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interval_tree.go
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interval_tree.go
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// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package adt
import (
"bytes"
"fmt"
"math"
"strings"
)
// Comparable is an interface for trichotomic comparisons.
type Comparable interface {
// Compare gives the result of a 3-way comparison
// a.Compare(b) = 1 => a > b
// a.Compare(b) = 0 => a == b
// a.Compare(b) = -1 => a < b
Compare(c Comparable) int
}
type rbcolor int
const (
black rbcolor = iota
red
)
func (c rbcolor) String() string {
switch c {
case black:
return "black"
case red:
return "red"
default:
panic(fmt.Errorf("unknown color %d", c))
}
}
// Interval implements a Comparable interval [begin, end)
// TODO: support different sorts of intervals: (a,b), [a,b], (a, b]
type Interval struct {
Begin Comparable
End Comparable
}
// Compare on an interval gives == if the interval overlaps.
func (ivl *Interval) Compare(c Comparable) int {
ivl2 := c.(*Interval)
ivbCmpBegin := ivl.Begin.Compare(ivl2.Begin)
ivbCmpEnd := ivl.Begin.Compare(ivl2.End)
iveCmpBegin := ivl.End.Compare(ivl2.Begin)
// ivl is left of ivl2
if ivbCmpBegin < 0 && iveCmpBegin <= 0 {
return -1
}
// iv is right of iv2
if ivbCmpEnd >= 0 {
return 1
}
return 0
}
type intervalNode struct {
// iv is the interval-value pair entry.
iv IntervalValue
// max endpoint of all descendent nodes.
max Comparable
// left and right are sorted by low endpoint of key interval
left, right *intervalNode
// parent is the direct ancestor of the node
parent *intervalNode
c rbcolor
}
func (x *intervalNode) color(sentinel *intervalNode) rbcolor {
if x == sentinel {
return black
}
return x.c
}
func (x *intervalNode) height(sentinel *intervalNode) int {
if x == sentinel {
return 0
}
ld := x.left.height(sentinel)
rd := x.right.height(sentinel)
if ld < rd {
return rd + 1
}
return ld + 1
}
func (x *intervalNode) min(sentinel *intervalNode) *intervalNode {
for x.left != sentinel {
x = x.left
}
return x
}
// successor is the next in-order node in the tree
func (x *intervalNode) successor(sentinel *intervalNode) *intervalNode {
if x.right != sentinel {
return x.right.min(sentinel)
}
y := x.parent
for y != sentinel && x == y.right {
x = y
y = y.parent
}
return y
}
// updateMax updates the maximum values for a node and its ancestors
func (x *intervalNode) updateMax(sentinel *intervalNode) {
for x != sentinel {
oldmax := x.max
max := x.iv.Ivl.End
if x.left != sentinel && x.left.max.Compare(max) > 0 {
max = x.left.max
}
if x.right != sentinel && x.right.max.Compare(max) > 0 {
max = x.right.max
}
if oldmax.Compare(max) == 0 {
break
}
x.max = max
x = x.parent
}
}
type nodeVisitor func(n *intervalNode) bool
// visit will call a node visitor on each node that overlaps the given interval
func (x *intervalNode) visit(iv *Interval, sentinel *intervalNode, nv nodeVisitor) bool {
if x == sentinel {
return true
}
v := iv.Compare(&x.iv.Ivl)
switch {
case v < 0:
if !x.left.visit(iv, sentinel, nv) {
return false
}
case v > 0:
maxiv := Interval{x.iv.Ivl.Begin, x.max}
if maxiv.Compare(iv) == 0 {
if !x.left.visit(iv, sentinel, nv) || !x.right.visit(iv, sentinel, nv) {
return false
}
}
default:
if !x.left.visit(iv, sentinel, nv) || !nv(x) || !x.right.visit(iv, sentinel, nv) {
return false
}
}
return true
}
// IntervalValue represents a range tree node that contains a range and a value.
type IntervalValue struct {
Ivl Interval
Val interface{}
}
// IntervalTree represents a (mostly) textbook implementation of the
// "Introduction to Algorithms" (Cormen et al, 3rd ed.) chapter 13 red-black tree
// and chapter 14.3 interval tree with search supporting "stabbing queries".
type IntervalTree interface {
// Insert adds a node with the given interval into the tree.
Insert(ivl Interval, val interface{})
// Delete removes the node with the given interval from the tree, returning
// true if a node is in fact removed.
Delete(ivl Interval) bool
// Len gives the number of elements in the tree.
Len() int
// Height is the number of levels in the tree; one node has height 1.
Height() int
// MaxHeight is the expected maximum tree height given the number of nodes.
MaxHeight() int
// Visit calls a visitor function on every tree node intersecting the given interval.
// It will visit each interval [x, y) in ascending order sorted on x.
Visit(ivl Interval, ivv IntervalVisitor)
// Find gets the IntervalValue for the node matching the given interval
Find(ivl Interval) *IntervalValue
// Intersects returns true if there is some tree node intersecting the given interval.
Intersects(iv Interval) bool
// Contains returns true if the interval tree's keys cover the entire given interval.
Contains(ivl Interval) bool
// Stab returns a slice with all elements in the tree intersecting the interval.
Stab(iv Interval) []*IntervalValue
// Union merges a given interval tree into the receiver.
Union(inIvt IntervalTree, ivl Interval)
}
// NewIntervalTree returns a new interval tree.
func NewIntervalTree() IntervalTree {
sentinel := &intervalNode{
iv: IntervalValue{},
max: nil,
left: nil,
right: nil,
parent: nil,
c: black,
}
return &intervalTree{
root: sentinel,
count: 0,
sentinel: sentinel,
}
}
type intervalTree struct {
root *intervalNode
count int
// red-black NIL node
// use 'sentinel' as a dummy object to simplify boundary conditions
// use the sentinel to treat a nil child of a node x as an ordinary node whose parent is x
// use one shared sentinel to represent all nil leaves and the root's parent
sentinel *intervalNode
}
// TODO: make this consistent with textbook implementation
//
// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.4, p324
//
// 0. RB-DELETE(T, z)
// 1.
// 2. y = z
// 3. y-original-color = y.color
// 4.
// 5. if z.left == T.nil
// 6. x = z.right
// 7. RB-TRANSPLANT(T, z, z.right)
// 8. else if z.right == T.nil
// 9. x = z.left
// 10. RB-TRANSPLANT(T, z, z.left)
// 11. else
// 12. y = TREE-MINIMUM(z.right)
// 13. y-original-color = y.color
// 14. x = y.right
// 15. if y.p == z
// 16. x.p = y
// 17. else
// 18. RB-TRANSPLANT(T, y, y.right)
// 19. y.right = z.right
// 20. y.right.p = y
// 21. RB-TRANSPLANT(T, z, y)
// 22. y.left = z.left
// 23. y.left.p = y
// 24. y.color = z.color
// 25.
// 26. if y-original-color == BLACK
// 27. RB-DELETE-FIXUP(T, x)
// Delete removes the node with the given interval from the tree, returning
// true if a node is in fact removed.
func (ivt *intervalTree) Delete(ivl Interval) bool {
z := ivt.find(ivl)
if z == ivt.sentinel {
return false
}
y := z
if z.left != ivt.sentinel && z.right != ivt.sentinel {
y = z.successor(ivt.sentinel)
}
x := ivt.sentinel
if y.left != ivt.sentinel {
x = y.left
} else if y.right != ivt.sentinel {
x = y.right
}
x.parent = y.parent
if y.parent == ivt.sentinel {
ivt.root = x
} else {
if y == y.parent.left {
y.parent.left = x
} else {
y.parent.right = x
}
y.parent.updateMax(ivt.sentinel)
}
if y != z {
z.iv = y.iv
z.updateMax(ivt.sentinel)
}
if y.color(ivt.sentinel) == black {
ivt.deleteFixup(x)
}
ivt.count--
return true
}
// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.4, p326
//
// 0. RB-DELETE-FIXUP(T, z)
// 1.
// 2. while x ≠ T.root and x.color == BLACK
// 3. if x == x.p.left
// 4. w = x.p.right
// 5. if w.color == RED
// 6. w.color = BLACK
// 7. x.p.color = RED
// 8. LEFT-ROTATE(T, x, p)
// 9. if w.left.color == BLACK and w.right.color == BLACK
// 10. w.color = RED
// 11. x = x.p
// 12. else if w.right.color == BLACK
// 13. w.left.color = BLACK
// 14. w.color = RED
// 15. RIGHT-ROTATE(T, w)
// 16. w = w.p.right
// 17. w.color = x.p.color
// 18. x.p.color = BLACK
// 19. LEFT-ROTATE(T, w.p)
// 20. x = T.root
// 21. else
// 22. w = x.p.left
// 23. if w.color == RED
// 24. w.color = BLACK
// 25. x.p.color = RED
// 26. RIGHT-ROTATE(T, x, p)
// 27. if w.right.color == BLACK and w.left.color == BLACK
// 28. w.color = RED
// 29. x = x.p
// 30. else if w.left.color == BLACK
// 31. w.right.color = BLACK
// 32. w.color = RED
// 33. LEFT-ROTATE(T, w)
// 34. w = w.p.left
// 35. w.color = x.p.color
// 36. x.p.color = BLACK
// 37. RIGHT-ROTATE(T, w.p)
// 38. x = T.root
// 39.
// 40. x.color = BLACK
//
func (ivt *intervalTree) deleteFixup(x *intervalNode) {
for x != ivt.root && x.color(ivt.sentinel) == black {
if x == x.parent.left { // line 3-20
w := x.parent.right
if w.color(ivt.sentinel) == red {
w.c = black
x.parent.c = red
ivt.rotateLeft(x.parent)
w = x.parent.right
}
if w == nil {
break
}
if w.left.color(ivt.sentinel) == black && w.right.color(ivt.sentinel) == black {
w.c = red
x = x.parent
} else {
if w.right.color(ivt.sentinel) == black {
w.left.c = black
w.c = red
ivt.rotateRight(w)
w = x.parent.right
}
w.c = x.parent.color(ivt.sentinel)
x.parent.c = black
w.right.c = black
ivt.rotateLeft(x.parent)
x = ivt.root
}
} else { // line 22-38
// same as above but with left and right exchanged
w := x.parent.left
if w.color(ivt.sentinel) == red {
w.c = black
x.parent.c = red
ivt.rotateRight(x.parent)
w = x.parent.left
}
if w == nil {
break
}
if w.left.color(ivt.sentinel) == black && w.right.color(ivt.sentinel) == black {
w.c = red
x = x.parent
} else {
if w.left.color(ivt.sentinel) == black {
w.right.c = black
w.c = red
ivt.rotateLeft(w)
w = x.parent.left
}
w.c = x.parent.color(ivt.sentinel)
x.parent.c = black
w.left.c = black
ivt.rotateRight(x.parent)
x = ivt.root
}
}
}
if x != nil {
x.c = black
}
}
func (ivt *intervalTree) createIntervalNode(ivl Interval, val interface{}) *intervalNode {
return &intervalNode{
iv: IntervalValue{ivl, val},
max: ivl.End,
c: red,
left: ivt.sentinel,
right: ivt.sentinel,
parent: ivt.sentinel,
}
}
// TODO: make this consistent with textbook implementation
//
// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.3, p315
//
// 0. RB-INSERT(T, z)
// 1.
// 2. y = T.nil
// 3. x = T.root
// 4.
// 5. while x ≠ T.nil
// 6. y = x
// 7. if z.key < x.key
// 8. x = x.left
// 9. else
// 10. x = x.right
// 11.
// 12. z.p = y
// 13.
// 14. if y == T.nil
// 15. T.root = z
// 16. else if z.key < y.key
// 17. y.left = z
// 18. else
// 19. y.right = z
// 20.
// 21. z.left = T.nil
// 22. z.right = T.nil
// 23. z.color = RED
// 24.
// 25. RB-INSERT-FIXUP(T, z)
// Insert adds a node with the given interval into the tree.
func (ivt *intervalTree) Insert(ivl Interval, val interface{}) {
y := ivt.sentinel
z := ivt.createIntervalNode(ivl, val)
x := ivt.root
for x != ivt.sentinel {
y = x
if z.iv.Ivl.Begin.Compare(x.iv.Ivl.Begin) < 0 {
x = x.left
} else {
x = x.right
}
}
z.parent = y
if y == ivt.sentinel {
ivt.root = z
} else {
if z.iv.Ivl.Begin.Compare(y.iv.Ivl.Begin) < 0 {
y.left = z
} else {
y.right = z
}
y.updateMax(ivt.sentinel)
}
z.c = red
ivt.insertFixup(z)
ivt.count++
}
// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.3, p316
//
// 0. RB-INSERT-FIXUP(T, z)
// 1.
// 2. while z.p.color == RED
// 3. if z.p == z.p.p.left
// 4. y = z.p.p.right
// 5. if y.color == RED
// 6. z.p.color = BLACK
// 7. y.color = BLACK
// 8. z.p.p.color = RED
// 9. z = z.p.p
// 10. else if z == z.p.right
// 11. z = z.p
// 12. LEFT-ROTATE(T, z)
// 13. z.p.color = BLACK
// 14. z.p.p.color = RED
// 15. RIGHT-ROTATE(T, z.p.p)
// 16. else
// 17. y = z.p.p.left
// 18. if y.color == RED
// 19. z.p.color = BLACK
// 20. y.color = BLACK
// 21. z.p.p.color = RED
// 22. z = z.p.p
// 23. else if z == z.p.right
// 24. z = z.p
// 25. RIGHT-ROTATE(T, z)
// 26. z.p.color = BLACK
// 27. z.p.p.color = RED
// 28. LEFT-ROTATE(T, z.p.p)
// 29.
// 30. T.root.color = BLACK
//
func (ivt *intervalTree) insertFixup(z *intervalNode) {
for z.parent.color(ivt.sentinel) == red {
if z.parent == z.parent.parent.left { // line 3-15
y := z.parent.parent.right
if y.color(ivt.sentinel) == red {
y.c = black
z.parent.c = black
z.parent.parent.c = red
z = z.parent.parent
} else {
if z == z.parent.right {
z = z.parent
ivt.rotateLeft(z)
}
z.parent.c = black
z.parent.parent.c = red
ivt.rotateRight(z.parent.parent)
}
} else { // line 16-28
// same as then with left/right exchanged
y := z.parent.parent.left
if y.color(ivt.sentinel) == red {
y.c = black
z.parent.c = black
z.parent.parent.c = red
z = z.parent.parent
} else {
if z == z.parent.left {
z = z.parent
ivt.rotateRight(z)
}
z.parent.c = black
z.parent.parent.c = red
ivt.rotateLeft(z.parent.parent)
}
}
}
// line 30
ivt.root.c = black
}
// rotateLeft moves x so it is left of its right child
//
// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.2, p313
//
// 0. LEFT-ROTATE(T, x)
// 1.
// 2. y = x.right
// 3. x.right = y.left
// 4.
// 5. if y.left ≠ T.nil
// 6. y.left.p = x
// 7.
// 8. y.p = x.p
// 9.
// 10. if x.p == T.nil
// 11. T.root = y
// 12. else if x == x.p.left
// 13. x.p.left = y
// 14. else
// 15. x.p.right = y
// 16.
// 17. y.left = x
// 18. x.p = y
//
func (ivt *intervalTree) rotateLeft(x *intervalNode) {
// rotateLeft x must have right child
if x.right == ivt.sentinel {
return
}
// line 2-3
y := x.right
x.right = y.left
// line 5-6
if y.left != ivt.sentinel {
y.left.parent = x
}
x.updateMax(ivt.sentinel)
// line 10-15, 18
ivt.replaceParent(x, y)
// line 17
y.left = x
y.updateMax(ivt.sentinel)
}
// rotateRight moves x so it is right of its left child
//
// 0. RIGHT-ROTATE(T, x)
// 1.
// 2. y = x.left
// 3. x.left = y.right
// 4.
// 5. if y.right ≠ T.nil
// 6. y.right.p = x
// 7.
// 8. y.p = x.p
// 9.
// 10. if x.p == T.nil
// 11. T.root = y
// 12. else if x == x.p.right
// 13. x.p.right = y
// 14. else
// 15. x.p.left = y
// 16.
// 17. y.right = x
// 18. x.p = y
//
func (ivt *intervalTree) rotateRight(x *intervalNode) {
// rotateRight x must have left child
if x.left == ivt.sentinel {
return
}
// line 2-3
y := x.left
x.left = y.right
// line 5-6
if y.right != ivt.sentinel {
y.right.parent = x
}
x.updateMax(ivt.sentinel)
// line 10-15, 18
ivt.replaceParent(x, y)
// line 17
y.right = x
y.updateMax(ivt.sentinel)
}
// replaceParent replaces x's parent with y
func (ivt *intervalTree) replaceParent(x *intervalNode, y *intervalNode) {
y.parent = x.parent
if x.parent == ivt.sentinel {
ivt.root = y
} else {
if x == x.parent.left {
x.parent.left = y
} else {
x.parent.right = y
}
x.parent.updateMax(ivt.sentinel)
}
x.parent = y
}
// Len gives the number of elements in the tree
func (ivt *intervalTree) Len() int { return ivt.count }
// Height is the number of levels in the tree; one node has height 1.
func (ivt *intervalTree) Height() int { return ivt.root.height(ivt.sentinel) }
// MaxHeight is the expected maximum tree height given the number of nodes
func (ivt *intervalTree) MaxHeight() int {
return int((2 * math.Log2(float64(ivt.Len()+1))) + 0.5)
}
// IntervalVisitor is used on tree searches; return false to stop searching.
type IntervalVisitor func(n *IntervalValue) bool
// Visit calls a visitor function on every tree node intersecting the given interval.
// It will visit each interval [x, y) in ascending order sorted on x.
func (ivt *intervalTree) Visit(ivl Interval, ivv IntervalVisitor) {
ivt.root.visit(&ivl, ivt.sentinel, func(n *intervalNode) bool { return ivv(&n.iv) })
}
// find the exact node for a given interval
func (ivt *intervalTree) find(ivl Interval) *intervalNode {
ret := ivt.sentinel
f := func(n *intervalNode) bool {
if n.iv.Ivl != ivl {
return true
}
ret = n
return false
}
ivt.root.visit(&ivl, ivt.sentinel, f)
return ret
}
// Find gets the IntervalValue for the node matching the given interval
func (ivt *intervalTree) Find(ivl Interval) (ret *IntervalValue) {
n := ivt.find(ivl)
if n == ivt.sentinel {
return nil
}
return &n.iv
}
// Intersects returns true if there is some tree node intersecting the given interval.
func (ivt *intervalTree) Intersects(iv Interval) bool {
x := ivt.root
for x != ivt.sentinel && iv.Compare(&x.iv.Ivl) != 0 {
if x.left != ivt.sentinel && x.left.max.Compare(iv.Begin) > 0 {
x = x.left
} else {
x = x.right
}
}
return x != ivt.sentinel
}
// Contains returns true if the interval tree's keys cover the entire given interval.
func (ivt *intervalTree) Contains(ivl Interval) bool {
var maxEnd, minBegin Comparable
isContiguous := true
ivt.Visit(ivl, func(n *IntervalValue) bool {
if minBegin == nil {
minBegin = n.Ivl.Begin
maxEnd = n.Ivl.End
return true
}
if maxEnd.Compare(n.Ivl.Begin) < 0 {
isContiguous = false
return false
}
if n.Ivl.End.Compare(maxEnd) > 0 {
maxEnd = n.Ivl.End
}
return true
})
return isContiguous && minBegin != nil && maxEnd.Compare(ivl.End) >= 0 && minBegin.Compare(ivl.Begin) <= 0
}
// Stab returns a slice with all elements in the tree intersecting the interval.
func (ivt *intervalTree) Stab(iv Interval) (ivs []*IntervalValue) {
if ivt.count == 0 {
return nil
}
f := func(n *IntervalValue) bool { ivs = append(ivs, n); return true }
ivt.Visit(iv, f)
return ivs
}
// Union merges a given interval tree into the receiver.
func (ivt *intervalTree) Union(inIvt IntervalTree, ivl Interval) {
f := func(n *IntervalValue) bool {
ivt.Insert(n.Ivl, n.Val)
return true
}
inIvt.Visit(ivl, f)
}
type visitedInterval struct {
root Interval
left Interval
right Interval
color rbcolor
depth int
}
func (vi visitedInterval) String() string {
bd := new(strings.Builder)
bd.WriteString(fmt.Sprintf("root [%v,%v,%v], left [%v,%v], right [%v,%v], depth %d",
vi.root.Begin, vi.root.End, vi.color,
vi.left.Begin, vi.left.End,
vi.right.Begin, vi.right.End,
vi.depth,
))
return bd.String()
}
// visitLevel traverses tree in level order.
// used for testing
func (ivt *intervalTree) visitLevel() []visitedInterval {
if ivt.root == ivt.sentinel {
return nil
}
rs := make([]visitedInterval, 0, ivt.Len())
type pair struct {
node *intervalNode
depth int
}
queue := []pair{{ivt.root, 0}}
for len(queue) > 0 {
f := queue[0]
queue = queue[1:]
vi := visitedInterval{
root: f.node.iv.Ivl,
color: f.node.color(ivt.sentinel),
depth: f.depth,
}
if f.node.left != ivt.sentinel {
vi.left = f.node.left.iv.Ivl
queue = append(queue, pair{f.node.left, f.depth + 1})
}
if f.node.right != ivt.sentinel {
vi.right = f.node.right.iv.Ivl
queue = append(queue, pair{f.node.right, f.depth + 1})
}
rs = append(rs, vi)
}
return rs
}
type StringComparable string
func (s StringComparable) Compare(c Comparable) int {
sc := c.(StringComparable)
if s < sc {
return -1
}
if s > sc {
return 1
}
return 0
}
func NewStringInterval(begin, end string) Interval {
return Interval{StringComparable(begin), StringComparable(end)}
}
func NewStringPoint(s string) Interval {
return Interval{StringComparable(s), StringComparable(s + "\x00")}
}
// StringAffineComparable treats "" as > all other strings
type StringAffineComparable string
func (s StringAffineComparable) Compare(c Comparable) int {
sc := c.(StringAffineComparable)
if len(s) == 0 {
if len(sc) == 0 {
return 0
}
return 1
}
if len(sc) == 0 {
return -1
}
if s < sc {
return -1
}
if s > sc {
return 1
}
return 0
}
func NewStringAffineInterval(begin, end string) Interval {
return Interval{StringAffineComparable(begin), StringAffineComparable(end)}
}
func NewStringAffinePoint(s string) Interval {
return NewStringAffineInterval(s, s+"\x00")
}
func NewInt64Interval(a int64, b int64) Interval {
return Interval{Int64Comparable(a), Int64Comparable(b)}
}
func newInt64EmptyInterval() Interval {
return Interval{Begin: nil, End: nil}
}
func NewInt64Point(a int64) Interval {
return Interval{Int64Comparable(a), Int64Comparable(a + 1)}
}
type Int64Comparable int64
func (v Int64Comparable) Compare(c Comparable) int {
vc := c.(Int64Comparable)
cmp := v - vc
if cmp < 0 {
return -1
}
if cmp > 0 {
return 1
}
return 0
}
// BytesAffineComparable treats empty byte arrays as > all other byte arrays
type BytesAffineComparable []byte
func (b BytesAffineComparable) Compare(c Comparable) int {
bc := c.(BytesAffineComparable)
if len(b) == 0 {
if len(bc) == 0 {
return 0
}
return 1
}
if len(bc) == 0 {
return -1
}
return bytes.Compare(b, bc)
}
func NewBytesAffineInterval(begin, end []byte) Interval {
return Interval{BytesAffineComparable(begin), BytesAffineComparable(end)}
}
func NewBytesAffinePoint(b []byte) Interval {
be := make([]byte, len(b)+1)
copy(be, b)
be[len(b)] = 0
return NewBytesAffineInterval(b, be)
}