Fix division by zero errors in IntelligibilityEnhancer

webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.cc

 /*
  *  Copyright (c) 2014 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.
  */
 
 //
 //  Implements core class for intelligibility enhancer.
 //
 //  Details of the model and algorithm can be found in the original paper:
 //  http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6882788
 //
 
 #include "webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h"
 
 #include <math.h>
 #include <stdlib.h>
 #include <algorithm>
+#include <limits>
 #include <numeric>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/common_audio/include/audio_util.h"
 #include "webrtc/common_audio/window_generator.h"
 
 namespace webrtc {
 
 namespace {
 
@@ skipping 184 matching lines @@
     UpdateErbGains();
   }  // Else experiencing variance underflow, so do nothing.
 }
 
 void IntelligibilityEnhancer::SolveForLambda(float power_target,
                                              float power_bot,
                                              float power_top) {
   const float kConvergeThresh = 0.001f;  // TODO(ekmeyerson): Find best values
   const int kMaxIters = 100;             // for these, based on experiments.
 
-  const float reciprocal_power_target = 1.f / power_target;
+  const float reciprocal_power_target =
+      1.f / (power_target + std::numeric_limits<float>::epsilon());
   float lambda_bot = kLambdaBot;
   float lambda_top = kLambdaTop;
   float power_ratio = 2.0f;  // Ratio of achieved power to target power.
   int iters = 0;
   while (std::fabs(power_ratio - 1.0f) > kConvergeThresh &&
          iters <= kMaxIters) {
     const float lambda = lambda_bot + (lambda_top - lambda_bot) / 2.0f;
     SolveForGainsGivenLambda(lambda, start_freq_, gains_eq_.get());
     const float power =
         DotProduct(gains_eq_.get(), filtered_clear_var_.get(), bank_size_);
@@ skipping 61 matching lines @@
         center_freqs_[min(bank_size_, i + rf) - 1] * num_freqs /
             (0.5f * sample_rate_hz_)));
     rr = static_cast<size_t>(round(
         center_freqs_[min(bank_size_, i + 1) - 1] * num_freqs /
             (0.5f * sample_rate_hz_)));
     rrr = min(num_freqs, max(rrr, kOne)) - 1;
     rr = min(num_freqs, max(rr, kOne)) - 1;
 
     float step, element;
 
-    step = 1.0f / (ll - lll);
+    step = ll == lll ? 0.f : 1.f / (ll - lll);
     element = 0.0f;
     for (size_t j = lll; j <= ll; ++j) {
       filter_bank[i - 1][j] = element;
       element += step;
     }
-    step = 1.0f / (rrr - rr);
+    step = rr == rrr ? 0.f : 1.f / (rrr - rr);
     element = 1.0f;
     for (size_t j = rr; j <= rrr; ++j) {
       filter_bank[i - 1][j] = element;
       element -= step;
     }
     for (size_t j = ll; j <= rr; ++j) {
       filter_bank[i - 1][j] = 1.0f;
     }
   }
 
@@ skipping 23 matching lines @@
 
   // Analytic solution for optimal gains. See paper for derivation.
   for (size_t n = start_freq - 1; n < bank_size_; ++n) {
     float alpha0, beta0, gamma0;
     gamma0 = 0.5f * rho_[n] * var_x0[n] * var_n0[n] +
              lambda * var_x0[n] * var_n0[n] * var_n0[n];
     beta0 = lambda * var_x0[n] * (2 - rho_[n]) * var_x0[n] * var_n0[n];
     if (quadratic) {
       alpha0 = lambda * var_x0[n] * (1 - rho_[n]) * var_x0[n] * var_x0[n];
       sols[n] =
-          (-beta0 - sqrtf(beta0 * beta0 - 4 * alpha0 * gamma0)) / (2 * alpha0);
+          (-beta0 - sqrtf(beta0 * beta0 - 4 * alpha0 * gamma0)) /
+          (2 * alpha0 + std::numeric_limits<float>::epsilon());
     } else {
       sols[n] = -gamma0 / beta0;
     }
     sols[n] = fmax(0, sols[n]);
   }
 }
 
 bool IntelligibilityEnhancer::active() const {
   return active_;
 }
 
 }  // namespace webrtc