base85

class base85 {
  encode(input) {
    const encoded = [];
    const chunkSize = 4;
    for (let i = 0; i < input.length; i += chunkSize) {
      const chunk = input.substr(i, chunkSize).padEnd(chunkSize, "\0");
      let value = 0;
      for (let j = 0; j < chunk.length; j++) {
        value = (value << 8) + chunk.charCodeAt(j);
      }
      for (let j = 4; j >= 0; j--) {
        encoded.push(String.fromCharCode(33 + ((value / 85 ** j) % 85)));
      }
    }
    return encoded.join("");
  }

  decode(input) {
    const decoded = [];
    const chunkSize = 5;
    for (let i = 0; i < input.length; i += chunkSize) {
      const chunk = input.substr(i, chunkSize).padEnd(chunkSize, "u");
      let value = 0;
      for (let j = 0; j < chunk.length; j++) {
        value = value * 85 + (chunk.charCodeAt(j) - 33);
      }
      for (let j = 3; j >= 0; j--) {
        decoded.push(String.fromCharCode((value >> (8 * j)) & 255));
      }
    }
    return decoded.join("").replace(/\0+$/, "");
  }

  matches(input) {
    const base85Regex = /^[\x21-\x75]{10,}$/;
    const result = base85Regex.exec(input);
    return result ? result : null;
  }
}