8282144: RandomSupport.convertSeedBytesToLongs sign extension overwrites previous bytes

Reviewed-by: bpb

src/java.base/share/classes/jdk/internal/util/random/RandomSupport.java

@@ -265,7 +265,7 @@ public class RandomSupport {
         final int m = Math.min(seed.length, n << 3);
         // Distribute seed bytes into the words to be formed.
         for (int j = 0; j < m; j++) {
-            result[j>>3] = (result[j>>3] << 8) | seed[j];
+            result[j>>3] = (result[j>>3] << 8) | (seed[j] & 0xFF);
         }
         // If there aren't enough seed bytes for all the words we need,
         // use a SplitMix-style PRNG to fill in the rest.

test/jdk/java/util/Random/T8282144.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.util.random.*;
+import jdk.internal.util.random.RandomSupport;
+
+/**
+ * @test
+ * @summary RandomSupport.convertSeedBytesToLongs sign extension overwrites previous bytes.
+ * @bug 8282144
+ * @modules java.base/jdk.internal.util.random
+ * @run main T8282144
+ * @key randomness
+ */
+
+
+public class T8282144 {
+    public static void main(String[] args) {
+        RandomGenerator rng = RandomGeneratorFactory.of("L64X128MixRandom").create(42);
+
+        for (int i = 1; i < 8; i++) {
+            byte[] seed = new byte[i];
+
+            for (int j = 0; j < 10; j++) {
+                rng.nextBytes(seed);
+
+                long[] existing = RandomSupport.convertSeedBytesToLongs(seed, 1, 1);
+                long[] testing = convertSeedBytesToLongsFixed(seed, 1, 1);
+
+                for (int k = 0; k < existing.length; k++) {
+                    if (existing[k] != testing[k]) {
+                        throw new RuntimeException("convertSeedBytesToLongs incorrect");
+                    }
+                }
+            }
+        }
+    }
+
+
+    public static long[] convertSeedBytesToLongsFixed(byte[] seed, int n, int z) {
+        final long[] result = new long[n];
+        final int m = Math.min(seed.length, n << 3);
+
+        // Distribute seed bytes into the words to be formed.
+        for (int j = 0; j < m; j++) {
+            result[j >> 3] = (result[j >> 3] << 8) | (seed[j] & 0xff);
+        }
+
+        return result;
+    }
+}