@isomorphic-pgp/parser/Packet/SignatureSubpacket/Length.js

An OpenPGP message parser

const Uint32 = require("../../Uint32.js");

module.exports.parse = function parse(a) {
  let byte1 = a.b[a.i++];
  if (byte1 < 192) {
    return byte1;
  } else if (byte1 < 255) {
    let byte2 = a.b[a.i++];
    return ((byte1 - 192) << 8) + (byte2 + 192);
  } else {
    return Uint32.parse([a.b[a.i++], a.b[a.i++], a.b[a.i++], a.b[a.i++]]);
  }
}

module.exports.serialize = function serialize(length) {
  if (length < 192) {
    return new Uint8Array([length]);
  } else if (length < 16319) {
    let octet2 = (length - 192) & 255;
    let octet1 = ((length >> 8) + 192) & 255;
    return new Uint8Array([octet1, octet2]);
  } else {
    return new Uint8Array([255, ...Uint32.serialize(length)]);
  }
}