Function compress

src/jrd/btr.cpp:2773–3325

static void compress(thread_db* tdbb,
					 const dsc* desc,
					 const SSHORT matchScale,
					 temporary_key* key,
					 USHORT itype,
					 bool descending, USHORT key_type,
					 bool* forceInclude)
{
/**************************************
 *
 *	c o m p r e s s
 *
 **************************************
 *
 * Functional description
 *	Compress a data value into an index key.
 *
 **************************************/
	if (!desc) // this indicates NULL
	{
		const UCHAR pad = 0;
		key->key_flags &= ~key_empty;
		// AB: NULL should be threated as lowest value possible.
		//     Therefore don't complement pad when we have an ascending index.
		if (descending)
		{
			// DESC NULLs are stored as 1 byte
			key->key_data[0] = pad;
			key->key_length = 1;
		}
		else
			key->key_length = 0; // ASC NULLs are stored with no data

		fb_assert(!key->key_next);
		return;
	}

	// For descending index and new index structure we insert 0xFE at the beginning.
	// This is only done for values which begin with 0xFE (254) or 0xFF (255) and
	// is needed to make a difference between a NULL state and a VALUE.
	// Note! By descending index key is complemented after this compression routine.
	// Further a NULL state is always returned as 1 byte 0xFF (descending index).
	const UCHAR desc_end_value_prefix = 0x01; // ~0xFE
	const UCHAR desc_end_value_check = 0x00; // ~0xFF;

	const Database* dbb = tdbb->getDatabase();
	bool first_key = true;
	VaryStr<MAX_KEY * 4> buffer;
	size_t multiKeyLength;
	UCHAR* ptr;
	UCHAR* p = key->key_data;
	SSHORT scale = matchScale ? matchScale : desc->dsc_scale;

	if (itype == idx_string || itype == idx_byte_array || itype == idx_metadata ||
		itype == idx_decimal || itype == idx_bcd || itype >= idx_first_intl_string)
	{
		temporary_key* root_key = key;
		bool has_next;