/* This file is part of VoltDB.
* Copyright (C) 2008-2017 VoltDB Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
package uniquedevices;
import java.util.Random;
public class UniqueIdGenerator {
final int appCount;
final long counts[];
final int nextSubCounts[];
final long realCardinality[];
final int shuffleMap[];
// deterministically seeded PRNG
Random rand = new Random(0);
public UniqueIdGenerator(int appCount) {
this.appCount = appCount;
counts = new long[appCount];
nextSubCounts = new int[appCount];
realCardinality = new long[appCount];
shuffleMap = new int[appCount];
// create a random shuffling map so the distribution of popular
// apps seems random in a top-N list format
for (int i = 0; i < appCount; i++) {
shuffleMap[i] = i;
}
for (int i = 0; i < appCount * 5; i++) {
int index1 = rand.nextInt(appCount);
int index2 = rand.nextInt(appCount);
int temp = shuffleMap[index2];
shuffleMap[index2] = shuffleMap[index1];
shuffleMap[index1] = temp;
}
}
long[] getNextAppIdAndUniqueDeviceId() {
int appId = Integer.MAX_VALUE;
while (appId >= appCount) {
appId = Math.min((int) Math.abs(rand.nextGaussian() * appCount / 3), appCount - 1);
appId = shuffleMap[appId];
}
long value = -1;
while (value < 0) {
int exp = 1 << nextSubCounts[appId];
// possible match
if ((counts[appId] % exp) == 0) {
value = counts[appId];
}
// increment nextSubCounts with a wrap
if (nextSubCounts[appId] == 30) {
nextSubCounts[appId] = 0;
counts[appId]++;
}
else {
nextSubCounts[appId]++;
}
}
if (nextSubCounts[appId] == 1) {
realCardinality[appId]++;
}
return new long[] { appId, value };
}
long expectedCountForApp(int appId) {
return realCardinality[appId];
}
}