🗿 fixed-point

Fixed point arithmetic with BigInt. Minimalistic library that can be used for money or scientific calculations with known precision.

$3

Install package npm install fixed-point or include minified script on page.

``js
import { FixedPoint } from 'fixed-point';

// Simple example: 0.3 - 0.2 = 0.1
console.log(new FixedPoint(0.3).sub(0.2).toString());

// Price with 30% discount, rounding benefiting the customer
FixedPoint.setRounding('floor');
console.log(new FixedPoint('99.95').mul(0.70).toFixed())

// Bitcoin fee with banker rounding: 1.0 BTC - 0.00005 BTC = 0.99995000 BTC
FixedPoint.setRounding('even');
FixedPoint.setPrecision(8);
console.log(new FixedPoint('1').sub('0.00005').toFixed() + ' BTC');

// Rounding mode for fast calculations
FixedPoint.setRounding('trunc');
FixedPoint.setPrecision(15);
console.log(new FixedPoint('3.14159265358979').mul('2'));
`

$3

* new FixedPoint(string) - constructor from String
* new FixedPoint(number) - constructor from Number
* a.toString() - conversion to String
* a.toFixed() - conversion to String
* FixedPoint.setPrecision(number) - set precision (2 decimal places is default)
* FixedPoint.setRounding(string) - set rounding ('trunc'|'floor'|'ceil'|'even'), 'even' is default
* a.add(b) - addition (exact)
* a.sub(b) - subtraction (exact)
* a.mul(b) - multiplication (rounded)
* a.div(b) - division (rounded)
* a.eq(b) - a == b
* a.ne(b) - a != b
* a.gt(b) - a > b
* a.ge(b) - a >= b
* a.lt(b) - a < b
* a.le(b) - a <= b`

> Status: alpha.

$3

- [x] constructors, toString/toFixed
- [x] operations: +|-|*|/
- [x] 4 rounding modes from IEEE 754-1985: RN, RZ, RU, RD
- [x] testing rounding modes with table
- [x] get feedback
- [ ] add benchmark
- [ ] add precision conversion: x.xxxxxxxx BTC in xx.xx $
- [ ] add build with BigInt polyfill