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: diff.go
    path of file: ./repos/buildkit/vendor/github.com/kylelemons/godebug/diff
    
    the code of the file until where you have to start completion: // Copyright 2013 Google Inc.  All rights reserved.
//
// 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 diff implements a linewise diff algorithm.
package diff

import (
	"bytes"
	"fmt"
	"strings"
)

// Chunk represents a piece of the diff.  A chunk will not have both added and
// deleted lines.  Equal lines are always after any added or deleted lines.
// A Chunk may or may not have any lines in it, especially for the first or last
// chunk in a computation.
type Chunk struct {
	Added   []string
	Deleted []string
	Equal   []string
}

func (c *Chunk) empty() bool {
	return len(c.Added) == 0 && len(c.Deleted) == 0 && len(c.Equal) == 0
}

// Diff returns a string containing a line-by-line unified diff of the linewise
// changes required to make A into B.  Each line is prefixed with '+', '-', or
// ' ' to indicate if it should be added, removed, or is correct respectively.
func Diff(A, B string) string {
	aLines := strings.Split(A, "\n")
	bLines := strings.Split(B, "\n")

	chunks := DiffChunks(aLines, bLines)

	buf := new(bytes.Buffer)
	for _, c := range chunks {
		for _, line := range c.Added {
			fmt.Fprintf(buf, "+%s\n", line)
		}
		for _, line := range c.Deleted {
			fmt.Fprintf(buf, "-%s\n", line)
		}
		for _, line := range c.Equal {
			fmt.Fprintf(buf, " %s\n", line)
		}
	}
	return strings.TrimRight(buf.String(), "\n")
}

// DiffChunks uses an O(D(N+M)) shortest-edit-script algorithm
// to compute the edits required from A to B and returns the
// edit chunks.
func DiffChunks(a, b []string) []Chunk {
	// algorithm: http://www.xmailserver.org/diff2.pdf

	// We'll need these quantities a lot.
	alen, blen := len(a), len(b) // M, N

	// At most, it will require len(a) deletions and len(b) additions
	// to transform a into b.
	maxPath := alen + blen // MAX
	if maxPath == 0 {
		// degenerate case: two empty lists are the same
		return nil
	}

	// Store the endpoint of the path for diagonals.
	// We store only the a index, because the b index on any diagonal
	// (which we know during the loop below) is aidx-diag.
	// endpoint[maxPath] repr
    
func DiffChunks(a, b []string) []Chunk {
	// algorithm: http://www.xmailserver.org/diff2.pdf

	// We'll need these quantities a lot.
	alen, blen := len(a), len(b) // M, N

	// At most, it will require len(a) deletions and len(b) additions
	// to transform a into b.
	maxPath := alen + blen // MAX
	if maxPath == 0 {
		// degenerate case: two empty lists are the same
		return nil
	}

	// Store the endpoint of the path for diagonals.
	// We store only the a index, because the b index on any diagonal
	// (which we know during the loop below) is aidx-diag.
	// endpoint[maxPath] represents the 0 diagonal.
	//
	// Stated differently:
	// endpoint[d] contains the aidx of a furthest reaching path in diagonal d
	endpoint := make([]int, 2*maxPath+1) // V

	saved := make([][]int, 0, 8) // Vs
	save := func() {
		dup := make([]int, len(endpoint))
		copy(dup, endpoint)
		saved = append(saved, dup)
	}

	var editDistance int // D
dLoop:
	for editDistance = 0; editDistance <= maxPath; editDistance++ {
		// The 0 diag(onal) represents equality of a and b.  Each diagonal to
		// the left is numbered one lower, to the right is one higher, from
		// -alen to +blen.  Negative diagonals favor differences from a,
		// positive diagonals favor differences from b.  The edit distance to a
		// diagonal d cannot be shorter than d itself.
		//
		// The iterations of this loop cover either odds or evens, but not both,
		// If odd indices are inputs, even indices are outputs and vice versa.
		for diag := -editDistance; diag <= editDistance; diag += 2 { // k
			var aidx int // x
			switch {
			case diag == -editDistance:
				// This is a new diagonal; copy from previous iter
				aidx = endpoint[maxPath-editDistance+1] + 0
			case diag == editDistance:
				// This is a new diagonal; copy from previous iter
				aidx = endpoint[maxPath+editDistance-1] + 1
			case endpoint[maxPath+diag+1] > endpoint[maxPath+diag-1]:
				// diagonal d+1 was farther along, so use that
				aidx = endpoint[maxPath+diag+1] + 0
			default:
				// diagonal d-1 was farther (or the same), so use that
				aidx = endpoint[maxPath+diag-1] + 1
			}
			// On diagonal d, we can compute bidx from aidx.
			bidx := aidx - diag // y
			// See how far we can go on this diagonal before we find a difference.
			for aidx < alen && bidx < blen && a[aidx] == b[bidx] {
				aidx++
				bidx++
			}
			// Store the end of the current edit chain.
			endpoint[maxPath+diag] = aidx
			// If we've found the end of both inputs, we're done!
			if aidx >= alen && bidx >= blen {
				save() // save the final path
				break dLoop
			}
		}
		save() // save the current path
	}
	if editDistance == 0 {
		return nil
	}
	chunks := make([]Chunk, editDistance+1)

	x, y := alen, blen
	for d := editDistance; d > 0; d-- {
		endpoint := saved[d]
		diag := x - y
		insert := diag == -d || (diag != d && endpoint[maxPath+diag-1] < endpoint[maxPath+diag+1])

		x1 := endpoint[maxPath+diag]
		var x0, xM, kk int
		if insert {
			kk = diag + 1
			x0 = endpoint[maxPath+kk]
			xM = x0
		} else {
			kk = diag - 1
			x0 = endpoint[maxPath+kk]
			xM = x0 + 1
		}
		y0 := x0 - kk

		var c Chunk
		if insert {
			c.Added = b[y0:][:1]
		} else {
			c.Deleted = a[x0:][:1]
		}
		if xM < x1 {
			c.Equal = a[xM:][:x1-xM]
		}

		x, y = x0, y0
		chunks[d] = c
	}
	if x > 0 {
		chunks[0].Equal = a[:x]
	}
	if chunks[0].empty() {
		chunks = chunks[1:]
	}
	if len(chunks) == 0 {
		return nil
	}
	return chunks
}