libraries/lib-utility/memorystream.cpp

Go to the documentation of this file.

/**********************************************************************
 
  Audacity: A Digital Audio Editor
 
  MemoryStream.cpp
 
  Dmitry Vedenko
 
**********************************************************************/
 
#include "MemoryStream.h"
 
#include <algorithm>
 
void MemoryStream::Clear()
{
   mChunks = {};
   mLinearData = {};
   mDataSize = 0;
}
 
void MemoryStream::AppendByte(char data)
{
   AppendData(&data, 1);
}
 
void MemoryStream::AppendData(const void* data, const size_t length)
{
   if (mChunks.empty())
      mChunks.emplace_back();
 
   StreamChunk dataView = { data, length };
 
   while (mChunks.back().Append(dataView) > 0)
      mChunks.emplace_back();
 
   mDataSize += length;
}
 
const void* MemoryStream::GetData() const
{
   if (!mChunks.empty())
   {
      const size_t desiredSize = GetSize();
 
      mLinearData.reserve(desiredSize);
 
      for (const Chunk& chunk : mChunks)
      {
         auto begin = chunk.Data.begin();
         auto end = begin + chunk.BytesUsed;
 
         mLinearData.insert(mLinearData.end(), begin, end);
      }
 
      mChunks = {};
   }
 
   return mLinearData.data();
}
 
const size_t MemoryStream::GetSize() const noexcept
{
   return mDataSize;
}
 
size_t MemoryStream::Chunk::Append(StreamChunk& dataView)
{
   const size_t dataSize = dataView.second;
 
   const size_t bytesToWrite = std::min(ChunkSize - BytesUsed, dataSize);
   const size_t bytesLeft = dataSize - bytesToWrite;
 
   const uint8_t* beginData = static_cast<const uint8_t*>(dataView.first);
   const uint8_t* endData = beginData + bytesToWrite;
 
   // Some extreme micro optimization for MSVC (at least)
   // std::copy will generate a call to memmove in any case
   // which will be slower than just writing the byte
   if (bytesToWrite == 1)
   {
      Data[BytesUsed] = *beginData;
   }
   else
   {
      // There is a chance for unaligned access, so we do no handle
      // types as int32_t separately. Unaligned access is slow on x86
      // and fails horribly on ARM
      std::copy(beginData, endData, Data.begin() + BytesUsed);
   }
 
   dataView.first = endData;
   dataView.second = bytesLeft;
 
   BytesUsed += bytesToWrite;
 
   return bytesLeft;
}
 
bool MemoryStream::IsEmpty() const noexcept
{
   return mDataSize == 0;
}
 
MemoryStream::Iterator MemoryStream::begin() const
{
   return Iterator(this, true);
}
 
MemoryStream::Iterator MemoryStream::end() const
{
   return Iterator(this, false);
}
 
MemoryStream::Iterator::Iterator(const MemoryStream* stream, bool isBegin)
    : mStream(stream)
    , mListIterator(isBegin ? mStream->mChunks.cbegin() : mStream->mChunks.cend())
    , mShowLinearPart(isBegin && mStream->mLinearData.size() > 0)
{
}
 
MemoryStream::Iterator& MemoryStream::Iterator::operator++()
{
   if (mShowLinearPart)
      mShowLinearPart = false;
   else
      ++mListIterator;
 
   return *this;
}
 
MemoryStream::Iterator MemoryStream::Iterator::operator++(int)
{
   Iterator result { *this };
   this->operator++();
   return result;
}
 
MemoryStream::StreamChunk MemoryStream::Iterator::operator*() const
{
   if (mShowLinearPart)
      return { mStream->mLinearData.data(), mStream->mLinearData.size() };
 
   return { mListIterator->Data.data(), mListIterator->BytesUsed };
}
 
MemoryStream::StreamChunk MemoryStream::Iterator::operator->() const
{
   return this->operator*();
}
 
bool MemoryStream::Iterator::operator!=(const Iterator& rhs) const noexcept
{
   return !(*this == rhs);
}
 
bool MemoryStream::Iterator::operator==(const Iterator& rhs) const noexcept
{
   return mStream == rhs.mStream && mListIterator == rhs.mListIterator &&
          mShowLinearPart == rhs.mShowLinearPart;
}