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Add missing inequality searches to rbtree

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PostgreSQL contains the implementation of the red-black tree.  The red-black
tree is the ordered data structure, and one of its advantages is the ability
to do inequality searches.  This commit adds rbt_find_less() and
rbt_find_great() functions implementing these searches.  While these searches
aren't yet used in the core code, they might be useful for extensions.

Discussion: https://postgr.es/m/CAGRrpzYE8-7GCoaPjOiL9T_HY605MRax-2jgTtLq236uksZ1Sw%40mail.gmail.com
Author: Steve Chavez, Alexander Korotkov
Reviewed-by: Alexander Korotkov
This commit is contained in:
Alexander Korotkov
2022-07-08 21:51:26 +03:00
parent 8d51d7f403
commit e57519a463
3 changed files with 166 additions and 0 deletions
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62
src/backend/lib/rbtree.c
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@@ -161,6 +161,68 @@ rbt_find(RBTree *rbt, const RBTNode *data)
return NULL;
}
/*
* rbt_find_great: search for a greater value in an RBTree
*
* If equal_match is true, this will be a great or equal search.
*
* Returns the matching tree entry, or NULL if no match is found.
*/
RBTNode *
rbt_find_great(RBTree *rbt, const RBTNode *data, bool equal_match)
{
RBTNode *node = rbt->root;
RBTNode *greater = NULL;
while (node != RBTNIL)
{
int cmp = rbt->comparator(data, node, rbt->arg);
if (equal_match && cmp == 0)
return node;
else if (cmp < 0)
{
greater = node;
node = node->left;
}
else
node = node->right;
}
return greater;
}
/*
* rbt_find_less: search for a lesser value in an RBTree
*
* If equal_match is true, this will be a less or equal search.
*
* Returns the matching tree entry, or NULL if no match is found.
*/
RBTNode *
rbt_find_less(RBTree *rbt, const RBTNode *data, bool equal_match)
{
RBTNode *node = rbt->root;
RBTNode *lesser = NULL;
while (node != RBTNIL)
{
int cmp = rbt->comparator(data, node, rbt->arg);
if (equal_match && cmp == 0)
return node;
else if (cmp > 0)
{
lesser = node;
node = node->right;
}
else
node = node->left;
}
return lesser;
}
/*
* rbt_leftmost: fetch the leftmost (smallest-valued) tree node.
* Returns NULL if tree is empty.