[WIP] Add MultiVectorField For Late-interaction Score

src/main/java/org/opensearch/knn/index/MultiVectorField.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.knn.index;
+
+import org.apache.lucene.document.Field;
+import org.apache.lucene.index.IndexableFieldType;
+import org.apache.lucene.util.BytesRef;
+import org.opensearch.knn.index.codec.util.KNNVectorAsCollectionOfFloatsSerializer;
+import org.opensearch.knn.index.codec.util.KNNVectorSerializer;
+
+import java.nio.ByteBuffer;
+import java.util.List;
+
+public class MultiVectorField extends Field{
+
+
+    public MultiVectorField(String name, List<float[]> value, IndexableFieldType type) {
+        super(name, new BytesRef(), type);
+        try {
+            final KNNVectorSerializer vectorSerializer = KNNVectorAsCollectionOfFloatsSerializer.INSTANCE;
+            final ByteBuffer floatToByte = vectorSerializer.floatsToByteArray(value);
+            this.setBytesValue(floatToByte.array());
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * @param name FieldType name
+     * @param value multi arrays of byte vector values
+     * @param type FieldType to build DocValues
+     */
+    public MultiVectorField(String name, byte[] value, IndexableFieldType type) {
+        super(name, new BytesRef(), type);
+        try {
+            this.setBytesValue(value);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+}

src/main/java/org/opensearch/knn/index/codec/util/KNNVectorAsCollectionOfFloatsSerializer.java

@@ -9,6 +9,8 @@
 
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.stream.IntStream;
 
 /**
@@ -38,4 +40,38 @@ public float[] byteToFloatArray(BytesRef bytesRef) {
         ByteBuffer.wrap(bytesRef.bytes, bytesRef.offset, bytesRef.length).asFloatBuffer().get(vector);
         return vector;
     }
+
+    @Override
+    public ByteBuffer floatsToByteArray(List<float[]> input) {
+        //TODO
+        if (input.isEmpty()) {
+            return null;
+        }
+        int bufferSize = input.size() * input.get(0).length * BYTES_IN_FLOAT;
+        final ByteBuffer bb = ByteBuffer.allocate(bufferSize).order(ByteOrder.BIG_ENDIAN);
+
+        for (float[] vector : input) {
+            for(float f : vector) {
+                bb.putFloat(f);
+            }
+        }
+        return bb;
+    }
+
+    @Override
+    public List<float[]> byteToFloatsArray(BytesRef bytesRef, int dims) {
+        if (bytesRef == null || bytesRef.length % BYTES_IN_FLOAT != 0) {
+            throw new IllegalArgumentException("Byte stream cannot be deserialized to arrays of floats");
+        }
+        final int sizeOfFloatArray = bytesRef.length / BYTES_IN_FLOAT;
+        int number_vectors = sizeOfFloatArray / dims;
+        List<float[]> vectors = new ArrayList<>();
+        for (int i = 0, offset = 0; i < number_vectors; i++) {
+            final float[] vector = new float[dims];
+            ByteBuffer.wrap(bytesRef.bytes, offset, dims * BYTES_IN_FLOAT).asFloatBuffer().get(vector);
+            vectors.add(vector);
+            offset += dims * BYTES_IN_FLOAT;
+        }
+        return vectors;
+    }
 }

src/main/java/org/opensearch/knn/index/codec/util/KNNVectorSerializer.java

@@ -7,6 +7,9 @@
 
 import org.apache.lucene.util.BytesRef;
 
+import java.nio.ByteBuffer;
+import java.util.List;
+
 /**
  * Interface abstracts the vector serializer object that is responsible for serialization and de-serialization of k-NN vector
  */
@@ -25,4 +28,20 @@ public interface KNNVectorSerializer {
      * @return array of floats deserialized from the stream
      */
     float[] byteToFloatArray(BytesRef bytesRef);
+
+    /**
+     * Serializes multi array of floats to array of bytes
+     * @param input multi array that will be converted
+     * @return array of bytes that contains serialized input array
+     */
+    ByteBuffer floatsToByteArray(List<float[]> input);
+
+    /**
+     * Deserializes all bytes from the stream to multi array of floats
+     *
+     * @param bytesRef bytes that will be used for deserialization to array of floats
+     * @return array of floats deserialized from the stream
+     */
+    List<float[]> byteToFloatsArray(BytesRef bytesRef, int dims);
+
 }