Use correct bit masks when extracting low/high word from DWORD

This is a regression introduced by commit 

4218a07

The applied bit masks a 8 bit value, while word is 16 bit sized.

Closes: #624

CHANGES.md

@@ -75,6 +75,7 @@ Bug Fixes
 * [#646](https://github.com/java-native-access/jna/issues/646): `platform.win32.COM.COMBindingBaseObject` swallows reason if instantiation fails - [@matthiasblaesing](https://github.com/matthiasblaesing).
 * [#674](https://github.com/java-native-access/jna/pull/674): Update references to Apache License as requested by issue #673 [@bhamail](https://github.com/bhamail)
 * [#636](https://github.com/java-native-access/jna/issues/636): Staticly link visual c++ runtime when building with MSVC - [@matthiasblaesing](https://github.com/matthiasblaesing).
+* [#624](https://github.com/java-native-access/jna/issues/624): WinDef.DWORD getLow() & getHigh() using incorrect bit mask - [@matthiasblaesing](https://github.com/matthiasblaesing).
 
 Release 4.2.1
 =============

contrib/platform/src/com/sun/jna/platform/win32/WinDef.java

@@ -139,7 +139,7 @@ public DWORD(long value) {
          * @return Low WORD.
          */
         public WORD getLow() {
-            return new WORD(longValue() & 0xFF);
+            return new WORD(longValue() & 0xFFFF);
         }
 
         /**
@@ -148,7 +148,7 @@ public WORD getLow() {
          * @return High WORD.
          */
         public WORD getHigh() {
-            return new WORD((longValue() >> 16) & 0xFF);
+            return new WORD((longValue() >> 16) & 0xFFFF);
         }
 
         @Override

contrib/platform/test/com/sun/jna/platform/win32/WinDefTest.java

@@ -0,0 +1,44 @@
+
+package com.sun.jna.platform.win32;
+
+import com.sun.jna.platform.win32.WinDef.DWORD;
+import com.sun.jna.platform.win32.WinDef.WORD;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class WinDefTest {
+
+    @Test
+    public void testWordExtractionFromDword() {
+        DWORD dword = new DWORD(0x12345678);
+
+        assertEquals(new WORD(0x5678), dword.getLow());
+        assertEquals(new WORD(0x1234), dword.getHigh());
+
+        DWORD dword2 = new DWORD(0xFFFFFFFF);
+
+        assertEquals(new WORD(0xFFFF), dword2.getLow());
+        assertEquals(new WORD(0xFFFF), dword2.getHigh());
+
+        DWORD dword3 = new DWORD(0x00000001);
+
+        assertEquals(new WORD(0x0001), dword3.getLow());
+        assertEquals(new WORD(0x0000), dword3.getHigh());
+
+        DWORD dword4 = new DWORD(0x00010000);
+
+        assertEquals(new WORD(0x0000), dword4.getLow());
+        assertEquals(new WORD(0x0001), dword4.getHigh());
+
+        DWORD dword5 = new DWORD(0x0000FFFF);
+
+        assertEquals(new WORD(0xFFFF), dword5.getLow());
+        assertEquals(new WORD(0x0000), dword5.getHigh());
+
+        DWORD dword6 = new DWORD(0xFFFF0000);
+
+        assertEquals(new WORD(0x0000), dword6.getLow());
+        assertEquals(new WORD(0xFFFF), dword6.getHigh());
+    }
+
+}