143 lines
3.5 KiB
Markdown
143 lines
3.5 KiB
Markdown
# cpc
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calculation + conversion
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cpc parses and evaluates strings of math, with support for units and conversion. 128-bit decimal floating points are used for high accuracy.
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cpc lets you mix units, so for example `1 km - 1m` results in `Number { value: 999, unit: Meter }`.
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## Usage
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```rs
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use cpc::{eval, Unit::*}
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match eval("3m + 1cm", true, Celcius) {
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Ok(answer) => {
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// answer: Number { value: 301, unit: Unit::cm }
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println!("Evaluated value: {} {:?}", answer.value, answer.unit)
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},
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Err(e) => {
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println!(e)
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}
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}
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```
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## Examples
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```
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3 + 4 * 2
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8 % 3
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(4 + 1)km to light years
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10m/2s * 5s
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1 lightyear * 0.001mm in km2
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1m/s + 1mi/h in kilometers per h
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round(sqrt(2)^4)! liters
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10% of abs(sin(pi)) horsepower to watts
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```
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## Supported unit types
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- Normal numbers
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- Time
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- Length
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- Area
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- Volume
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- Mass
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- Digital storage (bytes etc)
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- Energy
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- Power
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- Pressure
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- Speed
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- Temperature
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## Accuracy
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cpc Uses 128-bit Decimal Floating Point (d128) numbers instead of Binary Coded Decimals for better accuracy. The result cpc gives will still not always be 100% accurate. I would recommend rounding the result to 20 decimals or less.
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## Performance
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In my case, I can expect `eval()` to take 100-200ms, and this scales pretty alright. However, putting numbers with a lot of digits into functions result in pretty poor performance. `log(e)` is one of the worst, and takes 500ms for me.
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## Errors
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cpc returns `Result`s with basic strings as errors. Just to be safe, you may want to handle panics (You can do that using `std::panic::catch_unwind`).
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# Dev Instructions
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## Get started
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Install [Rust](https://www.rust-lang.org). This project was built in Rust 1.40.
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## Commands
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Run cpc with a CLI argument as input:
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```
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cargo run -- '100ms to s'
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```
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Run with debugging, which shows some extra logs:
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```
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cargo run -- '100ms to s' --debug
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```
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Run tests:
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```
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cargo test
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```
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## Adding a unit
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### 1. Add the unit
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In `src/units.rs`, units are specified like this:
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```rs
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pub enum UnitType {
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Time,
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// etc
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}
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// ...
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create_units!(
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Nanosecond: (Time, d128!(1)),
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Microsecond: (Time, d128!(1000)),
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// etc
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)
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```
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The number associated with a unit is it's "weight". For example, if a second's weight is `1`, then a minute's weight is `1000`.
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I have found [translatorscafe.com](https://www.translatorscafe.com/unit-converter) and [calculateme.com](https://www.calculateme.com/) to be good websites for unit convertion. Wikipedia is worth looking at as well.
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### 2. Add a test for the unit
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Make sure to also add a test for each unit. The tests look like this:
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```rs
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assert_eq!(convert_test(1000.0, Meter, Kilometer), 1.0);
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```
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Basically, 1000 Meter == 1 Kilometer.
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### 3. Add the unit to the lexer
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Text is turned into tokens (some of which are units) in `lexer.rs`. Here's one example:
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```rs
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// ...
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match string {
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"h" | "hr" | "hrs" | "hour" | "hours" => tokens.push(Token::Unit(Hour)),
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// etc
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}
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// ...
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```
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## Potential Improvements
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### General
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- Support for math in `6'4"` syntax, like `3'+2'4"`. Currently needs to be written like `3'+3'+4"`
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- The functions in units.rs have a lot of manual if statements. This could probably be replaced with a pretty advanced macro.
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- Support for lexing words, like `one billion`
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### Potential unit types
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Nice list of units: https://support.google.com/websearch/answer/3284611
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- Currency: How would you go about dynamically updating the weights?
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- Fuel consumption
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- Data transfer rate
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- Color codes
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- Force
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- Roman numerals
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- Angles
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- Electric current, capacitance, charge, conductance, volts
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- Flow rate
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- Frequency
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