text: /*
   *  Copyright (c) 2018 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 "modules/audio_processing/agc2/fixed_gain_controller.h"
  
  #include <algorithm>
  #include <cmath>
  
  #include "api/array_view.h"
  #include "common_audio/include/audio_util.h"
  #include "modules/audio_processing/agc2/agc2_common.h"
  #include "modules/audio_processing/agc2/interpolated_gain_curve.h"
  #include "modules/audio_processing/logging/apm_data_dumper.h"
  #include "rtc_base/checks.h"
  #include "rtc_base/logging.h"
  #include "rtc_base/numerics/safe_minmax.h"
  
  namespace webrtc {
  namespace {
  
  // Returns true when the gain factor is so close to 1 that it would
  // not affect int16 samples.
  bool CloseToOne(float gain_factor) {
    return 1.f - 1.f / kMaxFloatS16Value <= gain_factor &&
           gain_factor <= 1.f + 1.f / kMaxFloatS16Value;
  }
  }  // namespace
  
  FixedGainController::FixedGainController(ApmDataDumper* apm_data_dumper)
      : FixedGainController(apm_data_dumper, "Agc2") {}
  
  FixedGainController::FixedGainController(ApmDataDumper* apm_data_dumper,
                                           std::string histogram_name_prefix)
      : apm_data_dumper_(apm_data_dumper),
        gain_curve_applier_(48000, apm_data_dumper_, histogram_name_prefix) {
    // Do update histograms.xml when adding name prefixes.
    RTC_DCHECK(histogram_name_prefix == "" || histogram_name_prefix == "Test" ||
               histogram_name_prefix == "AudioMixer" ||
               histogram_name_prefix == "Agc2");
  }
  
  void FixedGainController::SetGain(float gain_to_apply_db) {
    // Changes in gain_to_apply_ cause discontinuities. We assume
    // gain_to_apply_ is set in the beginning of the call. If it is
    // frequently changed, we should add interpolation between the
    // values.
    // The gain
    RTC_DCHECK_LE(-50.f, gain_to_apply_db);
    RTC_DCHECK_LE(gain_to_apply_db, 50.f);
    const float previous_applied_gained = gain_to_apply_;
    gain_to_apply_ = DbToRatio(gain_to_apply_db);
    RTC_DCHECK_LT(0.f, gain_to_apply_);
    RTC_DLOG(LS_INFO) << "Gain to apply: " << gain_to_apply_db << " db.";
    // Reset the gain curve applier to quickly react on abrupt level changes
    // caused by large changes of the applied gain.
    if (previous_applied_gained != gain_to_apply_) {
      gain_curve_applier_.Reset();
    }
  }
  
  void FixedGainController::SetSampleRate(size_t sample_rate_hz) {
    gain_curve_applier_.SetSampleRate(sample_rate_hz);
  }
  
  void FixedGainController::Process(AudioFrameView<float> signal) {
    // Apply fixed digital gain. One of the
    // planned usages of the FGC is to only use the limiter. In that
    // case, the gain would be 1.0. Not doing the multiplications speeds
    // it up considerably. Hence the check.
    if (!CloseToOne(gain_to_apply_)) {
      for (size_t k = 0; k < signal.num_channels(); ++k) {
        rtc::ArrayView<float> channel_view = signal.channel(k);
        for (auto& sample : channel_view) {
          sample *= gain_to_apply_;
        }
      }
    }
  
    // Use the limiter.
    gain_curve_applier_.Process(signal);
  
    // Dump data for debug.
    const auto channel_view = signal.channel(0);
    apm_data_dumper_->DumpRaw("agc2_fixed_digital_gain_curve_applier",
                              channel_view.size(), channel_view.data());
    // Hard-clipping.
    for (size_t k = 0; k < signal.num_channels(); ++k) {
      rtc::ArrayView<float> channel_view = signal.channel(k);
      for (auto& sample : channel_view) {
        sample = rtc::SafeClamp(sample, kMinFloatS16Value, kMaxFloatS16Value);
      }
    }
  }
  }  // namespace webrtc
  