third_party/WebKit/Source/platform/audio/FFTConvolver.cpp

/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 */

#include "platform/audio/FFTConvolver.h"
#include "platform/audio/VectorMath.h"

namespace blink {

using namespace VectorMath;

FFTConvolver::FFTConvolver(size_t fft_size)
    : frame_(fft_size),
      read_write_index_(0),
      input_buffer_(fft_size),  // 2nd half of buffer is always zeroed
      output_buffer_(fft_size),
      last_overlap_buffer_(fft_size / 2) {}

void FFTConvolver::Process(FFTFrame* fft_kernel,
                           const float* source_p,
                           float* dest_p,
                           size_t frames_to_process) {
  size_t half_size = FftSize() / 2;

  // framesToProcess must be an exact multiple of halfSize,
  // or halfSize is a multiple of framesToProcess when halfSize >
  // framesToProcess.
  bool is_good =
      !(half_size % frames_to_process && frames_to_process % half_size);
  DCHECK(is_good);
  if (!is_good)
    return;

  size_t number_of_divisions =
      half_size <= frames_to_process ? (frames_to_process / half_size) : 1;
  size_t division_size =
      number_of_divisions == 1 ? frames_to_process : half_size;

  for (size_t i = 0; i < number_of_divisions;
       ++i, source_p += division_size, dest_p += division_size) {
    // Copy samples to input buffer (note contraint above!)
    float* input_p = input_buffer_.Data();

    // Sanity check
    bool is_copy_good1 =
        source_p && input_p &&
        read_write_index_ + division_size <= input_buffer_.size();
    DCHECK(is_copy_good1);
    if (!is_copy_good1)
      return;

    memcpy(input_p + read_write_index_, source_p,
           sizeof(float) * division_size);

    // Copy samples from output buffer
    float* output_p = output_buffer_.Data();

    // Sanity check
    bool is_copy_good2 =
        dest_p && output_p &&
        read_write_index_ + division_size <= output_buffer_.size();
    DCHECK(is_copy_good2);
    if (!is_copy_good2)
      return;

    memcpy(dest_p, output_p + read_write_index_, sizeof(float) * division_size);
    read_write_index_ += division_size;

    // Check if it's time to perform the next FFT
    if (read_write_index_ == half_size) {
      // The input buffer is now filled (get frequency-domain version)
      frame_.DoFFT(input_buffer_.Data());
      frame_.Multiply(*fft_kernel);
      frame_.DoInverseFFT(output_buffer_.Data());

      // Overlap-add 1st half from previous time
      Vadd(output_buffer_.Data(), 1, last_overlap_buffer_.Data(), 1,
           output_buffer_.Data(), 1, half_size);

      // Finally, save 2nd half of result
      bool is_copy_good3 = output_buffer_.size() == 2 * half_size &&
                           last_overlap_buffer_.size() == half_size;
      DCHECK(is_copy_good3);
      if (!is_copy_good3)
        return;

      memcpy(last_overlap_buffer_.Data(), output_buffer_.Data() + half_size,
             sizeof(float) * half_size);

      // Reset index back to start for next time
      read_write_index_ = 0;
    }
  }
}

void FFTConvolver::Reset() {
  last_overlap_buffer_.Zero();
  read_write_index_ = 0;
}

}  // namespace blink