LUCENE-10572: Add support for varhandles in native byte order (still randomized during tests) (#888)

lucene/CHANGES.txt

@@ -212,6 +212,10 @@ Improvements
 
 * GITHUB#13055: Make DEFAULT_STOP_TAGS in KoreanPartOfSpeechStopFilter immutable (Dmitry Cherniachenko)
 
+* GITHUB#888: Use native byte order varhandles to spare CPU's byte swapping.
+  Tests are running with random byte order to ensure that the order does not affect correctness
+  of code. Native order was enabled for LZ4 compression.  (Uwe Schindler)
+
 Optimizations
 ---------------------
 

lucene/core/src/java/org/apache/lucene/util/BitUtil.java

@@ -29,6 +29,29 @@ public final class BitUtil {
 
   private BitUtil() {} // no instance
 
+  /**
+   * Native byte order.
+   *
+   * <p>Warning: This constant is {@link ByteOrder#nativeOrder()} only in production environments,
+   * during testing we randomize it. If you need to communicate with native APIs (e.g., Java's
+   * Panama API), use {@link ByteOrder#nativeOrder()}.
+   */
+  public static final ByteOrder NATIVE_BYTE_ORDER = getNativeByteOrder();
+
+  private static ByteOrder getNativeByteOrder() {
+    try {
+      var prop = System.getProperty("tests.seed");
+      if (prop != null) {
+        return (prop.hashCode() % 2 == 0) ? ByteOrder.LITTLE_ENDIAN : ByteOrder.BIG_ENDIAN;
+      }
+    } catch (
+        @SuppressWarnings("unused")
+        SecurityException se) {
+      // fall-through
+    }
+    return ByteOrder.nativeOrder();
+  }
+
   /**
    * A {@link VarHandle} to read/write little endian {@code short} from/to a byte array. Shape:
    * {@code short vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, short
@@ -65,6 +88,62 @@ public final class BitUtil {
   public static final VarHandle VH_LE_DOUBLE =
       MethodHandles.byteArrayViewVarHandle(double[].class, ByteOrder.LITTLE_ENDIAN);
 
+  /**
+   * A {@link VarHandle} to read/write native endian {@code short} from/to a byte array. Shape:
+   * {@code short vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, short
+   * val)}
+   *
+   * <p>Warning: This handle uses default order only in production environments, during testing we
+   * randomize it. If you need to communicate with native APIs (e.g., Java's Panama API), use {@link
+   * ByteOrder#nativeOrder()}.
+   */
+  public static final VarHandle VH_NATIVE_SHORT =
+      MethodHandles.byteArrayViewVarHandle(short[].class, NATIVE_BYTE_ORDER);
+
+  /**
+   * A {@link VarHandle} to read/write native endian {@code int} from a byte array. Shape: {@code
+   * int vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, int val)}
+   *
+   * <p>Warning: This handle uses default order only in production environments, during testing we
+   * randomize it. If you need to communicate with native APIs (e.g., Java's Panama API), use {@link
+   * ByteOrder#nativeOrder()}.
+   */
+  public static final VarHandle VH_NATIVE_INT =
+      MethodHandles.byteArrayViewVarHandle(int[].class, NATIVE_BYTE_ORDER);
+
+  /**
+   * A {@link VarHandle} to read/write native endian {@code long} from a byte array. Shape: {@code
+   * long vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, long val)}
+   *
+   * <p>Warning: This handle uses default order only in production environments, during testing we
+   * randomize it. If you need to communicate with native APIs (e.g., Java's Panama API), use {@link
+   * ByteOrder#nativeOrder()}.
+   */
+  public static final VarHandle VH_NATIVE_LONG =
+      MethodHandles.byteArrayViewVarHandle(long[].class, NATIVE_BYTE_ORDER);
+
+  /**
+   * A {@link VarHandle} to read/write native endian {@code float} from a byte array. Shape: {@code
+   * float vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, float val)}
+   *
+   * <p>Warning: This handle uses default order only in production environments, during testing we
+   * randomize it. If you need to communicate with native APIs (e.g., Java's Panama API), use {@link
+   * ByteOrder#nativeOrder()}.
+   */
+  public static final VarHandle VH_NATIVE_FLOAT =
+      MethodHandles.byteArrayViewVarHandle(float[].class, NATIVE_BYTE_ORDER);
+
+  /**
+   * A {@link VarHandle} to read/write native endian {@code double} from a byte array. Shape: {@code
+   * double vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, double val)}
+   *
+   * <p>Warning: This handle uses default order only in production environments, during testing we
+   * randomize it. If you need to communicate with native APIs (e.g., Java's Panama API), use {@link
+   * ByteOrder#nativeOrder()}.
+   */
+  public static final VarHandle VH_NATIVE_DOUBLE =
+      MethodHandles.byteArrayViewVarHandle(double[].class, NATIVE_BYTE_ORDER);
+
   /**
    * A {@link VarHandle} to read/write big endian {@code short} from a byte array. Shape: {@code
    * short vh.get(byte[] arr, int ofs)} and {@code void vh.set(byte[] arr, int ofs, short val)}

lucene/core/src/java/org/apache/lucene/util/compress/LZ4.java

@@ -68,10 +68,8 @@ public final class LZ4 {
   }
 
   private static int readInt(byte[] buf, int i) {
-    // we hardcode LITTLE ENDIAN here as this is most performant on most platforms.
-    // According to LZ4's alogrithm the endianness does not matter at all, but we
-    // want to prevent indexes to differ just because of platform endianness!
-    return (int) BitUtil.VH_LE_INT.get(buf, i);
+    // According to LZ4's algorithm the endianness does not matter at all:
+    return (int) BitUtil.VH_NATIVE_INT.get(buf, i);
   }
 
   private static int commonBytes(byte[] b, int o1, int o2, int limit) {