RaptorQ.hpp

	if (error) {
		p.set_value ({Error::WRONG_INPUT, 0});
		return p.get_future();
	}

	// do not add work to the pool to save up memory.
	// let "add_symbol craete the Decoders as needed.

	// spawn thread waiting for other thread exit.
	// this way we can set_value to the future when needed.
	auto future = p.get_future();
	if (Compute::NONE != (flags & Compute::NO_BACKGROUND)) {
		wait_threads (this, flags, std::move(p));
	} else {
		std::unique_lock<std::mutex> pool_wait_lock (_mtx);
		UNUSED(pool_wait_lock);
		pool_wait.emplace_back(wait_threads, this, flags, std::move(p));
	}
	return future;
}

template <typename In_It, typename Fwd_It>
void Decoder<In_It, Fwd_It>::wait_threads (Decoder<In_It, Fwd_It> *obj,
									const Compute flags,
									std::promise<std::pair<Error, uint8_t>> p)
{
	do {
		if (obj->exiting) {	// make sure we can exit
			p.set_value ({Error::EXITING, 0});
			break;
		}
		// pool is global (static), so wait only for our stuff.
		std::unique_lock<std::mutex> lock (obj->pool_lock->first);
		if (obj->exiting) { // make sure we can exit
			p.set_value ({Error::EXITING, 0});
			break;
		}
		auto status = obj->get_report (flags);
		if (Error::WORKING != status.first) {
			p.set_value (status);
			break;
		}

		obj->pool_lock->second.wait (lock); // conditional wait
		if (obj->exiting) {	// make sure we can exit
			p.set_value ({Error::EXITING, 0});
			break;
		}
		status = obj->get_report (flags);
		lock.unlock();
		if (Error::WORKING != status.first) {
			p.set_value (status);
			break;
		}
	} while (true);

	// delete ourselves from the waiting thread vector.
	std::unique_lock<std::mutex> lock (obj->_mtx);
	UNUSED (lock);
	for (auto it = obj->pool_wait.begin(); it != obj->pool_wait.end(); ++it) {
		if (it->get_id() == std::this_thread::get_id()) {
			it->detach();
			obj->pool_wait.erase (it);
			break;
		}
	}
}

template <typename In_It, typename Fwd_It>
std::pair<Error, uint8_t> Decoder<In_It, Fwd_It>::get_report (
														const Compute flags)
{
	if (Compute::COMPLETE == (flags & Compute::COMPLETE) ||
			Compute::PARTIAL_FROM_BEGINNING ==
									(flags & Compute::PARTIAL_FROM_BEGINNING)) {
		auto it = decoders.begin();
		// get first non-reported block.
		for (;it != decoders.end(); ++it) {
			if (pool_last_reported <= it->first)
				break;
		}
		uint16_t reportable = 0;
		// get last reportable block
		for (; it != decoders.end(); ++it) {
			auto ptr = it->second.dec;
			if (ptr != nullptr && !ptr->ready())
				break;
			++reportable;
		}
		if (reportable > 0) {
			pool_last_reported += reportable;
			if (Compute::PARTIAL_FROM_BEGINNING ==
									(flags & Compute::PARTIAL_FROM_BEGINNING)) {
				return {Error::NONE, pool_last_reported};
			} else {
				// complete
				if (pool_last_reported == _blocks)
					return {Error::NONE, pool_last_reported};
			}
		}
	} else if (Compute::PARTIAL_ANY == (flags & Compute::PARTIAL_ANY)) {
		for (auto &it : decoders) {
			if (!it.second.reported) {
				auto ptr = it.second.dec;
				if (ptr != nullptr && ptr->ready()) {
					return {Error::NONE, it.first};
				}
			}
		}
	}
	// can be reached if computing thread was stopped
	return {Error::WORKING, 0};
}

template <typename In_It, typename Fwd_It>
uint64_t Decoder<In_It, Fwd_It>::decode_bytes (Fwd_It &start, const Fwd_It end,
														const uint8_t skip)
{
	// Decode from the beginning, up untill we can.
	// return number of BYTES written, starting at "start + skip" bytes
	//
	// in case the last iterator is only half written, "start" will
	// point to the half-written iterator.

	uint64_t written = 0;
	uint8_t new_skip = skip;
	for (uint8_t sbn = 0; sbn < blocks(); ++sbn) {
		std::unique_lock<std::mutex> block_lock (_mtx);
		auto it = decoders.find (sbn);
		if (it == decoders.end())
			return written;
		auto dec_ptr = it->second.dec;
		block_lock.unlock();

		if (!dec_ptr->ready()) {
			if (!use_pool && dec_ptr->can_decode()) {
				Work_State state = Work_State::KEEP_WORKING;
				auto ret = dec_ptr->decode (&state);
				if (Impl::Decoder<In_It>::Decoder_Result::DECODED != ret)
					return written;
			} else {
				return written;
			}
		}

		Impl::De_Interleaver<Fwd_It> de_interleaving (dec_ptr->get_symbols(),
													_sub_blocks, _alignment);
		// FIXME FIXME FIXME FIXME FIXME:
		// the size of the user data is *NOT* always aligned with the
		// symbol, and not with the iterator.
		// Therefore we need to limit the amount of written data
		// when writing the last block. limit with data size, not block size.

		uint64_t max_bytes = block_size (sbn);
		if (sbn == (blocks() - 1)) {
			// size of the data (_size) is different from the sum of the size of
			// all blocks. get the real size, so we do not write more.
			// we obviously need to consider this only for the last block.
			uint64_t all_blocks = 0;
			for (uint8_t id = 0; id < blocks(); ++id)
				all_blocks += block_size (sbn);
			const uint64_t diff = all_blocks - _size;
			max_bytes -= diff;
		}
		auto tmp_start = start;
		uint64_t bytes_written = de_interleaving (tmp_start, end, max_bytes,
																	new_skip);
		written += bytes_written;
		uint64_t bytes_and_skip = new_skip + bytes_written;
		new_skip = bytes_and_skip %
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
		if (bytes_written == 0)
			return written;
		//new_skip = block_size (sbn) %
		//			sizeof(typename std::iterator_traits<Fwd_It>::value_type);
		// if we ended decoding in the middle of a Fwd_It, do not advance
		// start too much, or we will end up having additional zeros.
		if (new_skip == 0) {
			start = tmp_start;
		} else {
			uint64_t it_written = bytes_and_skip /
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
			// RaptorQ handles at most 881GB per rfc, so
			// casting uint64 to int64 is safe
			// we can not do "--start" since it's a forward iterator
			start += std::max (static_cast<int64_t> (0),
										static_cast<int64_t> (it_written - 1));
		}
	}
	return written;
}

template <typename In_It, typename Fwd_It>
uint64_t Decoder<In_It, Fwd_It>::decode_block_bytes (Fwd_It &start,
															const Fwd_It end,
															const uint8_t skip,
															const uint8_t sbn)
{
	if (sbn >= _blocks)
		return 0;

	std::shared_ptr<RaptorQ__v1::Impl::Decoder<In_It>> dec_ptr = nullptr;
	std::unique_lock<std::mutex> lock (_mtx);
	auto it = decoders.find (sbn);

	if (it == decoders.end())
		return 0;	// did not receiveany data yet.

	if (use_pool) {
		dec_ptr = it->second.dec;
		lock.unlock();
		if (!dec_ptr->ready())
			return 0;	// did not receive enough data, or could not decode yet.
	} else {
		dec_ptr = it->second.dec;
		lock.unlock();
		if (!dec_ptr->ready()) {
			if (!dec_ptr->can_decode())
				return 0;
			Work_State keep_working = Work_State::KEEP_WORKING;
			dec_ptr->decode (&keep_working);
			if (!dec_ptr->ready())
				return 0;
		}
	}
	// decoder has decoded the block

	Impl::De_Interleaver<Fwd_It> de_interleaving (dec_ptr->get_symbols(),
													_sub_blocks, _alignment);
	uint64_t max_bytes = block_size (sbn);
	if (sbn == (blocks() - 1)) {
		// size of the data (_size) is different from the sum of the size of
		// all blocks. get the real size, so we do not write more.
		// we obviously need to consider this only for the last block.
		uint64_t all_blocks = 0;
		for (uint8_t id = 0; id < blocks(); ++id)
			all_blocks += block_size (sbn);
		const uint64_t diff = all_blocks - _size;
		max_bytes -= diff;
	}
	return de_interleaving (start, end, max_bytes, skip);
}

template <typename In_It, typename Fwd_It>
std::pair<size_t, uint8_t> Decoder<In_It, Fwd_It>::decode_aligned (
														Fwd_It &start,
														const Fwd_It end,
														const uint8_t skip)
{
	const uint64_t bytes = decode_bytes (start, end, skip);
	const uint64_t skip_and_bytes = skip + bytes;
	const uint64_t iterators = skip_and_bytes /
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
	const uint8_t new_skip = skip_and_bytes %
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
	return {iterators, new_skip};
}

template <typename In_It, typename Fwd_It>
std::pair<size_t, uint8_t> Decoder<In_It, Fwd_It>::decode_block_aligned (
														Fwd_It &start,
														const Fwd_It end,
														const uint8_t skip,
														const uint8_t sbn)
{
	const uint64_t bytes = decode_block_bytes (start, end, skip, sbn);
	const uint64_t skip_and_bytes = skip + bytes;
	const uint64_t iterators = skip_and_bytes /
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
	const uint8_t new_skip = skip_and_bytes %
					sizeof(typename std::iterator_traits<Fwd_It>::value_type);
	return {iterators, new_skip};
}

template <typename In_It, typename Fwd_It>
uint64_t Decoder<In_It, Fwd_It>::bytes() const
{
	return _size;
}

template <typename In_It, typename Fwd_It>
uint8_t Decoder<In_It, Fwd_It>::blocks() const
{
	return static_cast<uint8_t> (part.num (0) + part.num (1));
}

template <typename In_It, typename Fwd_It>
uint32_t Decoder<In_It, Fwd_It>::block_size (const uint8_t sbn) const
{
	if (sbn < part.num (0)) {
		return part.size (0) * _symbol_size;
	} else if (sbn - part.num (0) < part.num (1)) {
		return part.size (1) * _symbol_size;
	}
	return 0;
}

template <typename In_It, typename Fwd_It>
uint16_t Decoder<In_It, Fwd_It>::symbol_size() const
{
	return _symbol_size;
}
template <typename In_It, typename Fwd_It>
uint16_t Decoder<In_It, Fwd_It>::symbols (const uint8_t sbn) const
{
	if (sbn < part.num (0)) {
		return part.size (0);
	} else if (sbn - part.num (0) < part.num (1)) {
		return part.size (1);
	}
	return 0;
}

}	// RaptorQ__v1