Function decode

lib/util/hash/hash-digest.js:76–108

(data, base)

 * @returns {Buffer} buffer
 */
const decode = (data, base) => {
	if (data.length === 0) return Buffer.from("");
	const alphabet = ENCODE_TABLE[base];
	const bigIntBase = BigInt(alphabet.length);
	// Leading alphabet[0] chars decode back to leading zero bytes (inverse of encode).
	const zeroChar = alphabet[0];
	let zeros = 0;
	while (zeros < data.length && data[zeros] === zeroChar) zeros++;
	// Convert the baseX string to a BigInt value
	let value = ZERO;
	for (let i = 0; i < data.length; i++) {
		const digit = alphabet.indexOf(data[i]);
		if (digit === -1) {
			throw new Error(`Invalid character at position ${i}: ${data[i]}`);
		}
		value = value * bigIntBase + BigInt(digit);
	}
	// Significant byte count of the numeric part (excludes the leading zeros above)
	let temp = value;
	let numLength = 0;
	while (temp > ZERO) {
		temp >>= EIGHT;
		numLength++;
	}
	// Create buffer and fill the numeric part from right to left, leaving the
	// leading `zeros` bytes as 0.
	const buffer = Buffer.alloc(zeros + numLength);
	for (let i = zeros + numLength - 1; i >= zeros; i--) {
		buffer[i] = Number(value & FF);
		value >>= EIGHT;
	}
	return buffer;
};

// Compatibility with the old hash libraries, they can return different structures, so let's stringify them firstly