From b3cc18dbb8158fffc8cc7b8bc26a704a62134046 Mon Sep 17 00:00:00 2001
From: Peter Lawrey <peter.lawrey@chronicle.software>
Date: Tue, 28 Apr 2026 11:26:53 +0100
Subject: [PATCH] Implement support for Math.multiplyHigh in Maths class and
 add JMH benchmarking for XXH3 hashing

---
 pom.xml                                       | 18 +++++++-
 src/main/java/net/openhft/hashing/Maths.java  | 37 +++++----------
 .../hashing/XXH3HashBytesBenchmark.java       | 45 +++++++++++++++++++
 3 files changed, 73 insertions(+), 27 deletions(-)
 create mode 100644 src/test/java/net/openhft/hashing/XXH3HashBytesBenchmark.java

diff --git a/pom.xml b/pom.xml
index 714398b..b2fb805 100644
--- a/pom.xml
+++ b/pom.xml
@@ -38,6 +38,9 @@
         <maven.bundle.plugin.version>5.1.1</maven.bundle.plugin.version>
 
         <doclint>all,-missing</doclint>
+        <jmh.version>1.37</jmh.version>
+        <sonar.organization>openhft</sonar.organization>
+        <sonar.host.url>https://sonarcloud.io</sonar.host.url>
     </properties>
 
     <dependencies>
@@ -74,6 +77,20 @@
             <scope>test</scope>
         </dependency>
 
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh.version}</version>
+            <scope>test</scope>
+        </dependency>
+
     </dependencies>
 
     <build>
@@ -273,7 +290,6 @@
                     </execution>
                 </executions>
             </plugin>
-
         </plugins>
     </build>
 
diff --git a/src/main/java/net/openhft/hashing/Maths.java b/src/main/java/net/openhft/hashing/Maths.java
index 40ed4a0..ee6c251 100644
--- a/src/main/java/net/openhft/hashing/Maths.java
+++ b/src/main/java/net/openhft/hashing/Maths.java
@@ -5,29 +5,26 @@
 
 import org.jetbrains.annotations.NotNull;
 
-import java.lang.invoke.MethodHandle;
-import java.lang.invoke.MethodHandles;
-import java.lang.reflect.Method;
-
+@SuppressWarnings("Since15")
 class Maths {
     @NotNull
     private static final Maths INSTANCE;
 
     static {
-        Maths maths = null;
+        boolean hasMultiplyHigh = true;
         try {
-            Method multiplyHigh = Math.class.getDeclaredMethod("multiplyHigh", int.class, int.class);
-            MethodHandle multiplyHighMH = MethodHandles.lookup().unreflect(multiplyHigh);
-            maths = new MathsJDK9(multiplyHighMH);
+            // stubs in src/main/java-stub are used to allow this to compile in Java 8+
+            Math.multiplyHigh(0, 0);
         } catch (final Throwable ignore) {
-            maths = new Maths();
+            hasMultiplyHigh = false;
         }
-        INSTANCE = maths;
+        INSTANCE = hasMultiplyHigh ? new MathsJDK9() : new Maths();
     }
 
     public static long unsignedLongMulXorFold(final long lhs, final long rhs) {
         return INSTANCE.unsignedLongMulXorFoldImp(lhs, rhs);
     }
+
     public static long unsignedLongMulHigh(final long lhs, final long rhs) {
         return INSTANCE.unsignedLongMulHighImp(lhs, rhs);
     }
@@ -70,31 +67,19 @@ long unsignedLongMulHighImp(final long lhs, final long rhs) {
     }
 }
 
+@SuppressWarnings("Since15")
 class MathsJDK9 extends Maths {
-    private final MethodHandle multiplyHighMH;
-
-    public MathsJDK9(MethodHandle multiplyHighMH) {
-        this.multiplyHighMH = multiplyHighMH;
-    }
-
     // Math.multiplyHigh() is intrinsified from JDK 10. But JDK 9 is out of life, we always prefer
     // this version to the scalar one.
     @Override
     long unsignedLongMulXorFoldImp(final long lhs, final long rhs) {
-        final long upper = invokeExact(lhs, rhs) + ((lhs >> 63) & rhs) + ((rhs >> 63) & lhs);
+        final long upper = Math.multiplyHigh(lhs, rhs) + ((lhs >> 63) & rhs) + ((rhs >> 63) & lhs);
         final long lower = lhs * rhs;
         return lower ^ upper;
     }
+
     @Override
     long unsignedLongMulHighImp(final long lhs, final long rhs) {
-        return invokeExact(lhs, rhs) + ((lhs >> 63) & rhs) + ((rhs >> 63) & lhs);
-    }
-
-    private long invokeExact(long lhs, long rhs) {
-        try {
-            return (long) multiplyHighMH.invokeExact(lhs, rhs);
-        } catch (Throwable e) {
-            throw new AssertionError(e);
-        }
+        return Math.multiplyHigh(lhs, rhs) + ((lhs >> 63) & rhs) + ((rhs >> 63) & lhs);
     }
 }
diff --git a/src/test/java/net/openhft/hashing/XXH3HashBytesBenchmark.java b/src/test/java/net/openhft/hashing/XXH3HashBytesBenchmark.java
new file mode 100644
index 0000000..582e744
--- /dev/null
+++ b/src/test/java/net/openhft/hashing/XXH3HashBytesBenchmark.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2013-2025 chronicle.software; SPDX-License-Identifier: Apache-2.0
+ */
+package net.openhft.hashing;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Reproduces issue #101 for XXH3 hashing of a 128 byte array.
+ */
+@State(Scope.Thread)
+@BenchmarkMode(Mode.Throughput)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Fork(
+        value = 5,
+        warmups = 3,
+        jvmArgs = {
+                "-XX:-TieredCompilation",
+                "-XX:+UseParallelGC",
+                "-Xms16g",
+                "-Xmx16g",
+        })
+public class XXH3HashBytesBenchmark {
+    private static final int INPUT_LENGTH_BYTES = 128;
+    private static final LongHashFunction XXH3_64_HASH_FUNCTION = LongHashFunction.xx3();
+    private static final byte[] ZERO_FILLED_128_BYTE_INPUT = new byte[INPUT_LENGTH_BYTES];
+
+    @Benchmark
+    public long hashZeroFilledByteArray128Bytes() {
+        return XXH3_64_HASH_FUNCTION.hashBytes(ZERO_FILLED_128_BYTE_INPUT);
+    }
+
+    public static void main(String[] args) throws IOException {
+        org.openjdk.jmh.Main.main(args);
+    }
+}