Remove pre-order and post-order traversal logic for red-black trees.
This code isn't used, and there's no clear reason why anybody would ever want to use it. These traversal mechanisms don't yield a visitation order that is semantically meaningful for any external purpose, nor are they any faster or simpler than the left-to-right or right-to-left traversals. (In fact, some rough testing suggests they are slower :-(.) Moreover, these mechanisms are impossible to test in any arm's-length fashion; doing so requires knowledge of the red-black tree's internal implementation. Hence, let's just jettison them. Discussion: https://postgr.es/m/17735.1505003111@sss.pgh.pa.us
This commit is contained in:
Tom Lane
parent
c824c7e29f
commit
f80e782a6b
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@ -62,17 +62,6 @@ struct RBTree
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static RBNode sentinel = {RBBLACK, RBNIL, RBNIL, NULL};
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/*
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* Values used in the RBTreeIterator.next_state field, with an
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* InvertedWalk iterator.
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*/
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typedef enum InvertedWalkNextStep
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{
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NextStepBegin,
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NextStepUp,
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NextStepLeft,
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NextStepRight
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} InvertedWalkNextStep;
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/*
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* rb_create: create an empty RBTree
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@ -567,6 +556,7 @@ rb_delete_node(RBTree *rb, RBNode *z)
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RBNode *x,
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*y;
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/* This is just paranoia: we should only get called on a valid node */
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if (!z || z == RBNIL)
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return;
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@ -730,114 +720,6 @@ rb_right_left_iterator(RBTreeIterator *iter)
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return iter->last_visited;
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}
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static RBNode *
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rb_direct_iterator(RBTreeIterator *iter)
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{
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if (iter->last_visited == NULL)
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{
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iter->last_visited = iter->rb->root;
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return iter->last_visited;
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}
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if (iter->last_visited->left != RBNIL)
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{
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iter->last_visited = iter->last_visited->left;
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return iter->last_visited;
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}
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do
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{
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if (iter->last_visited->right != RBNIL)
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{
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iter->last_visited = iter->last_visited->right;
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break;
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}
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/* go up and one step right */
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for (;;)
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{
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RBNode *came_from = iter->last_visited;
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iter->last_visited = iter->last_visited->parent;
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if (iter->last_visited == NULL)
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{
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iter->is_over = true;
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break;
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}
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if ((iter->last_visited->right != came_from) && (iter->last_visited->right != RBNIL))
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{
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iter->last_visited = iter->last_visited->right;
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return iter->last_visited;
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}
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}
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}
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while (iter->last_visited != NULL);
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return iter->last_visited;
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}
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static RBNode *
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rb_inverted_iterator(RBTreeIterator *iter)
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{
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RBNode *came_from;
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RBNode *current;
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current = iter->last_visited;
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loop:
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switch ((InvertedWalkNextStep) iter->next_step)
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{
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/* First call, begin from root */
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case NextStepBegin:
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current = iter->rb->root;
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iter->next_step = NextStepLeft;
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goto loop;
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case NextStepLeft:
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while (current->left != RBNIL)
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current = current->left;
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iter->next_step = NextStepRight;
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goto loop;
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case NextStepRight:
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if (current->right != RBNIL)
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{
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current = current->right;
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iter->next_step = NextStepLeft;
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goto loop;
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}
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else /* not moved - return current, then go up */
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iter->next_step = NextStepUp;
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break;
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case NextStepUp:
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came_from = current;
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current = current->parent;
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if (current == NULL)
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{
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iter->is_over = true;
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break; /* end of iteration */
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}
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else if (came_from == current->right)
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{
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/* return current, then continue to go up */
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break;
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}
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else
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{
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/* otherwise we came from the left */
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Assert(came_from == current->left);
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iter->next_step = NextStepRight;
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goto loop;
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}
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}
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iter->last_visited = current;
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return current;
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}
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/*
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* rb_begin_iterate: prepare to traverse the tree in any of several orders
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*
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@ -849,7 +731,7 @@ loop:
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* tree are allowed.
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*
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* The iterator state is stored in the 'iter' struct. The caller should
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* treat it as opaque struct.
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* treat it as an opaque struct.
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*/
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void
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rb_begin_iterate(RBTree *rb, RBOrderControl ctrl, RBTreeIterator *iter)
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@ -867,13 +749,6 @@ rb_begin_iterate(RBTree *rb, RBOrderControl ctrl, RBTreeIterator *iter)
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case RightLeftWalk: /* visit right, then self, then left */
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iter->iterate = rb_right_left_iterator;
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break;
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case DirectWalk: /* visit self, then left, then right */
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iter->iterate = rb_direct_iterator;
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break;
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case InvertedWalk: /* visit left, then right, then self */
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iter->iterate = rb_inverted_iterator;
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iter->next_step = NextStepBegin;
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break;
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default:
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elog(ERROR, "unrecognized rbtree iteration order: %d", ctrl);
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}
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@ -35,9 +35,7 @@ typedef struct RBTree RBTree;
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typedef enum RBOrderControl
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{
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LeftRightWalk, /* inorder: left child, node, right child */
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RightLeftWalk, /* reverse inorder: right, node, left */
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DirectWalk, /* preorder: node, left child, right child */
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InvertedWalk /* postorder: left child, right child, node */
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RightLeftWalk /* reverse inorder: right, node, left */
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} RBOrderControl;
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/*
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@ -52,7 +50,6 @@ struct RBTreeIterator
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RBTree *rb;
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RBNode *(*iterate) (RBTreeIterator *iter);
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RBNode *last_visited;
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char next_step;
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bool is_over;
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};
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