Avoiding overflow in cross correlation in NetEq.

webrtc/modules/audio_coding/neteq/expand.cc

Index: webrtc/modules/audio_coding/neteq/expand.cc
diff --git a/webrtc/modules/audio_coding/neteq/expand.cc b/webrtc/modules/audio_coding/neteq/expand.cc
index ef7af46597e4344156dc48b553d467934622f4b2..9f4404662a96d7f477e6a8ee8faae6eee50ef7f7 100644
--- a/webrtc/modules/audio_coding/neteq/expand.cc
+++ b/webrtc/modules/audio_coding/neteq/expand.cc
@@ -19,6 +19,7 @@
 #include "webrtc/base/safe_conversions.h"
 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
 #include "webrtc/modules/audio_coding/neteq/background_noise.h"
+#include "webrtc/modules/audio_coding/neteq/cross_correlation.h"
 #include "webrtc/modules/audio_coding/neteq/dsp_helper.h"
 #include "webrtc/modules/audio_coding/neteq/random_vector.h"
 #include "webrtc/modules/audio_coding/neteq/statistics_calculator.h"
@@ -379,12 +380,10 @@ void Expand::AnalyzeSignal(int16_t* random_vector) {
   InitializeForAnExpandPeriod();
 
   // Calculate correlation in downsampled domain (4 kHz sample rate).
-  int correlation_scale;
   size_t correlation_length = 51;  // TODO(hlundin): Legacy bit-exactness.
   // If it is decided to break bit-exactness |correlation_length| should be
   // initialized to the return value of Correlation().
-  Correlation(audio_history, signal_length, correlation_vector,
-              &correlation_scale);
+  Correlation(audio_history, signal_length, correlation_vector);
 
   // Find peaks in correlation vector.
   DspHelper::PeakDetection(correlation_vector, correlation_length,
@@ -450,21 +449,13 @@ void Expand::AnalyzeSignal(int16_t* random_vector) {
 
   for (size_t channel_ix = 0; channel_ix < num_channels_; ++channel_ix) {
     ChannelParameters& parameters = channel_parameters_[channel_ix];
-    // Calculate suitable scaling.
-    int16_t signal_max = WebRtcSpl_MaxAbsValueW16(
-        &audio_history[signal_length - correlation_length - start_index
-                       - correlation_lags],
-                       correlation_length + start_index + correlation_lags - 1);
-    correlation_scale = (31 - WebRtcSpl_NormW32(signal_max * signal_max)) +
-        (31 - WebRtcSpl_NormW32(static_cast<int32_t>(correlation_length))) - 31;
-    correlation_scale = std::max(0, correlation_scale);
 
     // Calculate the correlation, store in |correlation_vector2|.
-    WebRtcSpl_CrossCorrelation(
+    int correlation_scale = CrossCorrelationWithAutoShift(
         correlation_vector2,
         &(audio_history[signal_length - correlation_length]),
         &(audio_history[signal_length - correlation_length - start_index]),
-        correlation_length, correlation_lags, correlation_scale, -1);
+        correlation_length, correlation_lags, -1);
 
     // Find maximizing index.
     best_index = WebRtcSpl_MaxIndexW32(correlation_vector2, correlation_lags);
@@ -582,13 +573,6 @@ void Expand::AnalyzeSignal(int16_t* random_vector) {
     }
 
     // Calculate the LPC and the gain of the filters.
-    // Calculate scale value needed for auto-correlation.
-    correlation_scale = WebRtcSpl_MaxAbsValueW16(
-        &(audio_history[signal_length - fs_mult_lpc_analysis_len]),
-        fs_mult_lpc_analysis_len);
-
-    correlation_scale = std::min(16 - WebRtcSpl_NormW32(correlation_scale), 0);
-    correlation_scale = std::max(correlation_scale * 2 + 7, 0);
 
     // Calculate kUnvoicedLpcOrder + 1 lags of the auto-correlation function.
     size_t temp_index = signal_length - fs_mult_lpc_analysis_len -
@@ -601,11 +585,12 @@ void Expand::AnalyzeSignal(int16_t* random_vector) {
     memcpy(&temp_signal[kUnvoicedLpcOrder],
            &audio_history[temp_index + kUnvoicedLpcOrder],
            sizeof(int16_t) * fs_mult_lpc_analysis_len);
-    WebRtcSpl_CrossCorrelation(auto_correlation,
-                               &temp_signal[kUnvoicedLpcOrder],
-                               &temp_signal[kUnvoicedLpcOrder],
-                               fs_mult_lpc_analysis_len, kUnvoicedLpcOrder + 1,
-                               correlation_scale, -1);
+    correlation_scale = CrossCorrelationWithAutoShift(
+        auto_correlation,
+        &temp_signal[kUnvoicedLpcOrder],
+        &temp_signal[kUnvoicedLpcOrder],
+        fs_mult_lpc_analysis_len,
+        kUnvoicedLpcOrder + 1, -1);
     delete [] temp_signal;
 
     // Verify that variance is positive.
@@ -766,8 +751,7 @@ Expand::ChannelParameters::ChannelParameters()
 
 void Expand::Correlation(const int16_t* input,
                          size_t input_length,
-                         int16_t* output,
-                         int* output_scale) const {
+                         int16_t* output) const {
   // Set parameters depending on sample rate.
   const int16_t* filter_coefficients;
   size_t num_coefficients;
@@ -814,13 +798,12 @@ void Expand::Correlation(const int16_t* input,
                               downsampled_input, norm_shift);
 
   int32_t correlation[kNumCorrelationLags];
-  static const int kCorrelationShift = 6;
-  WebRtcSpl_CrossCorrelation(
+  CrossCorrelationWithAutoShift(
       correlation,
       &downsampled_input[kDownsampledLength - kCorrelationLength],
       &downsampled_input[kDownsampledLength - kCorrelationLength
           - kCorrelationStartLag],
-      kCorrelationLength, kNumCorrelationLags, kCorrelationShift, -1);
+      kCorrelationLength, kNumCorrelationLags, -1);
 
   // Normalize and move data from 32-bit to 16-bit vector.
   int32_t max_correlation = WebRtcSpl_MaxAbsValueW32(correlation,
@@ -829,8 +812,6 @@ void Expand::Correlation(const int16_t* input,
       std::max(18 - WebRtcSpl_NormW32(max_correlation), 0));
   WebRtcSpl_VectorBitShiftW32ToW16(output, kNumCorrelationLags, correlation,
                                    norm_shift2);
-  // Total scale factor (right shifts) of correlation value.
-  *output_scale = 2 * norm_shift + kCorrelationShift + norm_shift2;
 }
 
 void Expand::UpdateLagIndex() {