[GitHub] [pinot] tivrfoa commented on a change in pull request #7487: use MethodHandle to access vectorized unsigned comparison on JDK9+

[GitBox <gi...@apache.org>]

tivrfoa commented on a change in pull request #7487:
URL: https://github.com/apache/pinot/pull/7487#discussion_r719368071



##########
File path: pinot-spi/src/main/java/org/apache/pinot/spi/utils/ByteArray.java
##########
@@ -91,19 +115,55 @@ public int compareTo(@Nonnull ByteArray that) {
    *   <li> +ve integer if first value is larger than the second. </li>
    * </ul>
    *
-   * @param bytes1 First byte[] to compare.
-   * @param bytes2 Second byte[] to compare.
+   * @param left First byte[] to compare.
+   * @param right Second byte[] to compare.
    * @return Result of comparison as stated above.
    */
-  public static int compare(byte[] bytes1, byte[] bytes2) {
-    int len1 = bytes1.length;
-    int len2 = bytes2.length;
+  public static int compare(byte[] left, byte[] right) {
+    return compare(left, 0, left.length, right, 0, right.length);
+  }
+
+  /**
+   * Compares two byte[] values. The comparison performed is on unsigned value for each byte.
+   * Returns:
+   * <ul>
+   *   <li> 0 if both values are identical. </li>
+   *   <li> -ve integer if first value is smaller than the second. </li>
+   *   <li> +ve integer if first value is larger than the second. </li>
+   * </ul>
+   *
+   * @param left First byte[] to compare.
+   * @param leftFromIndex inclusive index of first byte to compare in left
+   * @param leftToIndex exclusive index of last byte to compare in left
+   * @param right Second byte[] to compare.
+   * @param rightFromIndex inclusive index of first byte to compare in right
+   * @param rightToIndex exclusive index of last byte to compare in right
+   * @return Result of comparison as stated above.
+   */
+  public static int compare(byte[] left, int leftFromIndex, int leftToIndex,
+      byte[] right, int rightFromIndex, int rightToIndex) {
+    if (COMPARE_UNSIGNED != null) {

Review comment:
       Hi folks!
   
   I was going to ask the question below, but then I understood why MethodHandle lookup was used.
   Very nice idea! Multi-release jar is very nice too! =)
   
   ---
   
   Newbie question:<br>
   I need to compile with java version >= 9 to use Arrays.compareUnsigned, but if I run with Java 8 I get:<br>
   
   ```
   Error: A JNI error has occurred, please check your installation and try again
   Exception in thread "main" java.lang.UnsupportedClassVersionError: JavaVersion has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
   
   or
   
     bad class file: ./JavaVersion.class
       class file has wrong version 55.0, should be 52.0
       Please remove or make sure it appears in the correct subdirectory of the classpath.
   ```
   
   So what's the point to prepare the code for a previous version?<br>
   
   ps: I'm sure I'm missing something. =D




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