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diff --git a/firmware/os/algos/calibration/online_calibration/common_data/calibration_callback.h b/firmware/os/algos/calibration/online_calibration/common_data/calibration_callback.h
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+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * This module provides the callback functionality employed by the online sensor
+ * calibration algorithms.
+ */
+
+#ifndef LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_ONLINE_CALIBRATION_COMMON_DATA_CALIBRATION_CALLBACK_H_
+#define LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_ONLINE_CALIBRATION_COMMON_DATA_CALIBRATION_CALLBACK_H_
+
+#include "calibration/online_calibration/common_data/calibration_data.h"
+
+namespace online_calibration {
+
+/*
+ * This codebase avoids Standard Template Library (STL) containers to maximize
+ * its usefullness on embedded hardware with basic C++ compiler support. The
+ * following uses type erasure to implement callback functionality to a user's
+ * desired class method. The idea here is to store an object pointer by
+ * instantiating a class template (Callback) which implements a virtual
+ * interface function (CallbackInterface::Call).
+ *
+ * USAGE:
+ * See unit testing for a simple example of how to use this for callback
+ * functionality.
+ */
+
+// CalibrationType: Sets the calibration type (e.g., CalibrationDataThreeAxis).
+template <class CalibrationType>
+class CallbackInterface {
+ public:
+  // Interface function that is defined to implement the desired callback.
+  virtual void Call(const CalibrationType& cal_data,
+                    CalibrationTypeFlags cal_update_flags) = 0;
+  virtual ~CallbackInterface() {}
+};
+
+// ClassCallerType: Sets the object's class type for the callback.
+// CalibrationType: Sets the calibration type (e.g., CalibrationDataThreeAxis).
+template <class ClassCallerType, class CalibrationType>
+class Callback : public CallbackInterface<CalibrationType> {
+ public:
+  // Constructors.
+  Callback() = delete;
+  Callback(ClassCallerType* obj,
+           void (ClassCallerType::*func)(const CalibrationType& cal_data,
+                                         CalibrationTypeFlags cal_update_flags))
+      : object_ptr_(obj), function_ptr_(func) {}
+
+  // Implements the callback to the desired class-method.
+  void Call(const CalibrationType& cal_data,
+            CalibrationTypeFlags cal_update_flags) final {
+    (object_ptr_->*function_ptr_)(cal_data, cal_update_flags);
+  }
+
+ private:
+  // Pointer to the class that owns the callback method.
+  ClassCallerType* object_ptr_;
+
+  // Templated function pointer with the required function signature.
+  // Calibration callbacks must accept:
+  //   1. Constant reference to the calibration.
+  //   2. Bitmask indicating which calibration components have been updated.
+  void (ClassCallerType::*function_ptr_)(const CalibrationType& cal_data,
+                                         CalibrationTypeFlags cal_update_flags);
+};
+
+}  // namespace online_calibration
+
+#endif  // LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_ONLINE_CALIBRATION_COMMON_DATA_CALIBRATION_CALLBACK_H_