A library for arbitrary precision decimal floating point arithmetic that can exactly represent all decimal fractions, unlike JavaScript’s number data type which is 64-bit binary floating point.

Based on the original work by Douglas Crockford. This implementation is built upon ES native bigints.

This library provides three ways to make bigfloat operations:

A set of functions for a functional style approach
A BigFloat class with an API similar to that of Decimal.js
An evaluate() function that parses and resolves an expression

Basic usage

Functional style

import { make, string, sqrt } from "https://deno.land/x/bigfloat/mod.ts";

string(sqrt(make("2")));               // "1.4142"

Class based

import { BigFloat } from "https://deno.land/x/bigfloat/mod.ts";

new BigFloat("2").sqrt().toString();   // "1.4142"

The evaluate() function

evaluate(expression: string, precision?: number): string | boolean

The first argument can be any valid arithmetic or relational expression, including scientific e-notation. Precision should be a negative integer. Default is -4.

import { evaluate } from "https://deno.land/x/bigfloat/mod.ts";

0.1 + 0.2 === 0.3;                     // false
evaluate("0.1 + 0.2 == 0.3");          // true

0.1 + 0.2;                             // 0.30000000000000004
evaluate("0.1 + 0.2");                 // "0.3"

1 + Number.EPSILON / 2;                // 1
evaluate(`1 + ${Number.EPSILON / 2}`); // "1.00000000000000011102230246251565"

evaluate("1 + 2.220446049250313e-16"); // "1.0000000000000002220446049250313"

evaluate(`4 >= ${Math.PI}`);           // true

Valid tokens:

Parenthesis: (,)
Number: Decimal, integer or scientific e-notation
Operator: Arithmetic +,-,/,*,** Relational ===,==,!==,!=,<,>,<=,>=

Change precision

import { BigFloat, set_precision } from "https://deno.land/x/bigfloat/mod.ts";

new BigFloat(2).sqrt().toString();     // "1.4142"
set_precision(-10);
new BigFloat(2).sqrt().toString();     // "1.4142135623"

The bigfloat object

interface IBigFloat {
  coefficient: bigint;
  exponent: number;
}

Valid bigfloat made from primitives:

const bigfloat: IBigFloat {
  coefficient: 522299n,
  exponent: -4
};