Method truncate

src/jrd/sqz.cpp:268–338

}

ULONG Compressor::truncate(ULONG outLength)
{
/**************************************
 *
 *	Reset to pack only a leading fragment of the input, restricted by the output length.
 *	Return the number of leading input bytes that fit the given output length.
 *
 **************************************/
	fb_assert(m_length > outLength);

	if (m_runs.isEmpty())
	{
		m_length = outLength;
		return outLength;
	}

	auto space = (int) outLength;
	ULONG inLength = 0;
	ULONG keepRuns = 0;
	m_length = 0;

	for (auto& length : m_runs)
	{
		if (--space <= 0)
			break;

		if (length < 0)
		{
			const auto zipLength = (unsigned) -length;
			const auto runLength = 1 + adjustRunLength(zipLength);

			if ((space -= runLength) < 0)
				break;

			m_length += runLength + 1;
			inLength += zipLength;
		}
		else
		{
			fb_assert(length > 0 && length <= MAX_NONCOMP_RUN);

			if ((space -= length) < 0)
			{
				length += space; // how many bytes fit

				m_length += length + 1;
				inLength += length;
				keepRuns++;
				break;
			}

			m_length += length + 1;
			inLength += length;
		}

		keepRuns++;
	}