134 lines
3.1 KiB
Go
134 lines
3.1 KiB
Go
// Copyright 2013 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package diff implements a linewise diff algorithm.
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package diff
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import (
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"bytes"
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"fmt"
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"strings"
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)
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// Chunk represents a piece of the diff. A chunk will not have both added and
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// deleted lines. Equal lines are always after any added or deleted lines.
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// A Chunk may or may not have any lines in it, especially for the first or last
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// chunk in a computation.
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type Chunk struct {
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Added []string
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Deleted []string
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Equal []string
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}
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// Diff returns a string containing a line-by-line unified diff of the linewise
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// changes required to make A into B. Each line is prefixed with '+', '-', or
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// ' ' to indicate if it should be added, removed, or is correct respectively.
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func Diff(A, B string) string {
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aLines := strings.Split(A, "\n")
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bLines := strings.Split(B, "\n")
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chunks := DiffChunks(aLines, bLines)
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buf := new(bytes.Buffer)
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for _, c := range chunks {
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for _, line := range c.Added {
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fmt.Fprintf(buf, "+%s\n", line)
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}
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for _, line := range c.Deleted {
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fmt.Fprintf(buf, "-%s\n", line)
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}
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for _, line := range c.Equal {
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fmt.Fprintf(buf, " %s\n", line)
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}
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}
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return strings.TrimRight(buf.String(), "\n")
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}
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// DiffChunks uses an O(D(N+M)) shortest-edit-script algorithm
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// to compute the edits required from A to B and returns the
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// edit chunks.
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func DiffChunks(A, B []string) []Chunk {
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// algorithm: http://www.xmailserver.org/diff2.pdf
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N, M := len(A), len(B)
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MAX := N + M
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V := make([]int, 2*MAX+1)
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Vs := make([][]int, 0, 8)
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var D int
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dLoop:
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for D = 0; D <= MAX; D++ {
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for k := -D; k <= D; k += 2 {
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var x int
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if k == -D || (k != D && V[MAX+k-1] < V[MAX+k+1]) {
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x = V[MAX+k+1]
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} else {
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x = V[MAX+k-1] + 1
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}
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y := x - k
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for x < N && y < M && A[x] == B[y] {
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x++
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y++
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}
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V[MAX+k] = x
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if x >= N && y >= M {
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Vs = append(Vs, append(make([]int, 0, len(V)), V...))
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break dLoop
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}
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}
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Vs = append(Vs, append(make([]int, 0, len(V)), V...))
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}
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if D == 0 {
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return nil
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}
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chunks := make([]Chunk, D+1)
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x, y := N, M
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for d := D; d > 0; d-- {
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V := Vs[d]
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k := x - y
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insert := k == -d || (k != d && V[MAX+k-1] < V[MAX+k+1])
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x1 := V[MAX+k]
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var x0, xM, kk int
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if insert {
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kk = k + 1
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x0 = V[MAX+kk]
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xM = x0
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} else {
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kk = k - 1
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x0 = V[MAX+kk]
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xM = x0 + 1
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}
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y0 := x0 - kk
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var c Chunk
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if insert {
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c.Added = B[y0:][:1]
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} else {
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c.Deleted = A[x0:][:1]
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}
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if xM < x1 {
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c.Equal = A[xM:][:x1-xM]
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}
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x, y = x0, y0
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chunks[d] = c
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}
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if x > 0 {
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chunks[0].Equal = A[:x]
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}
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return chunks
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}
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