139 lines
4.2 KiB
Nim
139 lines
4.2 KiB
Nim
# Nimbus
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# Copyright (c) 2018 Status Research & Development GmbH
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# Licensed under either of
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# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
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# http://www.apache.org/licenses/LICENSE-2.0)
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# * MIT license ([LICENSE-MIT](LICENSE-MIT) or
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# http://opensource.org/licenses/MIT)
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# at your option. This file may not be copied, modified, or distributed except
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# according to those terms.
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import
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./rbtree_desc,
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./rbtree_rotate,
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../results
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{.push raises: [Defect].}
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# ------------------------------------------------------------------------------
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# Public
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# ------------------------------------------------------------------------------
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proc rbTreeDelete*[C,K](rbt: RbTreeRef[C,K]; key: K): RbResult[C] =
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## Generic red-black tree function, removes a node from the red-black tree.
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## The node to be removed wraps a data container `casket` matching the
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## argument `key`, i.e. `rbt.cmp(casket,key) == 0`.
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##
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## If the node was successfully deleted, the function returns the matching
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## `casket` data container. Otherwise, there was no such node with a matching
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## `casket` in the tree.
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##
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## :Ackn:
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## `jsw_rberase()` from jsw_rbtree.c from captured C library
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## `jsw_rbtree.zip <https://web.archive.org/web/20160428112900/http://eternallyconfuzzled.com/libs/jsw_rbtree.zip>`_.
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##
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if rbt.root.isNil:
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return err(rbEmptyTree)
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var
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dir = rbRight # start here
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found: RbNodeRef[C] # node to be removed (if any)
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head = RbNodeRef[C](
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link: [nil, rbt.root]) # black false tree root
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# ancestry line: g -> p -> q
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grandParent: RbNodeRef[C] # grandparent => NIL
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parent: RbNodeRef[C] # parent => NIL
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q = head # iterator
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# Search and push a red node down to fix red violations as we go
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while not q.link[dir].isNil:
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# Move the helpers down
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grandParent = parent
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parent = q
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q = q.link[dir]
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let
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last = dir
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diff = rbt.cmp(q.casket,key)
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dir = (diff < 0).toDir
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# Save matching node and keep going, removal job is done below this loop
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if diff == 0:
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found = q
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# Push the red node down with rotations and color flips
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if q.isRed or q.link[dir].isRed:
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continue
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if q.link[not dir].isRed:
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let qrs = q.rbTreeRotateSingle(dir)
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parent.link[last] = qrs
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parent = qrs
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# Mark traversal path unusable
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rbt.dirty = rbt.dirty or rbTreeReBalancedFlag
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continue
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# Now: not q.link[not dir].isRed
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let sibling = parent.link[not last]
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if sibling.isNil:
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continue
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# Note that `link.isRed` => `not link.isNil`
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if not sibling.linkLeft.isRed and not sibling.linkRight.isRed:
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# Color flip
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parent.isRed = false # aka black
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sibling.isRed = true
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q.isRed = true
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continue
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let dir2 = (grandParent.linkRight == parent).toDir
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if sibling.link[last].isRed:
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grandParent.link[dir2] = parent.rbTreeRotateDouble(last)
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rbt.dirty = rbt.dirty or rbTreeReBalancedFlag
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elif sibling.link[not last].isRed:
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grandParent.link[dir2] = parent.rbTreeRotateSingle(last)
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rbt.dirty = rbt.dirty or rbTreeReBalancedFlag
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# Ensure correct coloring
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q.isRed = true
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let ggp2 = grandParent.link[dir2]
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ggp2.isRed = true
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ggp2.linkLeft.isRed = false # aka black
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ggp2.linkRight.isRed = false # aka black
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# End while
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# Replace and remove the saved node */
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if found.isNil:
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result = err(rbNotFound)
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else:
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result = ok(found.casket)
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found.casket = q.casket
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let
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dirX = (parent.linkRight == q).toDir
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dirY = q.linkLeft.isNil.toDir
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parent.link[dirX] = q.link[dirY];
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# clear node cache if this was the one to be deleted
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if not rbt.cache.isNil and rbt.cmp(rbt.cache.casket,key) == 0:
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rbt.cache = nil
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q = nil # some hint for the GC to recycle that node
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rbt.size.dec
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rbt.dirty = rbt.dirty or rbTreeReBalancedFlag
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# Update the root (it may be different)
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rbt.root = head.linkRight
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# Mark the root black for simplified logic
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if not rbt.root.isNil:
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rbt.root.isRed = false # aka black
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# ------------------------------------------------------------------------------
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# End
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# ------------------------------------------------------------------------------
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