Handle near-colinear case in WSOLAS QuadraticInterpolation better.

media/filters/wsola_internals.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A set of utility functions to perform WSOLA.
 
 #ifndef MEDIA_FILTERS_WSOLA_INTERNALS_H_
 #define MEDIA_FILTERS_WSOLA_INTERNALS_H_
 
 #include <utility>
@@ skipping 20 matching lines @@
 
 // Energies of sliding windows of channels are interleaved.
 // The number windows is |input->frames()| - (|frames_per_window| - 1), hence,
 // the method assumes |energy| must be, at least, of size
 // (|input->frames()| - (|frames_per_window| - 1)) * |input->channels()|.
 MEDIA_EXPORT void MultiChannelMovingBlockEnergies(const AudioBus* input,
                                                   int frames_per_window,
                                                   float* energy);
 
 // Fit the curve f(x) = a * x^2 + b * x + c such that
-//
-// f(-1) = |y[0]|
-// f(0) = |y[1]|
-// f(1) = |y[2]|.
-//
-// Then compute the |extremum| point -b / (2*a) and |extremum_value|
-// b^2 / (4*a) - b^2 / (2*a) + c.
-//
-// It is not expected that this function is called with
-// y[0] == y[1] == y[2].
-MEDIA_EXPORT void CubicInterpolation(const float* y_values,
-                                     float* extremum,
-                                     float* extremum_value);
+//   f(-1) = y[0]
+//   f(0) = y[1]
+//   f(1) = y[2]
+// and return the maximum, assuming that y[0] <= y[1] >= y[2].
+MEDIA_EXPORT void QuadraticInterpolation(const float* y_values,
+                                         float* extremum,
+                                         float* extremum_value);
 
 // Search a subset of all candid blocks. The search is performed every
 // |decimation| frames. This reduces complexity by a factor of about
 // 1 / |decimation|. A cubic interpolation is used to have a better estimate of
 // the best match.
 MEDIA_EXPORT int DecimatedSearch(int decimation,
                                  Interval exclude_interval,
                                  const AudioBus* target_block,
                                  const AudioBus* search_segment,
                                  const float* energy_target_block,
@@ skipping 20 matching lines @@
 
 // Return a "periodic" Hann window. This is the first L samples of an L+1
 // Hann window. It is perfect reconstruction for overlap-and-add.
 MEDIA_EXPORT void GetSymmetricHanningWindow(int window_length, float* window);
 
 }  // namespace internal
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_WSOLA_INTERNALS_H_