dom/media/AudioCompactor.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6 #include "AudioCompactor.h"
   7 #if defined(MOZ_MEMORY)
   8 #  include "mozmemory.h"
   9 #endif
  10
  11 namespace mozilla {
  12
  13 static size_t MallocGoodSize(size_t aSize) {
  14 #if defined(MOZ_MEMORY)
  15   return malloc_good_size(aSize);
  16 #else
  17   return aSize;
  18 #endif
  19 }
  20
  21 static size_t TooMuchSlop(size_t aSize, size_t aAllocSize, size_t aMaxSlop) {
  22   // If the allocated size is less then our target size, then we
  23   // are chunking.  This means it will be completely filled with
  24   // zero slop.
  25   size_t slop = (aAllocSize > aSize) ? (aAllocSize - aSize) : 0;
  26   return slop > aMaxSlop;
  27 }
  28
  29 uint32_t AudioCompactor::GetChunkSamples(uint32_t aFrames, uint32_t aChannels,
  30                                          size_t aMaxSlop) {
  31   size_t size = AudioDataSize(aFrames, aChannels);
  32   size_t chunkSize = MallocGoodSize(size);
  33
  34   // Reduce the chunk size until we meet our slop goal or the chunk
  35   // approaches an unreasonably small size.
  36   while (chunkSize > 64 && TooMuchSlop(size, chunkSize, aMaxSlop)) {
  37     chunkSize = MallocGoodSize(chunkSize / 2);
  38   }
  39
  40   // Calculate the number of samples based on expected malloc size
  41   // in order to allow as many frames as possible to be packed.
  42   return chunkSize / sizeof(AudioDataValue);
  43 }
  44
  45 uint32_t AudioCompactor::NativeCopy::operator()(AudioDataValue* aBuffer,
  46                                                 uint32_t aSamples) {
  47   NS_ASSERTION(aBuffer, "cannot copy to null buffer pointer");
  48   NS_ASSERTION(aSamples, "cannot copy zero values");
  49
  50   size_t bufferBytes = aSamples * sizeof(AudioDataValue);
  51   size_t maxBytes = std::min(bufferBytes, mSourceBytes - mNextByte);
  52   uint32_t frames = maxBytes / BytesPerFrame(mChannels);
  53   size_t bytes = frames * BytesPerFrame(mChannels);
  54
  55   NS_ASSERTION((mNextByte + bytes) <= mSourceBytes,
  56                "tried to copy beyond source buffer");
  57   NS_ASSERTION(bytes <= bufferBytes, "tried to copy beyond destination buffer");
  58
  59   memcpy(aBuffer, mSource + mNextByte, bytes);
  60
  61   mNextByte += bytes;
  62   return frames;
  63 }
  64
  65 }  // namespace mozilla