randomUid function
Returns a uniformly pseudorandom UID u such that -263 <= u < 0 or 2 < u < 263
Implementation
Int64 randomUid(math.Random prng) {
var answer = Int64.ZERO;
while (answer == Int64.ZERO || answer == inboxUid || answer == rootFolderUid) {
answer = Int64.fromInts(_next32bitInt(prng), _next32bitInt(prng));
}
return answer;
}