Adds AudioFifo class to Chrome media.

media/base/audio_fifo.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/base/audio_fifo.h"
+
+#include "media/audio/audio_parameters.h"
+#include "base/logging.h"
+
+namespace media {
+
+static void GetSizes(
+    int pos, int max_size, int src_size, int* size, int* wrap_size) {
+  if (pos + src_size > max_size) {
+    // Wrapping is required => derive size of each segment.
+    *size = max_size - pos;
+    *wrap_size = src_size - *size;
+  } else {
+    // Wrapping is not required.
+    *size = src_size;
+    *wrap_size = 0;
+  }
+}
+
+static int UpdatePos(int pos, int step, int max_size) {
+  return ((pos + step) % max_size);
+}
+
+AudioFifo::AudioFifo(int channels, int frames)
+    : audio_bus_(AudioBus::Create(channels, frames)),
+      max_frames_in_fifo_(frames),
+      frames_in_fifo_(0),
+      read_pos_(0),
+      write_pos_(0) {}
+
+AudioFifo::~AudioFifo() {}
+
+bool AudioFifo::Push(const AudioBus* source) {
+  DCHECK(source);
+  DCHECK_EQ(source->channels(), audio_bus_->channels());
+
+  // Ensure that there is space for the new data in the FIFO.
+  const int source_size = source->frames();
+  if (frames_in_fifo_ + source_size > max_frames()) {
+    DLOG(ERROR) << "FIFO overflow.";
+    return false;
+  }
+
+  // Figure out if wrapping is needed and if so what segment sizes we need
+  // when adding the new audio bus content to the FIFO.
+  int append_size = 0;
+  int wrap_size = 0;
+  GetSizes(write_pos_, max_frames(), source_size, &append_size, &wrap_size);
+
+  // Copy all channels from the source to the FIFO. Wrap around if needed.
+  for (int ch = 0; ch < source->channels(); ++ch) {
+    float* dest = audio_bus_->channel(ch);
+    const float* src = source->channel(ch);
+
+    // Append part of (or the complete) source to the FIFO.
+    memcpy(&dest[write_pos_], &src[0], append_size * sizeof(src[0]));
+    if (wrap_size > 0) {
+      // Wrapping is needed: copy remaining part from the source to the FIFO.
+      memcpy(&dest[0], &src[append_size], wrap_size * sizeof(src[0]));
+    }
+  }
+
+  frames_in_fifo_ += source_size;
+  DCHECK_LE(frames_in_fifo_, max_frames());
+  write_pos_ = UpdatePos(write_pos_, source_size, max_frames());
+  return true;
+}
+
+bool AudioFifo::Consume(AudioBus* destination) {
+  DCHECK(destination);
+  DCHECK_EQ(destination->channels(), audio_bus_->channels());
+
+  // It is not possible to ask for more data than what is available in the FIFO.
+  const int dest_size = destination->frames();
+  if (dest_size > frames_in_fifo_) {
+    DLOG(ERROR) << "FIFO underrun.";
+    return false;
+  }
+
+  // Figure out if wrapping is needed and if so what segment sizes we need
+  // when removing audio bus content from the FIFO.
+  int remove_size = 0;
+  int wrap_size = 0;
+  GetSizes(read_pos_, max_frames(), dest_size, &remove_size, &wrap_size);
+
+  // For all channels, remove the requested amount of data from the FIFO
+  // and copy the content to the destination. Wrap around if needed.
+  for (int ch = 0; ch < destination->channels(); ++ch) {
+    float* dest = destination->channel(ch);
+    const float* src = audio_bus_->channel(ch);
+
+    // Append part of (or the complete) source to the destination.
+    memcpy(&dest[0], &src[read_pos_], remove_size * sizeof(src[0]));
+    if (wrap_size > 0) {
+      // Wrapping is needed: copy remaining part to the destination.
+      memcpy(&dest[wrap_size], &src[0], wrap_size * sizeof(src[0]));
+    }
+  }
+
+  frames_in_fifo_ -= dest_size;
+  read_pos_ = UpdatePos(read_pos_, dest_size, max_frames());
+  return true;
+}
+
+void AudioFifo::Clear() {
+  frames_in_fifo_ = 0;
+  read_pos_ = 0;
+  write_pos_ = 0;
+}
+
+}  // namespace media