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#include "internal.h"
CRingBuffer::CRingBuffer(
VOID
) : m_Size(0),
m_Base(NULL),
m_End(NULL),
m_Head(NULL),
m_Tail(NULL)
{
return;
}
CRingBuffer::~CRingBuffer(
VOID
)
{
if (m_Base)
{
delete[] m_Base;
}
}
HRESULT
CRingBuffer::Initialize(
_In_ SIZE_T BufferSize
)
{
HRESULT hr = S_OK;
PBYTE buffer = NULL;
if (0 == BufferSize)
{
hr = E_INVALIDARG;
}
//
// Allocate the buffer.
//
if (SUCCEEDED(hr))
{
buffer = new BYTE[BufferSize];
if (buffer == NULL)
{
hr = E_OUTOFMEMORY;
}
}
//
// Initialize the ring buffer pointers.
//
if (SUCCEEDED(hr))
{
m_Size = BufferSize;
m_Base = buffer;
m_End = buffer + BufferSize;
m_Head = buffer;
m_Tail = buffer;
}
if (FAILED(hr))
{
if (buffer)
{
delete[] buffer;
m_Base = NULL;
}
}
return hr;
}
HRESULT
CRingBuffer::Write(
_In_reads_bytes_(DataSize) PBYTE Data,
_In_ SIZE_T DataSize
)
{
SIZE_T availableSpace;
SIZE_T bytesToCopy;
SIZE_T spaceFromCurrToEnd;
WUDF_TEST_DRIVER_ASSERT(Data && (0 != DataSize));
if (m_Tail >= m_End)
{
return E_UNEXPECTED;
}
//
// Get the amount of space available in the buffer
//
GetAvailableSpace(&availableSpace);
//
// If there is not enough space to fit in all the data passed in by the
// caller then copy as much as possible and throw away the rest
//
if (availableSpace < DataSize)
{
bytesToCopy = availableSpace;
}
else
{
bytesToCopy = DataSize;
}
if (bytesToCopy)
{
//
// The buffer has some space at least
//
if ((m_Tail+bytesToCopy) > m_End)
{
//
// The data being written will wrap around the end of the buffer.
// So the copy has to be done in two steps -
// * X bytes from current position to end of the buffer
// * the remaining (bytesToCopy - X) from the start of the buffer
//
//
// The first step of the copy ...
//
spaceFromCurrToEnd = m_End - m_Tail;
CopyMemory(m_Tail, Data, spaceFromCurrToEnd);
Data += spaceFromCurrToEnd;
bytesToCopy -= spaceFromCurrToEnd;
//
// The second step of the copy ...
//
CopyMemory(m_Base, Data, bytesToCopy);
//
// Advance the tail pointer
//
m_Tail = m_Base + bytesToCopy;
}
else
{
//
// Data does NOT wrap around the end of the buffer. Just copy it
// over in a single step
//
CopyMemory(m_Tail, Data, bytesToCopy);
//
// Advance the tail pointer
//
m_Tail += bytesToCopy;
if (m_Tail == m_End)
{
//
// We have exactly reached the end of the buffer. The next
// write should wrap around and start from the beginning.
//
m_Tail = m_Base;
}
}
WUDF_TEST_DRIVER_ASSERT(m_Tail < m_End);
}
return S_OK;
}
HRESULT
CRingBuffer::Read(
_Out_writes_bytes_to_(DataSize, *BytesCopied) PBYTE Data,
_In_ SIZE_T DataSize,
_Out_ SIZE_T *BytesCopied
)
{
SIZE_T availableData;
SIZE_T dataFromCurrToEnd;
WUDF_TEST_DRIVER_ASSERT(Data && (DataSize != 0));
if (m_Head >= m_End)
{
return E_UNEXPECTED;
}
//
// Get the amount of data available in the buffer
//
GetAvailableData(&availableData);
if (availableData == 0)
{
*BytesCopied = 0;
return S_OK;
}
if (DataSize > availableData)
{
DataSize = availableData;
}
*BytesCopied = DataSize;
if ((m_Head + DataSize) > m_End)
{
//
// The data requested by the caller is wrapped around the end of the
// buffer. So we'll do the copy in two steps -
// * Copy X bytes from the current position to the end buffer into
// the caller's buffer
// * Copy (DataSize - X) bytes from the beginning to the buffer into
// the caller's buffer
//
//
// The first step of the copy ...
//
dataFromCurrToEnd = m_End - m_Head;
CopyMemory(Data, m_Head, dataFromCurrToEnd);
Data += dataFromCurrToEnd;
DataSize -= dataFromCurrToEnd;
//
// The second step of the copy ...
//
CopyMemory(Data, m_Base, DataSize);
//
// Advance the head pointer
//
m_Head = m_Base + DataSize;
}
else
{
//
// The data in the buffer is NOT wrapped around the end of the buffer.
// Simply copy the data over to the caller's buffer in a single step.
//
CopyMemory(Data, m_Head, DataSize);
//
// Advance the head pointer
//
m_Head += DataSize;
if (m_Head == m_End)
{
//
// We have exactly reached the end of the buffer. The next
// read should wrap around and start from the beginning.
//
m_Head = m_Base;
}
}
WUDF_TEST_DRIVER_ASSERT(m_Head < m_End);
return S_OK;
}
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