Function find_area_start_point

src/jrd/btr.cpp:4712–4933

static UCHAR* find_area_start_point(btree_page* bucket, const temporary_key* key,
									UCHAR* value,
									USHORT* return_prefix, bool descending,
									int retrieval, RecordNumber find_record_number)
{
/**************************************
 *
 *	f i n d _ a r e a _ s t a r t _ p o i n t
 *
 **************************************
 *
 * Functional description
 *	Locate and return a pointer to a start area.
 *	The starting nodes for a area are
 *  defined with jump nodes. A jump node
 *  contains the prefix information for
 *  a node at a specific offset.
 *
 **************************************/
	const bool useFindRecordNumber = (find_record_number != NO_VALUE);
	const bool leafPage = (bucket->btr_level == 0);
	const UCHAR* keyPointer = key->key_data;
	const UCHAR* const keyEnd = keyPointer + key->key_length;

	// Retrieve jump information.
	UCHAR* pointer = bucket->btr_nodes;
	UCHAR n = bucket->btr_jump_count;

	// Set begin of page as default.
	IndexJumpNode prevJumpNode;
	prevJumpNode.offset = BTR_SIZE + bucket->btr_jump_size;
	prevJumpNode.prefix = 0;
	prevJumpNode.length = 0;

	temporary_key jumpKey;
	jumpKey.key_length = 0;
	jumpKey.key_flags = 0;

	USHORT prefix = 0;
	USHORT testPrefix = 0;

	while (n)
	{
		IndexJumpNode jumpNode;
		pointer = jumpNode.readJumpNode(pointer);

		IndexNode node;
		node.readNode((UCHAR*) bucket + jumpNode.offset, leafPage);

		// jumpKey will hold complete data off referenced node
		memcpy(jumpKey.key_data + jumpNode.prefix, jumpNode.data, jumpNode.length);
		memcpy(jumpKey.key_data + node.prefix, node.data, node.length);
		jumpKey.key_length = node.prefix + node.length;

		keyPointer = key->key_data + jumpNode.prefix;
		const UCHAR* q = jumpKey.key_data + jumpNode.prefix;
		const UCHAR* const nodeEnd = jumpKey.key_data + jumpKey.key_length;
		bool done = false;