Avoiding overflow in cross correlation in NetEq.

webrtc/modules/audio_coding/neteq/cross_correlation.h

Index: webrtc/modules/audio_coding/neteq/cross_correlation.h
diff --git a/webrtc/modules/audio_coding/neteq/cross_correlation.h b/webrtc/modules/audio_coding/neteq/cross_correlation.h
new file mode 100644
index 0000000000000000000000000000000000000000..db14141027cd050776a521ee893f3cdfdd39c037
--- /dev/null
+++ b/webrtc/modules/audio_coding/neteq/cross_correlation.h
@@ -0,0 +1,50 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_CODING_NETEQ_CROSS_CORRELATION_H_
+#define WEBRTC_MODULES_AUDIO_CODING_NETEQ_CROSS_CORRELATION_H_
+
+#include "webrtc/common_types.h"
+
+namespace webrtc {
+
+// The function calculates the cross-correlation between two sequences
+// |sequence_1| and |sequence_2|. |sequence_1| is taken as reference, with
+// |sequence_1_length| as its length. |sequence_2| slides for the calculation of
+// cross-correlation. The result will be saved in |cross_correlation|.
+// |cross_correlation_length| correlation points are calculated.
+// The corresponding lag starts from 0, and increases with a step of
+// |cross_correlation_step|. The result is without normalization. To avoid
+// overflow, the result will be right shifted. The amount of shifts will be
+// returned.
+//
+// Input:
+//     - sequence_1     : First sequence (reference).
+//     - sequence_2     : Second sequence (sliding during calculation).
+//     - sequence_1_length : Length of |sequence_1|.
+//     - cross_correlation_length : Number of cross-correlations to calculate.
+//     - cross_correlation_step : Step in the lag for the cross-correlation.
+//
+// Output:
+//      - cross_correlation : The cross-correlation in Q(-right_shifts)
+//
+// Return:
+//      Number of right shifts in cross_correlation.
+
+int CrossCorrelationWithAutoShift(const int16_t* sequence_1,
+                                  const int16_t* sequence_2,
+                                  size_t sequence_1_length,
+                                  size_t cross_correlation_length,
+                                  int cross_correlation_step,
+                                  int32_t* cross_correlation);
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_CROSS_CORRELATION_H_