ComfortNoise: Calculate used scale factor in Q13

webrtc/modules/audio_coding/codecs/cng/webrtc_cng.cc

 /*
  *  Copyright (c) 2012 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/codecs/cng/webrtc_cng.h"
 
 #include <algorithm>
 
+#include "webrtc/base/safe_conversions.h"
 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
 
 namespace webrtc {
 
 namespace {
 
 const size_t kCngMaxOutsizeOrder = 640;
 
 // TODO(ossu): Rename the left-over WebRtcCng according to style guide.
 void WebRtcCng_K2a16(int16_t* k, int useOrder, int16_t* a);
@@ skipping 86 matching lines @@
 
 bool ComfortNoiseDecoder::Generate(rtc::ArrayView<int16_t> out_data,
                                    bool new_period) {
   int16_t excitation[kCngMaxOutsizeOrder];
   int16_t low[kCngMaxOutsizeOrder];
   int16_t lpPoly[WEBRTC_CNG_MAX_LPC_ORDER + 1];
   int16_t ReflBetaStd = 26214;  /* 0.8 in q15. */
   int16_t ReflBetaCompStd = 6553;  /* 0.2 in q15. */
   int16_t ReflBetaNewP = 19661;  /* 0.6 in q15. */
   int16_t ReflBetaCompNewP = 13107;  /* 0.4 in q15. */
-  int16_t Beta, BetaC, tmp1, tmp2, tmp3;
+  int16_t Beta, BetaC;  /* These are in Q15. */
   int32_t targetEnergy;
   int16_t En;
   int16_t temp16;
   const size_t num_samples = out_data.size();
 
   if (num_samples > kCngMaxOutsizeOrder) {
     return false;
   }
 
   if (new_period) {
     dec_used_scale_factor_ = dec_target_scale_factor_;
     Beta = ReflBetaNewP;
     BetaC = ReflBetaCompNewP;
   } else {
     Beta = ReflBetaStd;
     BetaC = ReflBetaCompStd;
   }
 
-  /* Here we use a 0.5 weighting, should possibly be modified to 0.6. */
-  tmp1 = dec_used_scale_factor_ << 2; /* Q13->Q15 */
-  tmp2 = dec_target_scale_factor_ << 2; /* Q13->Q15 */
-  tmp3 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp1, Beta, 15);
-  tmp3 += (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp2, BetaC, 15);
-  dec_used_scale_factor_ = tmp3 >> 2; /* Q15->Q13 */
+  /* Calculate new scale factor in Q13 */
+  dec_used_scale_factor_ =
+      rtc::checked_cast<int16_t>(
+          WEBRTC_SPL_MUL_16_16_RSFT(dec_used_scale_factor_, Beta >> 2, 13) +
+          WEBRTC_SPL_MUL_16_16_RSFT(dec_target_scale_factor_, BetaC >> 2, 13));
 
   dec_used_energy_  = dec_used_energy_ >> 1;
   dec_used_energy_ += dec_target_energy_ >> 1;
 
-  /* Do the same for the reflection coeffs. */
+  /* Do the same for the reflection coeffs, albeit in Q15. */
   for (size_t i = 0; i < WEBRTC_CNG_MAX_LPC_ORDER; i++) {
     dec_used_reflCoefs_[i] = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
         dec_used_reflCoefs_[i], Beta, 15);
     dec_used_reflCoefs_[i] += (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(
         dec_target_reflCoefs_[i], BetaC, 15);
   }
 
   /* Compute the polynomial coefficients. */
   WebRtcCng_K2a16(dec_used_reflCoefs_, WEBRTC_CNG_MAX_LPC_ORDER, lpPoly);
 
@@ skipping 272 matching lines @@
     anyptr = any;
     for (i = 0; i < (m + 2); i++) {
       *aptr++ = *anyptr++;
     }
   }
 }
 
 }  // namespace
 
 }  // namespace webrtc