# `si-scale`
[](https://crates.io/crates/si-scale)
[](https://docs.rs/si-scale)
[](https://rust-lang.github.io/rfcs/2495-min-rust-version.html)
[](https://github.com/u0xy/si-scale/actions)
Format value with units according to SI ([système international d’unités](https://en.wikipedia.org/wiki/International_System_of_Units)).
_Version requirement: rustc 1.50+_
```toml
[dependencies]
si-scale = "0.1"
```
## Getting started
This crate parses and 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 is essentially
agnostic of units per-se; you can totally keep representing units with
strings or [uom](https://crates.io/crates/uom), or something else.
### Pre-defined helper functions
You can use one of the predefined helper functions to format numbers:
```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);
```
Currently the helper functions are:
| `number_()` | `"{}"` | `UnitOnly` | B1000 | `_` | `1.234567`, `16` |
| --- | -- | --- | --- | --- | --- |
| `seconds()` | `"{}"` | `UnitAndBelow` | B1000 | none | `1.234567 µs`, `16 ms` |
| `seconds3()` | `"{:.3}"` | `UnitAndBelow` | B1000 | none | `1.235 µs`, `16.000 ms`|
| --- | -- | --- | --- | --- | --- |
| `bytes()` | `"{}"` | `UnitAndAbove` | B1000 | `_` | `1.234_567 kB` |
| `bytes_()` | `"{}"` | `UnitOnly` | B1000 | `_` | `1_234_567 B` |
| `bytes1()` | `"{:.1}"` | `UnitAndAbove` | B1000 | none | `2.3 TB` |
| --- | -- | --- | --- | --- | --- |
| `bibytes()` | `"{}"` | `UnitAndAbove` | B1024 | `_` | `1.234_567 MiB` |
| `bibytes1()` | `"{:.1}"` | `UnitAndAbove` | B1024 | none | `1.2 GiB` |
- The prefix constraint reduces the possible scales for a value (it is
"unit" like in 1, not like in units of measurements). For instance,
`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. The
`UnitAndBelow` constraint means the provided value won't use upper scales
such as kilo, Mega, Tera, etc, but a small value will be scaled: 16 µs
could be displayed, but not 16 Gs.
- Base B1000 means 1k = 1000, the base B1024 means 1k = 1024
- 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.
- The mantissa format string only acts on the mantissa: `"{}"` will
display the value with all its digits or no digits if it is round, and
`"{:.1}"` for instance will always display one decimal.
## Custom helper functions
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.
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");
}
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
With base = 1000, 1k = 1000, 1M = 1\_000\_000, 1m = 0.001, 1µ = 0.000\_001,
etc.
| .. | .. | -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.
## 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.
```rust
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.
```rust
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.
```rust
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.
```rust
use si_scale::format_value;
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.