fix Decimal equals

Author: tianchen92

java/vector/src/main/java/org/apache/arrow/vector/DecimalVector.java

@@ -22,6 +22,7 @@
 import java.math.BigDecimal;
 
 import org.apache.arrow.memory.BufferAllocator;
+import org.apache.arrow.memory.util.ByteFunctionHelpers;
 import org.apache.arrow.vector.complex.impl.DecimalReaderImpl;
 import org.apache.arrow.vector.complex.reader.FieldReader;
 import org.apache.arrow.vector.holders.DecimalHolder;
@@ -489,6 +490,36 @@ public void setSafe(int index, int isSet, int start, ArrowBuf buffer) {
     set(index, isSet, start, buffer);
   }
 
+  @Override
+  public boolean equals(int index, ValueVector to, int toIndex) {
+    if (to == null) {
+      return false;
+    }
+    if (this.getMinorType() != to.getMinorType()) {
+      return false;
+    }
+
+    DecimalVector that = (DecimalVector) to;
+
+    if (this.scale != that.scale || this.precision != that.precision) {
+      return false;
+    }
+
+    if (this.isSet(index) != that.isSet(toIndex)) {
+      return false;
+    }
+
+    int leftStart = TYPE_WIDTH * index;
+    int leftEnd = TYPE_WIDTH * (index + 1);
+
+    int rightStart = TYPE_WIDTH * toIndex;
+    int rightEnd = TYPE_WIDTH * (toIndex + 1);
+
+    int ret = ByteFunctionHelpers.equal(this.getDataBuffer(), leftStart, leftEnd,
+        that.getDataBuffer(), rightStart, rightEnd);
+    return ret == 1;
+  }
+
 
   /*----------------------------------------------------------------*
    |                                                                |

java/vector/src/test/java/org/apache/arrow/vector/TestValueVector.java

@@ -2282,6 +2282,33 @@ public void testIntVectorEquals() {
     }
   }
 
+  @Test
+  public void testDecimalVectorEquals() {
+    try (final DecimalVector vector1 = new DecimalVector("v1", allocator, 3, 3);
+        final DecimalVector vector2 = new DecimalVector("v2", allocator, 3, 3);
+        final DecimalVector vector3 = new DecimalVector("v3", allocator, 3, 2)) {
+
+      vector1.allocateNew(2);
+      vector1.setValueCount(2);
+      vector2.allocateNew(2);
+      vector2.setValueCount(2);
+      vector3.allocateNew(2);
+      vector3.setValueCount(2);
+
+      vector1.setSafe(0, 100);
+      vector1.setSafe(1, 200);
+
+      vector2.setSafe(0, 100);
+      vector2.setSafe(1, 200);
+
+      vector3.setSafe(0, 100);
+      vector3.setSafe(1, 200);
+
+      assertTrue(vector1.equals(vector2));
+      assertFalse(vector1.equals(vector3));
+    }
+  }
+
   @Test
   public void testVarcharVectorEquals() {
     try (final VarCharVector vector1 = new VarCharVector("v1", allocator);