You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: bintree.go
    path of file: ./repos/octant/vendor/github.com/ulikunitz/xz/lzma
    
    the code of the file until where you have to start completion: // 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 o
    
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
}