Function checkForLowerKeySkip

src/jrd/btr.cpp:1057–1128

static void checkForLowerKeySkip(bool& skipLowerKey,
								 const bool partLower,
								 const IndexNode& node,
								 const temporary_key& lower,
								 const index_desc& idx,
								 const IndexRetrieval* retrieval)
{
	if (node.prefix == 0)
	{
		// If the prefix is 0 we have a full key.
		// (first node on every new page for example has prefix zero)
		if (partLower)
		{
			// With multi-segment compare first part of data with lowerKey
			skipLowerKey = ((lower.key_length <= node.length) &&
				(memcmp(node.data, lower.key_data, lower.key_length) == 0));

			if (skipLowerKey && (node.length > lower.key_length))
			{
				// We've bigger data in the node than in the lowerKey,
				// now check the segment-number
				const UCHAR* segp = node.data + lower.key_length;

				const USHORT segnum =
					idx.idx_count - (UCHAR)((idx.idx_flags & idx_descending) ? ((*segp) ^ -1) : *segp);

				if (segnum < retrieval->irb_lower_count)
					skipLowerKey = false;
			}
		}
		else
		{
			// Compare full data with lowerKey
			skipLowerKey = ((lower.key_length == node.length) &&
				(memcmp(node.data, lower.key_data, lower.key_length) == 0));
		}
	}
	else
	{
		if ((lower.key_length == node.prefix + node.length) ||
			((lower.key_length <= node.prefix + node.length) && partLower))
		{
			const UCHAR* p = node.data, *q = lower.key_data + node.prefix;
			const UCHAR* const end = lower.key_data + lower.key_length;
			while (q < end)
			{
				if (*p++ != *q++)
				{
					skipLowerKey = false;
					break;
				}
			}

			if ((q >= end) && (p < node.data + node.length) && skipLowerKey && partLower)
			{
				const bool descending = idx.idx_flags & idx_descending;

				// since key length always is multiplier of (STUFF_COUNT + 1) (for partial