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+/*
+ * Copyright (C) 2013 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.
+ */
+
+#ifndef LE_FX_ENGINE_DSP_CORE_INTERPOLATOR_BASE_H_
+#define LE_FX_ENGINE_DSP_CORE_INTERPOLATOR_BASE_H_
+
+#include "common/core/types.h"
+
+namespace le_fx {
+
+namespace sigmod {
+
+// Interpolation base-class that provides the interface, while it is the derived
+// class that provides the specific interpolation algorithm. The following list
+// of interpolation algorithms are currently present:
+//
+// InterpolationSine<T>: weighted interpolation between y_data[n] and
+//                       y_data[n+1] using a sin(.) weighting factor from
+//                       0 to pi/4.
+// InterpolationLinear<T>: linear interpolation
+// InterpolationSplines<T>: spline-based interpolation
+//
+// Example (using derived spline-based interpolation class):
+//  InterpolatorSplines<float> interp(x_data, y_data, data_length);
+//  for (int n = 0; n < data_length; n++) Y[n] = interp.Interpolate(X[n]);
+//
+template <typename T, class Algorithm>
+class InterpolatorBase {
+ public:
+  InterpolatorBase();
+  ~InterpolatorBase();
+
+  // Generic random-access interpolation with arbitrary spaced x-axis samples.
+  // Below X[0], the interpolator returns Y[0]. Above X[data_length-1], it
+  // returns Y[data_length-1].
+  T Interpolate(T x);
+
+  bool get_status() const {
+    return status_;
+  }
+
+  // Initializes internal buffers.
+  //  x_data: [(data_length)x1] x-axis coordinates (searching axis)
+  //  y_data: [(data_length)x1] y-axis coordinates (interpolation axis)
+  //  data_length: number of points
+  // returns `true` if everything is ok, `false`, otherwise
+  bool Initialize(const T *x_data, const T *y_data, int data_length);
+
+  // Initializes internal buffers.
+  //  x_data: x-axis coordinates (searching axis)
+  //  y_data: y-axis coordinates (interpolating axis)
+  // returns `true` if everything is ok, `false`, otherwise
+  bool Initialize(const vector<T> &x_data, const vector<T> &y_data);
+
+  // Initialization for regularly sampled sequences, where:
+  //  x_data[i] = x_start_offset + i * x_sampling_interval
+  bool Initialize(double x_start_offset,
+                  double x_sampling_interval,
+                  const vector<T> &y_data);
+
+  // Initialization for regularly sampled sequences, where:
+  //  x_data[i] = x_start_offset + i * x_sampling_interval
+  bool Initialize(double x_start_offset,
+                  double x_sampling_interval,
+                  const T *y_data,
+                  int data_length);
+
+ protected:
+  // Is set to false if something goes wrong, and to true if everything is ok.
+  bool status_;
+
+  // The start-index of the previously searched interval
+  int cached_index_;
+
+  // Data points
+  const T *x_data_;  // Externally or internally owned, depending on own_x_data_
+  const T *y_data_;  // Externally owned (always)
+  int data_length_;
+  // Index of the last element `data_length_ - 1` kept here for optimization
+  int last_element_index_;
+  bool own_x_data_;
+  // For regularly-samples sequences, keep only the boundaries and the intervals
+  T x_start_offset_;
+  float x_inverse_sampling_interval_;
+
+  // Algorithm state (internally owned)
+  double *state_;
+
+ private:
+  LE_FX_DISALLOW_COPY_AND_ASSIGN(InterpolatorBase);
+};
+
+}  // namespace sigmod
+
+}  // namespace le_fx
+
+#include "dsp/core/interpolator_base-inl.h"
+
+#endif  // LE_FX_ENGINE_DSP_CORE_INTERPOLATOR_BASE_H_