GH38366 [Java][Memory] Fix Murmur hash failing to hash on buffers les…

…s than 4 bytes

java/memory/memory-core/src/main/java/org/apache/arrow/memory/util/hash/MurmurHasher.java

@@ -96,7 +96,7 @@ public static int hashCode(long address, long length, int seed) {
     if (index < length) {
       // process remaining data as a integer in little endian
       int intValue = 0;
-      for (int i = index - 1; i >= index; i--) {
+      for (long i = length - 1; i >= index; i--) {
         intValue <<= 8;
         intValue |= (MemoryUtil.UNSAFE.getByte(address + i) & 0x000000ff);
         index += 1;

java/memory/memory-core/src/test/java/org/apache/arrow/memory/util/hash/TestArrowBufHasher.java

@@ -18,8 +18,10 @@
 package org.apache.arrow.memory.util.hash;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collection;
 
@@ -110,6 +112,26 @@ public void testHasherNegative() {
     }
   }
 
+  @Test
+  public void testHasherLessThanInt() {
+    try (ArrowBuf buf1 = allocator.buffer(4);
+         ArrowBuf buf2 = allocator.buffer(4)) {
+      buf1.writeBytes("foo1".getBytes(StandardCharsets.UTF_8));
+      buf2.writeBytes("bar2".getBytes(StandardCharsets.UTF_8));
+
+      for (int i = 1; i <= 4; i ++) {
+        verifyHashCodeNotEqual(buf1, 0, i, buf2, 0, i);
+      }
+    }
+  }
+
+  private void verifyHashCodeNotEqual(ArrowBuf buf1, int offset1, int length1,
+                                      ArrowBuf buf2, int offset2, int length2) {
+    int hashCode1 = hasher.hashCode(buf1, 0, length1);
+    int hashCode2 = hasher.hashCode(buf2, 0, length2);
+    assertNotEquals(hashCode1, hashCode2);
+  }
+
   @Parameterized.Parameters(name = "hasher = {0}")
   public static Collection<Object[]> getHasher() {
     return Arrays.asList(