eq!(actual, expected);
//! ```
//!
//! The `bibytes1()` function parses a number into a `Value` _using base 1024_
//! and displays it using 1 decimal and the appropriate scale for bytes
//! (`UnitAndAbove`), so that non-sensical scales such as milli-bytes may not
//! appear.
//!
//! ```
//! use si_scale::helpers::{bibytes, bibytes1};
//!
//! let actual = format!("result is {}", bibytes1(12_345_678));
//! let expected = "result is 11.8 MiB";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {}", bibytes(16 * 1024));
//! let expected = "result is 16 kiB";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {:>10}", bibytes1(16));
//! let expected = "result is     16.0 B";
//! assert_eq!(actual, expected);
//!
//! let actual = format!("result is {}", bibytes(0.12));
//! let expected = "result is 0.12 B";
//! assert_eq!(actual, expected);
//! ```
//!
//! ### The low-level API
//!
//! #### Creating a `Value` with `Value::new()`
//!
//! The low-level function [`Value::new()`](`crate::value::Value::new()`)
//! converts any number convertible to f64 into a `Value` using base 1000. The
//! `Value` struct implements `From` for common numbers and delegates to
//! `Value::new()`, so they are equivalent in practice. Here are a few
//! examples.
//!
//! ```rust
//! use std::convert::From;
//! use si_scale::prelude::*;
//!
//! let actual = Value::from(0.123);
//! let expected = Value {
//!     mantissa: 123f64,
//!     prefix: Prefix::Milli,
//!     base: Base::B1000,
//! };
//! assert_eq!(actual, expected);
//! assert_eq!(Value::new(0.123), expected);
//!
//! let actual: Value = 0.123.into();
//! assert_eq!(actual, expected);
//!
//! let actual: Value = 1300i32.into();
//! let expected = Value {
//!     mantissa: 1.3f64,
//!     prefix: Prefix::Kilo,
//!     base: Base::B1000,
//! };
//! assert_eq!(actual, expected);
//!
//! let actual: Vec<Value> = vec![0.123f64, -1.5e28]
//!     .iter().map(|n| n.into()).collect();
//! let expected = vec![
//!     Value {
//!         mantissa: 123f64,
//!         prefix: Prefix::Milli,
//!         base: Base::B1000,
//!     },
//!     Value {
//!         mantissa: -1.5e4f64,
//!         prefix: Prefix::Yotta,
//!         base: Base::B1000,
//!     },
//! ];
//! assert_eq!(actual, expected);
//! ```
//!
//! As you can see in the last example, values which scale are outside of the
//! SI prefixes are represented using the closest SI prefix.
//!
//! #### Creating a `Value` with `Value::new_with()`
//!
//! The low-level [`Value::new_with()`](`crate::value::Value::new_with()`)
//! operates similarly to [`Value::new()`](`crate::value::Value::new()`) but
//! also expects a base and a constraint on the scales you want to use. In
//! comparison with the simple `Value::new()`, this allows base 1024 scaling
//! (for kiB, MiB, etc) and preventing upper scales for seconds or lower
//! scales for integral units such as bytes (e.g. avoid writing 1300 sec as
//! 1.3 ks or 0.415 B as 415 mB).
//!
//! ```rust
//! use si_scale::prelude::*;
//!
//! // Assume this is seconds, no kilo-seconds make sense.
//! let actual = Value::new_with(1234, Base::B1000, Constraint::UnitAndBelow);
//! let expected = Value {
//!     mantissa: 1234f64,
//!     prefix: Prefix::Unit,
//!     base: Base::B1000,
//! };
//! assert_eq!(actual, expected);
//! ```
//!
//! Don't worry yet about the verbosity, the following parser helps with this.
//!
//! #### Formatting values
//!
//! In this example, the number `x` is converted into a value and displayed
//! using the most appropriate SI prefix. The user chose to constrain the
//! prefix to be anything lower than `Unit` (1) because kilo-seconds make
//! no sense.
//!
//! ```
//! use si_scale::format_value;
//! # fn main() {
//! use si_scale::{value::Value, base::Base, prefix::Constraint};
//!
//! let x = 1234.5678;
//! let v = Value::new_with(x, Base::B1000, Constraint::UnitAndBelow);
//! let unit = "s";
//!
//! let actual = format!(
//!     "result is {}{u}",
//!     format_value!(v, "{:.5}", groupings: '_'),
//!     u = unit
//! );
//! let expected = "result is 1_234.567_80 s";
//! assert_eq!(actual, expected);
//! # }
//! ```
//!
//! ## Run code-coverage
//!
//! Install the llvm-tools-preview component and grcov
//!
//! ```sh
//! rustup component add llvm-tools-preview
//! cargo install grcov
//! ```
//!
//! Install nightly
//!
//! ```sh
//! rustup toolchain install nightly
//! ```
//!
//! The following make invocation will switch to nigthly run the tests using
//! Cargo, and output coverage HTML report in `./coverage/`
//!
//! ```sh
//! make coverage
//! ```
//!
//! The coverage report is located in `./coverage/index.html`
//!
//! ## License
//!
//! Licensed under either of
//!
//! - [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
//! - [MIT license](http://opensource.org/licenses/MIT)
//!
//! at your option.
//!
//! ### Contribution
//!
//! Unless you explicitly state otherwise, any contribution intentionally submitted
//! for inclusion in the work by you, as defined in the Apache-2.0 license, shall
//! be dual licensed as above, without any additional terms or conditions.

/// Error type used by this crate.
#[derive(Debug, PartialEq, Eq)]
pub enum SIUnitsError {
    /// Indicates an error occurred when parsing the exponent.
    ExponentParsing(String),
}

/// Result type used by this crate.
pub type Result<T> = std::result::Result<T, SIUnitsError>;

pub mod base;
pub mod format;
pub mod helpers;
pub mod prefix;
pub mod value;

/// Holds first-class citizens of this crate, for convenience.
pub mod prelude {
    pub use crate::base::Base;
    pub use crate::prefix::{Constraint, Prefix};
    pub use crate::value::Value;
}