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gitea/vendor/github.com/ulikunitz/xz/lzma/bintree.go
2021-02-28 18:08:33 -05:00

523 lines
9.4 KiB
Go
Vendored

// Copyright 2014-2021 Ulrich Kunitz. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package lzma
import (
"errors"
"unicode"
)
// node represents a node in the binary tree.
type node struct {
// x is the search value
x uint32
// p parent node
p uint32
// l left child
l uint32
// r right child
r uint32
}
// wordLen is the number of bytes represented by the v field of a node.
const wordLen = 4
// binTree supports the identification of the next operation based on a
// binary tree.
//
// Nodes will be identified by their index into the ring buffer.
type binTree struct {
dict *encoderDict
// ring buffer of nodes
node []node
// absolute offset of the entry for the next node. Position 4
// byte larger.
hoff int64
// front position in the node ring buffer
front uint32
// index of the root node
root uint32
// current x value
x uint32
// preallocated array
data []byte
}
// null represents the nonexistent index. We can't use zero because it
// would always exist or we would need to decrease the index for each
// reference.
const null uint32 = 1<<32 - 1
// newBinTree initializes the binTree structure. The capacity defines
// the size of the buffer and defines the maximum distance for which
// matches will be found.
func newBinTree(capacity int) (t *binTree, err error) {
if capacity < 1 {
return nil, errors.New(
"newBinTree: capacity must be larger than zero")
}
if int64(capacity) >= int64(null) {
return nil, errors.New(
"newBinTree: capacity must less 2^{32}-1")
}
t = &binTree{
node: make([]node, capacity),
hoff: -int64(wordLen),
root: null,
data: make([]byte, maxMatchLen),
}
return t, nil
}
func (t *binTree) SetDict(d *encoderDict) { t.dict = d }
// WriteByte writes a single byte into the binary tree.
func (t *binTree) WriteByte(c byte) error {
t.x = (t.x << 8) | uint32(c)
t.hoff++
if t.hoff < 0 {
return nil
}
v := t.front
if int64(v) < t.hoff {
// We are overwriting old nodes stored in the tree.
t.remove(v)
}
t.node[v].x = t.x
t.add(v)
t.front++
if int64(t.front) >= int64(len(t.node)) {
t.front = 0
}
return nil
}
// Writes writes a sequence of bytes into the binTree structure.
func (t *binTree) Write(p []byte) (n int, err error) {
for _, c := range p {
t.WriteByte(c)
}
return len(p), nil
}
// add puts the node v into the tree. The node must not be part of the
// tree before.
func (t *binTree) add(v uint32) {
vn := &t.node[v]
// Set left and right to null indices.
vn.l, vn.r = null, null
// If the binary tree is empty make v the root.
if t.root == null {
t.root = v
vn.p = null
return
}
x := vn.x
p := t.root
// Search for the right leave link and add the new node.
for {
pn := &t.node[p]
if x <= pn.x {
if pn.l == null {
pn.l = v
vn.p = p
return
}
p = pn.l
} else {
if pn.r == null {
pn.r = v
vn.p = p
return
}
p = pn.r
}
}
}
// parent returns the parent node index of v and the pointer to v value
// in the parent.
func (t *binTree) parent(v uint32) (p uint32, ptr *uint32) {
if t.root == v {
return null, &t.root
}
p = t.node[v].p
if t.node[p].l == v {
ptr = &t.node[p].l
} else {
ptr = &t.node[p].r
}
return
}
// Remove node v.
func (t *binTree) remove(v uint32) {
vn := &t.node[v]
p, ptr := t.parent(v)
l, r := vn.l, vn.r
if l == null {
// Move the right child up.
*ptr = r
if r != null {
t.node[r].p = p
}
return
}
if r == null {
// Move the left child up.
*ptr = l
t.node[l].p = p
return
}
// Search the in-order predecessor u.
un := &t.node[l]
ur := un.r
if ur == null {
// In order predecessor is l. Move it up.
un.r = r
t.node[r].p = l
un.p = p
*ptr = l
return
}
var u uint32
for {
// Look for the max value in the tree where l is root.
u = ur
ur = t.node[u].r
if ur == null {
break
}
}
// replace u with ul
un = &t.node[u]
ul := un.l
up := un.p
t.node[up].r = ul
if ul != null {
t.node[ul].p = up
}
// replace v by u
un.l, un.r = l, r
t.node[l].p = u
t.node[r].p = u
*ptr = u
un.p = p
}
// search looks for the node that have the value x or for the nodes that
// brace it. The node highest in the tree with the value x will be
// returned. All other nodes with the same value live in left subtree of
// the returned node.
func (t *binTree) search(v uint32, x uint32) (a, b uint32) {
a, b = null, null
if v == null {
return
}
for {
vn := &t.node[v]
if x <= vn.x {
if x == vn.x {
return v, v
}
b = v
if vn.l == null {
return
}
v = vn.l
} else {
a = v
if vn.r == null {
return
}
v = vn.r
}
}
}
// max returns the node with maximum value in the subtree with v as
// root.
func (t *binTree) max(v uint32) uint32 {
if v == null {
return null
}
for {
r := t.node[v].r
if r == null {
return v
}
v = r
}
}
// min returns the node with the minimum value in the subtree with v as
// root.
func (t *binTree) min(v uint32) uint32 {
if v == null {
return null
}
for {
l := t.node[v].l
if l == null {
return v
}
v = l
}
}
// pred returns the in-order predecessor of node v.
func (t *binTree) pred(v uint32) uint32 {
if v == null {
return null
}
u := t.max(t.node[v].l)
if u != null {
return u
}
for {
p := t.node[v].p
if p == null {
return null
}
if t.node[p].r == v {
return p
}
v = p
}
}
// succ returns the in-order successor of node v.
func (t *binTree) succ(v uint32) uint32 {
if v == null {
return null
}
u := t.min(t.node[v].r)
if u != null {
return u
}
for {
p := t.node[v].p
if p == null {
return null
}
if t.node[p].l == v {
return p
}
v = p
}
}
// xval converts the first four bytes of a into an 32-bit unsigned
// integer in big-endian order.
func xval(a []byte) uint32 {
var x uint32
switch len(a) {
default:
x |= uint32(a[3])
fallthrough
case 3:
x |= uint32(a[2]) << 8
fallthrough
case 2:
x |= uint32(a[1]) << 16
fallthrough
case 1:
x |= uint32(a[0]) << 24
case 0:
}
return x
}
// dumpX converts value x into a four-letter string.
func dumpX(x uint32) string {
a := make([]byte, 4)
for i := 0; i < 4; i++ {
c := byte(x >> uint((3-i)*8))
if unicode.IsGraphic(rune(c)) {
a[i] = c
} else {
a[i] = '.'
}
}
return string(a)
}
/*
// dumpNode writes a representation of the node v into the io.Writer.
func (t *binTree) dumpNode(w io.Writer, v uint32, indent int) {
if v == null {
return
}
vn := &t.node[v]
t.dumpNode(w, vn.r, indent+2)
for i := 0; i < indent; i++ {
fmt.Fprint(w, " ")
}
if vn.p == null {
fmt.Fprintf(w, "node %d %q parent null\n", v, dumpX(vn.x))
} else {
fmt.Fprintf(w, "node %d %q parent %d\n", v, dumpX(vn.x), vn.p)
}
t.dumpNode(w, vn.l, indent+2)
}
// dump prints a representation of the binary tree into the writer.
func (t *binTree) dump(w io.Writer) error {
bw := bufio.NewWriter(w)
t.dumpNode(bw, t.root, 0)
return bw.Flush()
}
*/
func (t *binTree) distance(v uint32) int {
dist := int(t.front) - int(v)
if dist <= 0 {
dist += len(t.node)
}
return dist
}
type matchParams struct {
rep [4]uint32
// length when match will be accepted
nAccept int
// nodes to check
check int
// finish if length get shorter
stopShorter bool
}
func (t *binTree) match(m match, distIter func() (int, bool), p matchParams,
) (r match, checked int, accepted bool) {
buf := &t.dict.buf
for {
if checked >= p.check {
return m, checked, true
}
dist, ok := distIter()
if !ok {
return m, checked, false
}
checked++
if m.n > 0 {
i := buf.rear - dist + m.n - 1
if i < 0 {
i += len(buf.data)
} else if i >= len(buf.data) {
i -= len(buf.data)
}
if buf.data[i] != t.data[m.n-1] {
if p.stopShorter {
return m, checked, false
}
continue
}
}
n := buf.matchLen(dist, t.data)
switch n {
case 0:
if p.stopShorter {
return m, checked, false
}
continue
case 1:
if uint32(dist-minDistance) != p.rep[0] {
continue
}
}
if n < m.n || (n == m.n && int64(dist) >= m.distance) {
continue
}
m = match{int64(dist), n}
if n >= p.nAccept {
return m, checked, true
}
}
}
func (t *binTree) NextOp(rep [4]uint32) operation {
// retrieve maxMatchLen data
n, _ := t.dict.buf.Peek(t.data[:maxMatchLen])
if n == 0 {
panic("no data in buffer")
}
t.data = t.data[:n]
var (
m match
x, u, v uint32
iterPred, iterSucc func() (int, bool)
)
p := matchParams{
rep: rep,
nAccept: maxMatchLen,
check: 32,
}
i := 4
iterSmall := func() (dist int, ok bool) {
i--
if i <= 0 {
return 0, false
}
return i, true
}
m, checked, accepted := t.match(m, iterSmall, p)
if accepted {
goto end
}
p.check -= checked
x = xval(t.data)
u, v = t.search(t.root, x)
if u == v && len(t.data) == 4 {
iter := func() (dist int, ok bool) {
if u == null {
return 0, false
}
dist = t.distance(u)
u, v = t.search(t.node[u].l, x)
if u != v {
u = null
}
return dist, true
}
m, _, _ = t.match(m, iter, p)
goto end
}
p.stopShorter = true
iterSucc = func() (dist int, ok bool) {
if v == null {
return 0, false
}
dist = t.distance(v)
v = t.succ(v)
return dist, true
}
m, checked, accepted = t.match(m, iterSucc, p)
if accepted {
goto end
}
p.check -= checked
iterPred = func() (dist int, ok bool) {
if u == null {
return 0, false
}
dist = t.distance(u)
u = t.pred(u)
return dist, true
}
m, _, _ = t.match(m, iterPred, p)
end:
if m.n == 0 {
return lit{t.data[0]}
}
return m
}