Move lib/rbtree to lib/containers

1 files changed, 522 insertions, 0 deletions

diff --git a/lib/containers/rbtree.go b/lib/containers/rbtree.go
new file mode 100644
index 0000000..6bffc02
--- /dev/null
+++ b/lib/containers/rbtree.go
@@ -0,0 +1,522 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package containers
+
+import (
+	"fmt"
+	"reflect"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/util"
+)
+
+type Color bool
+
+const (
+	Black = Color(false)
+	Red   = Color(true)
+)
+
+type RBNode[V any] struct {
+	Parent, Left, Right *RBNode[V]
+
+	Color Color
+
+	Value V
+}
+
+func (node *RBNode[V]) getColor() Color {
+	if node == nil {
+		return Black
+	}
+	return node.Color
+}
+
+type RBTree[K util.Ordered[K], V any] struct {
+	KeyFn func(V) K
+	root  *RBNode[V]
+}
+
+func (t *RBTree[K, V]) Walk(fn func(*RBNode[V]) error) error {
+	return t.root.walk(fn)
+}
+
+func (node *RBNode[V]) walk(fn func(*RBNode[V]) error) error {
+	if node == nil {
+		return nil
+	}
+	if err := node.Left.walk(fn); err != nil {
+		return err
+	}
+	if err := fn(node); err != nil {
+		return err
+	}
+	if err := node.Right.walk(fn); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Search the tree for a value that satisfied the given callbackk
+// function.  A return value of 0 means to to return this value; <0
+// means to go left on the tree (the value is too high), >0 means to
+// go right on th etree (the value is too low).
+//
+//             +-----+
+//             | v=8 | == 0 : this is it
+//             +-----+
+//            /       \
+//           /         \
+//     <0 : go left   >0 : go right
+//         /             \
+//      +---+          +---+
+//      | 7 |          | 9 |
+//      +---+          +---+
+//
+// Returns nil if no such value is found.
+//
+// Search is good for advanced lookup, like when a range of values is
+// acceptable.  For simple exact-value lookup, use Lookup.
+func (t *RBTree[K, V]) Search(fn func(V) int) *RBNode[V] {
+	ret, _ := t.root.search(fn)
+	return ret
+}
+
+func (node *RBNode[V]) search(fn func(V) int) (exact, nearest *RBNode[V]) {
+	var prev *RBNode[V]
+	for {
+		if node == nil {
+			return nil, prev
+		}
+		direction := fn(node.Value)
+		prev = node
+		switch {
+		case direction < 0:
+			node = node.Left
+		case direction == 0:
+			return node, nil
+		case direction > 0:
+			node = node.Right
+		}
+	}
+}
+
+func (t *RBTree[K, V]) exactKey(key K) func(V) int {
+	return func(val V) int {
+		valKey := t.KeyFn(val)
+		return key.Cmp(valKey)
+	}
+}
+
+// Lookup looks up the value for an exact key.  If no such value
+// exists, nil is returned.
+func (t *RBTree[K, V]) Lookup(key K) *RBNode[V] {
+	return t.Search(t.exactKey(key))
+}
+
+// Min returns the minimum value stored in the tree, or nil if the
+// tree is empty.
+func (t *RBTree[K, V]) Min() *RBNode[V] {
+	return t.root.min()
+}
+
+func (node *RBNode[V]) min() *RBNode[V] {
+	if node == nil {
+		return nil
+	}
+	for {
+		if node.Left == nil {
+			return node
+		}
+		node = node.Left
+	}
+}
+
+// Max returns the maximum value stored in the tree, or nil if the
+// tree is empty.
+func (t *RBTree[K, V]) Max() *RBNode[V] {
+	return t.root.max()
+}
+
+func (node *RBNode[V]) max() *RBNode[V] {
+	if node == nil {
+		return nil
+	}
+	for {
+		if node.Right == nil {
+			return node
+		}
+		node = node.Right
+	}
+}
+
+func (t *RBTree[K, V]) Next(cur *RBNode[V]) *RBNode[V] {
+	return cur.next()
+}
+
+func (cur *RBNode[V]) next() *RBNode[V] {
+	if cur.Right != nil {
+		return cur.Right.min()
+	}
+	child, parent := cur, cur.Parent
+	for parent != nil && child == parent.Right {
+		child, parent = parent, parent.Parent
+	}
+	return parent
+}
+
+func (t *RBTree[K, V]) Prev(cur *RBNode[V]) *RBNode[V] {
+	return cur.prev()
+}
+
+func (cur *RBNode[V]) prev() *RBNode[V] {
+	if cur.Left != nil {
+		return cur.Left.max()
+	}
+	child, parent := cur, cur.Parent
+	for parent != nil && child == parent.Left {
+		child, parent = parent, parent.Parent
+	}
+	return parent
+}
+
+// SearchRange is like Search, but returns all nodes that match the
+// function; assuming that they are contiguous.
+func (t *RBTree[K, V]) SearchRange(fn func(V) int) []V {
+	middle := t.Search(fn)
+	if middle == nil {
+		return nil
+	}
+	ret := []V{middle.Value}
+	for node := t.Prev(middle); node != nil && fn(node.Value) == 0; node = t.Prev(node) {
+		ret = append(ret, node.Value)
+	}
+	util.ReverseSlice(ret)
+	for node := t.Next(middle); node != nil && fn(node.Value) == 0; node = t.Next(node) {
+		ret = append(ret, node.Value)
+	}
+	return ret
+}
+
+func (t *RBTree[K, V]) Equal(u *RBTree[K, V]) bool {
+	if (t == nil) != (u == nil) {
+		return false
+	}
+	if t == nil {
+		return true
+	}
+
+	var tSlice []V
+	_ = t.Walk(func(node *RBNode[V]) error {
+		tSlice = append(tSlice, node.Value)
+		return nil
+	})
+
+	var uSlice []V
+	_ = u.Walk(func(node *RBNode[V]) error {
+		uSlice = append(uSlice, node.Value)
+		return nil
+	})
+
+	return reflect.DeepEqual(tSlice, uSlice)
+}
+
+func (t *RBTree[K, V]) parentChild(node *RBNode[V]) **RBNode[V] {
+	switch {
+	case node.Parent == nil:
+		return &t.root
+	case node.Parent.Left == node:
+		return &node.Parent.Left
+	case node.Parent.Right == node:
+		return &node.Parent.Right
+	default:
+		panic(fmt.Errorf("node %p is not a child of its parent %p", node, node.Parent))
+	}
+}
+
+func (t *RBTree[K, V]) leftRotate(x *RBNode[V]) {
+	//        p                        p
+	//        |                        |
+	//      +---+                    +---+
+	//      | x |                    | y |
+	//      +---+                    +---+
+	//     /     \         =>       /     \
+	//    a    +---+              +---+    c
+	//         | y |              | x |
+	//         +---+              +---+
+	//        /     \            /     \
+	//       b       c          a       b
+
+	// Define 'p', 'x', 'y', and 'b' per the above diagram.
+	p := x.Parent
+	pChild := t.parentChild(x)
+	y := x.Right
+	b := y.Left
+
+	// Move things around
+
+	y.Parent = p
+	*pChild = y
+
+	x.Parent = y
+	y.Left = x
+
+	if b != nil {
+		b.Parent = x
+	}
+	x.Right = b
+}
+
+func (t *RBTree[K, V]) rightRotate(y *RBNode[V]) {
+	//           |                |
+	//         +---+            +---+
+	//         | y |            | x |
+	//         +---+            +---+
+	//        /     \    =>    /     \
+	//      +---+    c        a    +---+
+	//      | x |                  | y |
+	//      +---+                  +---+
+	//     /     \                /     \
+	//    a       b              b       c
+
+	// Define 'p', 'x', 'y', and 'b' per the above diagram.
+	p := y.Parent
+	pChild := t.parentChild(y)
+	x := y.Left
+	b := x.Right
+
+	// Move things around
+
+	x.Parent = p
+	*pChild = x
+
+	y.Parent = x
+	x.Right = y
+
+	if b != nil {
+		b.Parent = y
+	}
+	y.Left = b
+}
+
+func (t *RBTree[K, V]) Insert(val V) {
+	// Naive-insert
+
+	key := t.KeyFn(val)
+	exact, parent := t.root.search(t.exactKey(key))
+	if exact != nil {
+		exact.Value = val
+		return
+	}
+
+	node := &RBNode[V]{
+		Color:  Red,
+		Parent: parent,
+		Value:  val,
+	}
+	if parent == nil {
+		t.root = node
+	} else if key.Cmp(t.KeyFn(parent.Value)) < 0 {
+		parent.Left = node
+	} else {
+		parent.Right = node
+	}
+
+	// Re-balance
+	//
+	// This is closely based on the algorithm presented in CLRS
+	// 3e.
+
+	for node.Parent.getColor() == Red {
+		if node.Parent == node.Parent.Parent.Left {
+			uncle := node.Parent.Parent.Right
+			if uncle.getColor() == Red {
+				node.Parent.Color = Black
+				uncle.Color = Black
+				node.Parent.Parent.Color = Red
+				node = node.Parent.Parent
+			} else {
+				if node == node.Parent.Right {
+					node = node.Parent
+					t.leftRotate(node)
+				}
+				node.Parent.Color = Black
+				node.Parent.Parent.Color = Red
+				t.rightRotate(node.Parent.Parent)
+			}
+		} else {
+			uncle := node.Parent.Parent.Left
+			if uncle.getColor() == Red {
+				node.Parent.Color = Black
+				uncle.Color = Black
+				node.Parent.Parent.Color = Red
+				node = node.Parent.Parent
+			} else {
+				if node == node.Parent.Left {
+					node = node.Parent
+					t.rightRotate(node)
+				}
+				node.Parent.Color = Black
+				node.Parent.Parent.Color = Red
+				t.leftRotate(node.Parent.Parent)
+			}
+		}
+	}
+	t.root.Color = Black
+}
+
+func (t *RBTree[K, V]) transplant(old, new *RBNode[V]) {
+	*t.parentChild(old) = new
+	if new != nil {
+		new.Parent = old.Parent
+	}
+}
+
+func (t *RBTree[K, V]) Delete(key K) {
+	nodeToDelete := t.Lookup(key)
+	if nodeToDelete == nil {
+		return
+	}
+
+	// This is closely based on the algorithm presented in CLRS
+	// 3e.
+
+	var nodeToRebalance *RBNode[V]
+	var nodeToRebalanceParent *RBNode[V] // in case 'nodeToRebalance' is nil, which it can be
+	needsRebalance := nodeToDelete.Color == Black
+
+	switch {
+	case nodeToDelete.Left == nil:
+		nodeToRebalance = nodeToDelete.Right
+		nodeToRebalanceParent = nodeToDelete.Parent
+		t.transplant(nodeToDelete, nodeToDelete.Right)
+	case nodeToDelete.Right == nil:
+		nodeToRebalance = nodeToDelete.Left
+		nodeToRebalanceParent = nodeToDelete.Parent
+		t.transplant(nodeToDelete, nodeToDelete.Left)
+	default:
+		// The node being deleted has a child on both sides,
+		// so we've go to reshuffle the parents a bit to make
+		// room for those children.
+		next := nodeToDelete.next()
+		if next.Parent == nodeToDelete {
+			//         p                  p
+			//         |                  |
+			//      +-----+            +-----+
+			//      | ntd |            | nxt |
+			//      +-----+            +-----+
+			//      /     \       =>   /     \
+			//     a     +-----+      a      b
+			//           | nxt |
+			//           +-----+
+			//            /   \
+			//          nil   b
+			nodeToRebalance = next.Right
+			nodeToRebalanceParent = next
+
+			*t.parentChild(nodeToDelete) = next
+			next.Parent = nodeToDelete.Parent
+
+			next.Left = nodeToDelete.Left
+			next.Left.Parent = next
+		} else {
+			//         p                 p
+			//         |                 |
+			//      +-----+           +-----+
+			//      | ntd |           | nxt |
+			//      +-----+           +-----+
+			//      /     \           /     \
+			//     a       x         a       x
+			//            / \    =>         / \
+			//           y   z             y   z
+			//          / \               / \
+			//    +-----+  c             b   c
+			//    | nxt |
+			//    +-----+
+			//    /     \
+			//  nil     b
+			y := next.Parent
+			b := next.Right
+			nodeToRebalance = b
+			nodeToRebalanceParent = y
+
+			*t.parentChild(nodeToDelete) = next
+			next.Parent = nodeToDelete.Parent
+
+			next.Left = nodeToDelete.Left
+			next.Left.Parent = next
+
+			next.Right = nodeToDelete.Right
+			next.Right.Parent = next
+
+			y.Left = b
+			if b != nil {
+				b.Parent = y
+			}
+		}
+
+		// idk
+		needsRebalance = next.Color == Black
+		next.Color = nodeToDelete.Color
+	}
+
+	if needsRebalance {
+		node := nodeToRebalance
+		nodeParent := nodeToRebalanceParent
+		for node != t.root && node.getColor() == Black {
+			if node == nodeParent.Left {
+				sibling := nodeParent.Right
+				if sibling.getColor() == Red {
+					sibling.Color = Black
+					nodeParent.Color = Red
+					t.leftRotate(nodeParent)
+					sibling = nodeParent.Right
+				}
+				if sibling.Left.getColor() == Black && sibling.Right.getColor() == Black {
+					sibling.Color = Red
+					node, nodeParent = nodeParent, nodeParent.Parent
+				} else {
+					if sibling.Right.getColor() == Black {
+						sibling.Left.Color = Black
+						sibling.Color = Red
+						t.rightRotate(sibling)
+						sibling = nodeParent.Right
+					}
+					sibling.Color = nodeParent.Color
+					nodeParent.Color = Black
+					sibling.Right.Color = Black
+					t.leftRotate(nodeParent)
+					node, nodeParent = t.root, nil
+				}
+			} else {
+				sibling := nodeParent.Left
+				if sibling.getColor() == Red {
+					sibling.Color = Black
+					nodeParent.Color = Red
+					t.rightRotate(nodeParent)
+					sibling = nodeParent.Left
+				}
+				if sibling.Right.getColor() == Black && sibling.Left.getColor() == Black {
+					sibling.Color = Red
+					node, nodeParent = nodeParent, nodeParent.Parent
+				} else {
+					if sibling.Left.getColor() == Black {
+						sibling.Right.Color = Black
+						sibling.Color = Red
+						t.leftRotate(sibling)
+						sibling = nodeParent.Left
+					}
+					sibling.Color = nodeParent.Color
+					nodeParent.Color = Black
+					sibling.Left.Color = Black
+					t.rightRotate(nodeParent)
+					node, nodeParent = t.root, nil
+				}
+			}
+		}
+		if node != nil {
+			node.Color = Black
+		}
+	}
+}