1 files changed, 91 insertions, 0 deletions
diff --git a/src/main/java/com/gitblit/utils/IdGenerator.java b/src/main/java/com/gitblit/utils/IdGenerator.java
new file mode 100644
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+++ b/src/main/java/com/gitblit/utils/IdGenerator.java
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+// Copyright (C) 2009 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.gitblit.utils;
+
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import javax.inject.Inject;
+
+/** Simple class to produce 4 billion keys randomly distributed. */
+public class IdGenerator {
+  /** Format an id created by this class as a hex string. */
+  public static String format(int id) {
+    final char[] r = new char[8];
+    for (int p = 7; 0 <= p; p--) {
+      final int h = id & 0xf;
+      r[p] = h < 10 ? (char) ('0' + h) : (char) ('a' + (h - 10));
+      id >>= 4;
+    }
+    return new String(r);
+  }
+
+  private final AtomicInteger gen;
+
+  @Inject
+  public IdGenerator() {
+    gen = new AtomicInteger(new Random().nextInt());
+  }
+
+  /** Produce the next identifier. */
+  public int next() {
+    return mix(gen.getAndIncrement());
+  }
+
+  private static final int salt = 0x9e3779b9;
+
+  static int mix(int in) {
+    return mix(salt, in);
+  }
+
+  /** A very simple bit permutation to mask a simple incrementer. */
+  public static int mix(final int salt, final int in) {
+    short v0 = hi16(in);
+    short v1 = lo16(in);
+    v0 += ((v1 << 2) + 0 ^ v1) + (salt ^ (v1 >>> 3)) + 1;
+    v1 += ((v0 << 2) + 2 ^ v0) + (salt ^ (v0 >>> 3)) + 3;
+    return result(v0, v1);
+  }
+
+  /* For testing only. */
+  static int unmix(final int in) {
+    short v0 = hi16(in);
+    short v1 = lo16(in);
+    v1 -= ((v0 << 2) + 2 ^ v0) + (salt ^ (v0 >>> 3)) + 3;
+    v0 -= ((v1 << 2) + 0 ^ v1) + (salt ^ (v1 >>> 3)) + 1;
+    return result(v0, v1);
+  }
+
+  private static short hi16(final int in) {
+    return (short) ( //
+    ((in >>> 24 & 0xff)) | //
+    ((in >>> 16 & 0xff) << 8) //
+    );
+  }
+
+  private static short lo16(final int in) {
+    return (short) ( //
+    ((in >>> 8 & 0xff)) | //
+    ((in & 0xff) << 8) //
+    );
+  }
+
+  private static int result(final short v0, final short v1) {
+    return ((v0 & 0xff) << 24) | //
+        (((v0 >>> 8) & 0xff) << 16) | //
+        ((v1 & 0xff) << 8) | //
+        ((v1 >>> 8) & 0xff);
+  }
+}