jni_ vec_ product
fun jni_vec_product(env: CPointer<JNIEnvVar>, thisObject: jobject, a: jdoubleArray, aOffset: jint, aSize: jint): Double
fun jni_vec_product(env: CPointer<JNIEnvVar>, thisObject: jobject, a: jdoubleArray, aOffset: jint, aSize: jint): Double