assimp.assimp/code/StreamWriter.h

/*
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Open Asset Import Library (assimp)
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Copyright (c) 2006-2012, assimp team

All rights reserved.

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  following disclaimer.

* Redistributions in binary form must reproduce the above
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  derived from this software without specific prior
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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*/

/** @file Defines the StreamWriter class which writes data to
 *  a binary stream with a well-defined endianess. */

#ifndef AI_STREAMWRITER_H_INCLUDED
#define AI_STREAMWRITER_H_INCLUDED

#include "ByteSwap.h"

namespace Assimp {

// --------------------------------------------------------------------------------------------
/** Wrapper class around IOStream to allow for consistent writing of binary data in both 
 *  little and big endian format. Don't attempt to instance the template directly. Use 
 *  StreamWriterLE to read from a little-endian stream and StreamWriterBE to read from a 
 *  BE stream. Alternatively, there is StreamWriterAny if the endianess of the output
 *  stream is to be determined at runtime.
 */
// --------------------------------------------------------------------------------------------
template <bool SwapEndianess = false, bool RuntimeSwitch = false>
class StreamWriter
{
	enum {
		INITIAL_CAPACITY = 1024
	};

public:

	// ---------------------------------------------------------------------
	/** Construction from a given stream with a well-defined endianess.
	 * 
	 *  The StreamReader holds a permanent strong reference to the
	 *  stream, which is released upon destruction.
	 *  @param stream Input stream. The stream is not re-seeked and writing
	      continues at the current position of the stream cursor.
	 *  @param le If @c RuntimeSwitch is true: specifies whether the
	 *    stream is in little endian byte order. Otherwise the
	 *    endianess information is defined by the @c SwapEndianess
	 *    template parameter and this parameter is meaningless.  */
	StreamWriter(boost::shared_ptr<IOStream> stream, bool le = false)
		: stream(stream)
		, le(le)
		, cursor()
	{
		ai_assert(stream); 
		buffer.reserve(INITIAL_CAPACITY);
	}

	// ---------------------------------------------------------------------
	StreamWriter(IOStream* stream, bool le = false)
		: stream(boost::shared_ptr<IOStream>(stream))
		, le(le)
		, cursor()
	{
		ai_assert(stream);
		buffer.reserve(INITIAL_CAPACITY);
	}

	// ---------------------------------------------------------------------
	~StreamWriter() {
		stream->Write(&buffer[0], 1, buffer.size());
		stream->Flush();
	}

public:

	// ---------------------------------------------------------------------
	/** Write a float to the stream  */
	void PutF4(float f)
	{
		Put(f);
	}

	// ---------------------------------------------------------------------
	/** Write a double to the stream  */
	void PutF8(double d)	{
		Put(d);
	}

	// ---------------------------------------------------------------------
	/** Write a signed 16 bit integer to the stream */
	void PutI2(int16_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write a signed 8 bit integer to the stream */
	void PutI1(int8_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write an signed 32 bit integer to the stream */
	void PutI4(int32_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write a signed 64 bit integer to the stream */
	void PutI8(int64_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write a unsigned 16 bit integer to the stream */
	void PutU2(uint16_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write a unsigned 8 bit integer to the stream */
	void PutU1(uint8_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write an unsigned 32 bit integer to the stream */
	void PutU4(uint32_t n)	{
		Put(n);
	}

	// ---------------------------------------------------------------------
	/** Write a unsigned 64 bit integer to the stream */
	void PutU8(uint64_t n)	{
		Put(n);
	}

public:

	// ---------------------------------------------------------------------
	/** overload operator<< and allow chaining of MM ops. */
	template <typename T>
	StreamWriter& operator << (T f) {
		Put(f); 
		return *this;
	}

	// ---------------------------------------------------------------------
	std::size_t GetCurrentPos() const {
		return cursor;
	}

	// ---------------------------------------------------------------------
	void SetCurrentPos(std::size_t new_cursor) {
		cursor = new_cursor;
	}

private:

	// ---------------------------------------------------------------------
	/** Generic write method. ByteSwap::Swap(T*) *must* be defined */
	template <typename T>
	void Put(T f)	{
		Intern :: Getter<SwapEndianess,T,RuntimeSwitch>() (&f, le);
		
		if (cursor + sizeof(T) >= buffer.size()) {
			buffer.resize(cursor + sizeof(T));
		}

		void* dest = &buffer[cursor];

		// reinterpret_cast + assignment breaks strict aliasing rules
		// and generally causes trouble on platforms such as ARM that
		// do not silently ignore alignment faults.
		::memcpy(dest, &f, sizeof(T));
		cursor += sizeof(T);
	}

private:

	boost::shared_ptr<IOStream> stream;
	bool le;

	std::vector<uint8_t> buffer;
	std::size_t cursor;
};


// --------------------------------------------------------------------------------------------
// `static` StreamWriter. Their byte order is fixed and they might be a little bit faster.
#ifdef AI_BUILD_BIG_ENDIAN
	typedef StreamWriter<true>  StreamWriterLE;
	typedef StreamWriter<false> StreamWriterBE;
#else
	typedef StreamWriter<true>  StreamWriterBE;
	typedef StreamWriter<false> StreamWriterLE;
#endif

// `dynamic` StreamWriter. The byte order of the input data is specified in the
// c'tor. This involves runtime branching and might be a little bit slower.
typedef StreamWriter<true,true> StreamWriterAny;

} // end namespace Assimp

#endif // !! AI_STREAMWriter_H_INCLUDED