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Optimize XPath sorting for sorted sequences

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XPath evaluation frequently produces sequences that are sorted but are not
tagged as such (area for improvement...). Doing a linear scan before
sorting is cheap and results in tremendous speedup for already sorted
sequences (especially if document_buffer_order optimization does not
apply).

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1049 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
Arseny Kapoulkine 2014-10-05 04:20:38 +00:00
parent 42219590f3
commit e66356715c
1 changed files with 26 additions and 3 deletions
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23
src/pugixml.cpp
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@ -7498,16 +7498,39 @@ PUGI__NS_END
// Internal node set class // Internal node set class
PUGI__NS_BEGIN PUGI__NS_BEGIN
PUGI__FN xpath_node_set::type_t xpath_get_order(const xpath_node* begin, const xpath_node* end)
{
if (end - begin < 2)
return xpath_node_set::type_sorted;
document_order_comparator cmp;
bool first = cmp(begin[0], begin[1]);
for (const xpath_node* it = begin + 1; it + 1 < end; ++it)
if (cmp(it[0], it[1]) != first)
return xpath_node_set::type_unsorted;
return first ? xpath_node_set::type_sorted : xpath_node_set::type_sorted_reverse;
}
PUGI__FN xpath_node_set::type_t xpath_sort(xpath_node* begin, xpath_node* end, xpath_node_set::type_t type, bool rev) PUGI__FN xpath_node_set::type_t xpath_sort(xpath_node* begin, xpath_node* end, xpath_node_set::type_t type, bool rev)
{ {
xpath_node_set::type_t order = rev ? xpath_node_set::type_sorted_reverse : xpath_node_set::type_sorted; xpath_node_set::type_t order = rev ? xpath_node_set::type_sorted_reverse : xpath_node_set::type_sorted;
if (type == xpath_node_set::type_unsorted) if (type == xpath_node_set::type_unsorted)
{
xpath_node_set::type_t sorted = xpath_get_order(begin, end);
if (sorted == xpath_node_set::type_unsorted)
{ {
sort(begin, end, document_order_comparator()); sort(begin, end, document_order_comparator());
type = xpath_node_set::type_sorted; type = xpath_node_set::type_sorted;
} }
else
type = sorted;
}
if (type != order) reverse(begin, end); if (type != order) reverse(begin, end);