Function BTR_make_null_key

src/jrd/btr.cpp:2033–2101

void BTR_make_null_key(thread_db* tdbb, const index_desc* idx, temporary_key* key)
{
/**************************************
 *
 *	B T R _ m a k e _ n u l l _ k e y
 *
 **************************************
 *
 * Functional description
 *	Construct a (possibly) compound search key consist from
 *  all null values. This is worked only for ODS11 and later
 *
 **************************************/
	temporary_key temp;
	temp.key_flags = 0;
	temp.key_length = 0;

	SET_TDBB(tdbb);

	fb_assert(idx != NULL);
	fb_assert(key != NULL);

	key->key_flags = 0;
	key->key_nulls = (1 << idx->idx_count) - 1;

	const bool descending = (idx->idx_flags & idx_descending);

	const index_desc::idx_repeat* tail = idx->idx_rpt;

	// If the index is a single segment index, don't sweat the compound stuff
	if ((idx->idx_count == 1) || (idx->idx_flags & idx_expression))
	{
		compress(tdbb, nullptr, 0, key, tail->idx_itype, descending, INTL_KEY_SORT, nullptr);
	}
	else
	{
		// Make a compound key
		UCHAR* p = key->key_data;
		SSHORT stuff_count = 0;
		temp.key_flags |= key_empty;

		for (USHORT n = 0; n < idx->idx_count; n++, tail++)
		{
			for (; stuff_count; --stuff_count)
				*p++ = 0;

			compress(tdbb, nullptr, 0, &temp, tail->idx_itype, descending, INTL_KEY_SORT, nullptr);

			const UCHAR* q = temp.key_data;
			for (USHORT l = temp.key_length; l; --l, --stuff_count)
			{
				if (stuff_count == 0)
				{
					*p++ = idx->idx_count - n;
					stuff_count = STUFF_COUNT;
				}
				*p++ = *q++;
			}