reverse bytes before compare

Author: pprudhvi

java/memory/src/main/java/org/apache/arrow/memory/util/ByteFunctionHelpers.java

@@ -140,7 +140,7 @@ private static int memcmp(
       long leftLong = PlatformDependent.getLong(lPos);
       long rightLong = PlatformDependent.getLong(rPos);
       if (leftLong != rightLong) {
-        return unsignedLongCompare(leftLong, rightLong);
+        return unsignedLongCompare(Long.reverseBytes(leftLong), Long.reverseBytes(rightLong));
       }
       lPos += 8;
       rPos += 8;
@@ -151,7 +151,7 @@ private static int memcmp(
       int leftInt = PlatformDependent.getInt(lPos);
       int rightInt = PlatformDependent.getInt(rPos);
       if (leftInt != rightInt) {
-        return unsignedIntCompare(leftInt, rightInt);
+        return unsignedIntCompare(Integer.reverseBytes(leftInt), Integer.reverseBytes(rightInt));
       }
       lPos += 4;
       rPos += 4;

java/memory/src/test/java/org/apache/arrow/memory/util/TestByteFunctionHelpers.java

@@ -111,4 +111,26 @@ public void testCompare() {
     buffer2.close();
 
   }
+
+  @Test
+  public void testStringCompare() {
+    String[] leftStrings = {"cat", "cats", "catworld", "dogs", "bags"};
+    String[] rightStrings = {"dog", "dogs", "dogworld", "dog", "sgab"};
+
+    for (int i = 0; i < leftStrings.length; ++i) {
+      String leftStr = leftStrings[i];
+      String rightStr = rightStrings[i];
+
+      ArrowBuf left = allocator.buffer(SIZE);
+      left.setBytes(0, leftStr.getBytes());
+      ArrowBuf right = allocator.buffer(SIZE);
+      right.setBytes(0, rightStr.getBytes());
+
+      assertEquals(leftStr.compareTo(rightStr) < 0 ? -1 : 1,
+          ByteFunctionHelpers.compare(left, 0, leftStr.length(), right, 0, rightStr.length()));
+
+      left.close();
+      right.close();
+    }
+  }
 }