endian-code/index.js

Encodes and decodes numbers of given size in big and little endian.

module.exports = {
	encode: function (n, k, bigEndian) {
		if (n < 0)
			n = parseInt('0x1' + '00'.repeat(k)) + n;
		let str = n.toString(16);
		if (str.length % 2 === 1) {
			str = '0' + str;
		}
		let encoded = str.match(/.{1,2}/g).map(x => parseInt(x, 16));
		return bigEndian
			? new Array(k - encoded.length).fill(0).concat(encoded)
			: encoded.reverse().concat(new Array(k - encoded.length).fill(0));
	},
	decode: function (arr, k, bigEndian) {
		arr = [...arr];
		let res = parseInt('0x' + (bigEndian ? arr.concat(new Array(k - arr.length).fill(0)) : new Array(k - arr.length).fill(0).concat(arr.reverse())).
			reduce((total, next) => total += next.toString(16).padStart(2, '0'), ''), 16);
		if (res >= parseInt('0x80' + '00'.repeat(k - 1)))
			res = res - parseInt('0x1' + '00'.repeat(k));

		return res;
	}
}