sclass GlobalID implements Comparable<GlobalID> {

  // We need 76 bits for 26^16 IDs

  long a; // lower 64 bits

  int b;  // 76-64=12 higher bits; could be short. change to short when unstructure() is smarter

  *() {}

  *(S id) {

    assertGlobalID(id);

    BigInt value = bigint(0);

    for (int i = 0; i < l(id); i++)

      value = plus(mul(value, 26), charDiff(id.charAt(i), 'a'));

    ifdef GlobalID_debug

    print("value in constructor: " + value);

    endifdef

    a = value.longValue();

    value = value.shiftRight(64);

    b = value.shortValue();

  }

  toString {

    BigInt value = bigint(b);

    value = value.shiftLeft(32);

    value = plus(value, (a >> 32) & 0xFFFFFFFFL);

    value = value.shiftLeft(32);

    value = plus(value, a & 0xFFFFFFFFL);

    ifdef GlobalID_debug

    print("value in toString: " + value);

    endifdef

    ret bigintToGlobalID(value);

  }

  public bool equals(O o) {

    if (!o instanceof GlobalID) false;

    ret o/GlobalID.a == a && o/GlobalID.b == b;

  }

  public int hashCode() {

    ret (int) a;

  }

  // matches ID's lexical ordering

  public int compareTo(GlobalID id) {

    int diff = b-id.b;

    ret diff != 0 ? diff : Long.compareUnsigned(a, id.a);

  }

}