[Bug-Fix] Fixing the Quantization to clone the quantized vector, prep…

…are the quantized vector correctly.

Signed-off-by: Navneet Verma <navneev@amazon.com>

src/main/java/org/opensearch/knn/index/codec/nativeindex/QuantizationIndexUtils.java

@@ -33,7 +33,8 @@ static Object processAndReturnVector(KNNVectorValues<?> knnVectorValues, IndexBu
                 knnVectorValues.getVector(),
                 indexBuildSetup.getQuantizationOutput()
             );
-            return indexBuildSetup.getQuantizationOutput().getQuantizedVector();
+            // We should get the cloned Vector because Quantization output always have the same reference
+            return indexBuildSetup.getQuantizationOutput().cloneQuantizedVector();
         } else {
             return knnVectorValues.conditionalCloneVector();
         }

src/main/java/org/opensearch/knn/quantization/models/quantizationOutput/BinaryQuantizationOutput.java

@@ -54,6 +54,13 @@ public boolean isPrepared(int vectorLength) {
         return vectorLength == currentVectorLength && quantizedVector != null;
     }
 
+    @Override
+    public byte[] cloneQuantizedVector() {
+        byte[] clonedByteArray = new byte[quantizedVector.length];
+        System.arraycopy(quantizedVector, 0, clonedByteArray, 0, quantizedVector.length);
+        return clonedByteArray;
+    }
+
     /**
      * Returns the quantized vector.
      *

src/main/java/org/opensearch/knn/quantization/models/quantizationOutput/QuantizationOutput.java

@@ -33,4 +33,6 @@ public interface QuantizationOutput<T> {
      * @return true if the quantized vector is already prepared, false otherwise.
      */
     boolean isPrepared(int vectorLength);
+
+    T cloneQuantizedVector();
 }

src/main/java/org/opensearch/knn/quantization/quantizer/OneBitScalarQuantizer.java

@@ -84,7 +84,8 @@ public void quantize(final float[] vector, final QuantizationState state, final
         if (thresholds == null || thresholds.length != vectorLength) {
             throw new IllegalArgumentException("Thresholds must not be null and must match the dimension of the vector.");
         }
-        if (!output.isPrepared(vectorLength)) output.prepareQuantizedVector(vectorLength);
+        // This will ensure that we are preparing the Quantized Vector always. aka setting all the bits to 0.
+        output.prepareQuantizedVector(vectorLength);
         BitPacker.quantizeAndPackBits(vector, thresholds, output.getQuantizedVector());
     }