Some common functions for modular arithmetic using native JS implementation of BigInt

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Some extra functions to work with modular arithmetic using native JS (ES-2020) implementation of BigInt. It can be used by any Web Browser or webview supporting BigInt and with Node.js (>=10.4.0).
The operations supported on BigInts are not constant time. BigInt can be therefore unsuitable for use in cryptography. Many platforms provide native support for cryptography, such as Web Cryptography API or Node.js Crypto.


bigint-mod-arith can be imported to your project with npm:
npm install bigint-mod-arith

Then either require (Node.js CJS):
const bigintModArith = require('bigint-mod-arith')

Node >=10.4 <11. bigint-mod-arith uses workers to speed up some operations. Workers are enabled by default with Node.js from version 11. In order to use them with Node >=10.4 and <11, you need to execute node with the flag --experimental-worker, and require the .js file manually (otherwise .cjs is required by default and would not be supported by the workers)
const bigintCryptoUtils = require('bigint-crypto-utils/dist/cjs/index.node')  // ONLY FOR node >=10.4 <11 !

or import (JavaScript ES module):
import * as bigintModArith from 'bigint-mod-arith'

The appropriate version for browser or node is automatically exported.
You can also download the IIFE bundle, the ESM bundle or the UMD bundle and manually add it to your project, or, if you have already imported bigint-mod-arith to your project, just get the bundles from node_modules/bigint-mod-arith/dist/bundles/.
An example of usage could be:
/* Stage 3 BigInts with value 666 can be declared as BigInt('666')
or the shorter syntax 666n.
Notice that you can also pass a number, e.g. BigInt(666), but it is not
recommended since values over 2**53 - 1 won't be safe but no warning will
be raised.
const a = BigInt('5')
const b = BigInt('2')
const n = 19n

console.log(bigintModArith.modPow(a, b, n)) // prints 6

console.log(bigintModArith.modInv(2n, 5n)) // prints 3

console.log(bigintModArith.modInv(BigInt('3'), BigInt('5'))) // prints 2

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