Index: webrtc/modules/audio_coding/neteq/cross_correlation.cc |
diff --git a/webrtc/modules/audio_coding/neteq/cross_correlation.cc b/webrtc/modules/audio_coding/neteq/cross_correlation.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..ad89ab8a139eafadafb27632de5e9bc3ddbc5376 |
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+++ b/webrtc/modules/audio_coding/neteq/cross_correlation.cc |
@@ -0,0 +1,62 @@ |
+/* |
+ * 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. |
+ */ |
+ |
+#include "webrtc/modules/audio_coding/neteq/cross_correlation.h" |
+ |
+#include <cstdlib> |
+#include <limits> |
+ |
+#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h" |
+ |
+namespace webrtc { |
+ |
+// This function decides the overflow-protecting scaling and calls |
+// WebRtcSpl_CrossCorrelation. |
+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) { |
+ // Find the maximum absolute value of sequence_1 and 2. |
+ const int16_t max_1 = WebRtcSpl_MaxAbsValueW16(sequence_1, sequence_1_length); |
+ const int sequence_2_shift = |
+ cross_correlation_step * (static_cast<int>(cross_correlation_length) - 1); |
+ const int16_t* sequence_2_start = |
+ sequence_2_shift >= 0 ? sequence_2 : sequence_2 + sequence_2_shift; |
+ const size_t sequence_2_length = |
+ sequence_1_length + std::abs(sequence_2_shift); |
+ const int16_t max_2 = |
+ WebRtcSpl_MaxAbsValueW16(sequence_2_start, sequence_2_length); |
+ |
+ // In order to avoid overflow when computing the sum we should scale the |
+ // samples so that (in_vector_length * max_1 * max_2) will not overflow. |
+ // Expected scaling fulfills |
+ // 1) sufficient: |
+ // sequence_1_length * (max_1 * max_2 >> scaling) <= 0x7fffffff; |
+ // 2) necessary: |
+ // if (scaling > 0) |
+ // sequence_1_length * (max_1 * max_2 >> (scaling - 1)) > 0x7fffffff; |
+ // The following calculation fulfills 1) and almost fulfills 2). |
+ // There are some corner cases that 2) is not satisfied, e.g., |
+ // max_1 = 17, max_2 = 30848, sequence_1_length = 4095, in such case, |
+ // optimal scaling is 0, while the following calculation results in 1. |
+ const int32_t factor = (max_1 * max_2) / (std::numeric_limits<int32_t>::max() |
+ / static_cast<int32_t>(sequence_1_length)); |
+ const int scaling = factor == 0 ? 0 : 31 - WebRtcSpl_NormW32(factor); |
+ |
+ WebRtcSpl_CrossCorrelation(cross_correlation, sequence_1, sequence_2, |
+ sequence_1_length, cross_correlation_length, |
+ scaling, cross_correlation_step); |
+ |
+ return scaling; |
+} |
+ |
+} // namespace webrtc |