test/jdk/java/nio/Buffer/BasicByte.java

*** 37,46 ****
--- 37,47 ----
  import java.nio.*;
  
  import java.nio.channels.FileChannel;
  import java.nio.file.Files;
  import java.nio.file.Path;
+ import java.util.Random;
  
  
  
  public class BasicByte
      extends Basic
*** 490,499 ****
--- 491,532 ----
                  }
              }
          } catch (IOException e) {
              throw new UncheckedIOException(e);
          }
+ 
+         // alignment identities
+         final int maxPow2 = 12;
+         ByteBuffer bb = ByteBuffer.allocateDirect(1 << maxPow2); // cap 4096
+ 
+         Random rnd = new Random();
+         long seed = rnd.nextLong();
+         rnd = new Random(seed);
+ 
+         for (int i = 0; i < 100; i++) {
+             // 1 == 2^0 <= unitSize == 2^k <= bb.capacity()/2
+             int unitSize = 1 << rnd.nextInt(maxPow2);
+             // 0 <= index < 2*unitSize
+             int index = rnd.nextInt(unitSize << 1);
+             int value = bb.alignmentOffset(index, unitSize);
+             try {
+                 if (value < 0 || value >= unitSize) {
+                     throw new RuntimeException(value + " < 0 || " +
+                         value + " >= " + unitSize);
+                 }
+                 if (value <= index &&
+                     bb.alignmentOffset(index - value, unitSize) != 0)
+                     throw new RuntimeException("Identity 1");
+                 if (bb.alignmentOffset(index + (unitSize - value),
+                     unitSize) != 0)
+                     throw new RuntimeException("Identity 2");
+             } catch (RuntimeException re) {
+                 System.err.format("seed %d, index %d, unitSize %d, value %d%n",
+                     seed, index, unitSize, value);
+                 throw re;
+             }
+         }
      }
  
      private static MappedByteBuffer[] mappedBuffers() throws IOException {
          return new MappedByteBuffer[]{
                  createMappedBuffer(new byte[]{0, 1, 2, 3}),