commit 5d13d6119391e538eb42168058262407054feb15
author Alessio Bazzica <alessiob@webrtc.org> Wed Oct 21 11:30:55 2020
committer Commit Bot <commit-bot@chromium.org> Wed Oct 21 12:58:05 2020
tree 7c73953d8307fdb8623aef5120aa59825fc4849d
parent 7481ba01d1b2778b5370ce820bce0efb944058f5

RNN VAD: LP residual optimized (part 1)

Use hard-coded constants previously computed at runtime within a loop in
`ComputeAndPostProcessLpcCoefficients`.

Note that the `RnnVadTest.LpResidualPipelineBitExactness` unit test
is still passing.

Bug: webrtc:10480
Change-Id: Iaec178c56937449c3fe9af881354d19cc8c47c7d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/189961
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32462}

modules/audio_processing/agc2/rnn_vad/lp_residual.cc

diff --git a/modules/audio_processing/agc2/rnn_vad/lp_residual.cc b/modules/audio_processing/agc2/rnn_vad/lp_residual.cc
index 1a124a3..dabe507 100644
--- a/modules/audio_processing/agc2/rnn_vad/lp_residual.cc
+++ b/modules/audio_processing/agc2/rnn_vad/lp_residual.cc
@@ -101,17 +101,17 @@
   ComputeInitialInverseFilterCoefficients(auto_corr, lpc_coeffs_pre);
   // LPC coefficients post-processing.
   // TODO(bugs.webrtc.org/9076): Consider removing these steps.
-  float c1 = 1.f;
-  for (size_t i = 0; i < kNumLpcCoefficients - 1; ++i) {
-    c1 *= 0.9f;
-    lpc_coeffs_pre[i] *= c1;
-  }
-  const float c2 = 0.8f;
-  lpc_coeffs[0] = lpc_coeffs_pre[0] + c2;
-  lpc_coeffs[1] = lpc_coeffs_pre[1] + c2 * lpc_coeffs_pre[0];
-  lpc_coeffs[2] = lpc_coeffs_pre[2] + c2 * lpc_coeffs_pre[1];
-  lpc_coeffs[3] = lpc_coeffs_pre[3] + c2 * lpc_coeffs_pre[2];
-  lpc_coeffs[4] = c2 * lpc_coeffs_pre[3];
+  lpc_coeffs_pre[0] *= 0.9f;
+  lpc_coeffs_pre[1] *= 0.9f * 0.9f;
+  lpc_coeffs_pre[2] *= 0.9f * 0.9f * 0.9f;
+  lpc_coeffs_pre[3] *= 0.9f * 0.9f * 0.9f * 0.9f;
+  constexpr float kC = 0.8f;
+  lpc_coeffs[0] = lpc_coeffs_pre[0] + kC;
+  lpc_coeffs[1] = lpc_coeffs_pre[1] + kC * lpc_coeffs_pre[0];
+  lpc_coeffs[2] = lpc_coeffs_pre[2] + kC * lpc_coeffs_pre[1];
+  lpc_coeffs[3] = lpc_coeffs_pre[3] + kC * lpc_coeffs_pre[2];
+  lpc_coeffs[4] = kC * lpc_coeffs_pre[3];
+  static_assert(kNumLpcCoefficients == 5, "Update `lpc_coeffs(_pre)`.");
 }
 
 void ComputeLpResidual(