server/src/util/Base64.ts

const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+";

// binary to string lookup table
const b2s = alphabet.split("");

// string to binary lookup table
// 123 == 'z'.charCodeAt(0) + 1
const s2b = new Array(123);
for (let i = 0; i < alphabet.length; i++) {
	s2b[alphabet.charCodeAt(i)] = i;
}

// number to base64
export const ntob = (n: number): string => {
	if (n < 0) return `-${ntob(-n)}`;

	let lo = n >>> 0;
	let hi = (n / 4294967296) >>> 0;

	let right = "";
	while (hi > 0) {
		right = b2s[0x3f & lo] + right;
		lo >>>= 6;
		lo |= (0x3f & hi) << 26;
		hi >>>= 6;
	}

	let left = "";
	do {
		left = b2s[0x3f & lo] + left;
		lo >>>= 6;
	} while (lo > 0);

	return left + right;
};

// base64 to number
export const bton = (base64: string) => {
	let number = 0;
	const sign = base64.charAt(0) === "-" ? 1 : 0;

	for (let i = sign; i < base64.length; i++) {
		number = number * 64 + s2b[base64.charCodeAt(i)];
	}

	return sign ? -number : number;
};