diff.java

来自「JAVA 语言的函数式编程扩展」· Java 代码 · 共 875 行 · 第 1/2 页

// $Id$

package scala.tools.partest.nest;

import java.util.Hashtable;

/** A class to compare vectors of objects.  The result of comparison
    is a list of <code>change</code> objects which form an
    edit script.  The objects compared are traditionally lines
    of text from two files.  Comparison options such as "ignore
    whitespace" are implemented by modifying the <code>equals</code>
    and <code>hashcode</code> methods for the objects compared.
<p>
   The basic algorithm is described in: </br>
   "An O(ND) Difference Algorithm and its Variations", Eugene Myers,
   Algorithmica Vol. 1 No. 2, 1986, p 251.  
<p>
   This class outputs different results from GNU diff 1.15 on some
   inputs.  Our results are actually better (smaller change list, smaller
   total size of changes), but it would be nice to know why.  Perhaps
   there is a memory overwrite bug in GNU diff 1.15.

  @author Stuart D. Gathman, translated from GNU diff 1.15
    Copyright (C) 2000  Business Management Systems, Inc.
<p>
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 1, or (at your option)
    any later version.
<p>
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
<p>
    You should have received a copy of the <a href=COPYING.txt>
    GNU General Public License</a>
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 */

public class Diff {

  /** Prepare to find differences between two arrays.  Each element of
      the arrays is translated to an "equivalence number" based on
      the result of <code>equals</code>.  The original Object arrays
      are no longer needed for computing the differences.  They will
      be needed again later to print the results of the comparison as
      an edit script, if desired.
   */
  public Diff(Object[] a,Object[] b) {
    Hashtable h = new Hashtable(a.length + b.length);
    filevec[0] = new file_data(a,h);
    filevec[1] = new file_data(b,h);
  }

  /** 1 more than the maximum equivalence value used for this or its
     sibling file. */
  private int equiv_max = 1;

  /** When set to true, the comparison uses a heuristic to speed it up.
    With this heuristic, for files with a constant small density
    of changes, the algorithm is linear in the file size.  */
  public boolean heuristic = false;

  /** When set to true, the algorithm returns a guarranteed minimal
      set of changes.  This makes things slower, sometimes much slower. */
  public boolean no_discards = false;

  private int[] xvec, yvec;	/* Vectors being compared. */
  private int[] fdiag;		/* Vector, indexed by diagonal, containing
				   the X coordinate of the point furthest
				   along the given diagonal in the forward
				   search of the edit matrix. */
  private int[] bdiag;		/* Vector, indexed by diagonal, containing
				   the X coordinate of the point furthest
				   along the given diagonal in the backward
				   search of the edit matrix. */
  private int fdiagoff, bdiagoff;
  private final file_data[] filevec = new file_data[2];
  private int cost;

  /** Find the midpoint of the shortest edit script for a specified
     portion of the two files.

     We scan from the beginnings of the files, and simultaneously from the ends,
     doing a breadth-first search through the space of edit-sequence.
     When the two searches meet, we have found the midpoint of the shortest
     edit sequence.

     The value returned is the number of the diagonal on which the midpoint lies.
     The diagonal number equals the number of inserted lines minus the number
     of deleted lines (counting only lines before the midpoint).
     The edit cost is stored into COST; this is the total number of
     lines inserted or deleted (counting only lines before the midpoint).

     This function assumes that the first lines of the specified portions
     of the two files do not match, and likewise that the last lines do not
     match.  The caller must trim matching lines from the beginning and end
     of the portions it is going to specify.

     Note that if we return the "wrong" diagonal value, or if
     the value of bdiag at that diagonal is "wrong",
     the worst this can do is cause suboptimal diff output.
     It cannot cause incorrect diff output.  */

  private int diag (int xoff, int xlim, int yoff, int ylim) {
    final int[] fd = fdiag;	// Give the compiler a chance.
    final int[] bd = bdiag;	// Additional help for the compiler.
    final int[] xv = xvec;		// Still more help for the compiler.
    final int[] yv = yvec;		// And more and more . . .
    final int dmin = xoff - ylim;	// Minimum valid diagonal.
    final int dmax = xlim - yoff;	// Maximum valid diagonal.
    final int fmid = xoff - yoff;	// Center diagonal of top-down search.
    final int bmid = xlim - ylim;	// Center diagonal of bottom-up search.
    int fmin = fmid, fmax = fmid;	// Limits of top-down search.
    int bmin = bmid, bmax = bmid;	// Limits of bottom-up search.
    /* True if southeast corner is on an odd
				     diagonal with respect to the northwest. */
    final boolean odd = (fmid - bmid & 1) != 0;	

    fd[fdiagoff + fmid] = xoff;
    bd[bdiagoff + bmid] = xlim;

    for (int c = 1;; ++c)
      {
	int d;			/* Active diagonal. */
	boolean big_snake = false;

	/* Extend the top-down search by an edit step in each diagonal. */
	if (fmin > dmin)
	  fd[fdiagoff + --fmin - 1] = -1;
	else
	  ++fmin;
	if (fmax < dmax)
	  fd[fdiagoff + ++fmax + 1] = -1;
	else
	  --fmax;
	for (d = fmax; d >= fmin; d -= 2)
	  {
	    int x, y, oldx, tlo = fd[fdiagoff + d - 1], thi = fd[fdiagoff + d + 1];

	    if (tlo >= thi)
	      x = tlo + 1;
	    else
	      x = thi;
	    oldx = x;
	    y = x - d;
	    while (x < xlim && y < ylim && xv[x] == yv[y]) {
	      ++x; ++y;
	    }
	    if (x - oldx > 20)
	      big_snake = true;
	    fd[fdiagoff + d] = x;
	    if (odd && bmin <= d && d <= bmax && bd[bdiagoff + d] <= fd[fdiagoff + d])
	      {
		cost = 2 * c - 1;
		return d;
	      }
	  }

	/* Similar extend the bottom-up search. */
	if (bmin > dmin)
	  bd[bdiagoff + --bmin - 1] = Integer.MAX_VALUE;
	else
	  ++bmin;
	if (bmax < dmax)
	  bd[bdiagoff + ++bmax + 1] = Integer.MAX_VALUE;
	else
	  --bmax;
	for (d = bmax; d >= bmin; d -= 2)
	  {
	    int x, y, oldx, tlo = bd[bdiagoff + d - 1], thi = bd[bdiagoff + d + 1];

	    if (tlo < thi)
	      x = tlo;
	    else
	      x = thi - 1;
	    oldx = x;
	    y = x - d;
	    while (x > xoff && y > yoff && xv[x - 1] == yv[y - 1]) {
	      --x; --y;
	    }
	    if (oldx - x > 20)
	      big_snake = true;
	    bd[bdiagoff + d] = x;
	    if (!odd && fmin <= d && d <= fmax && bd[bdiagoff + d] <= fd[fdiagoff + d])
	      {
		cost = 2 * c;
		return d;
	      }
	  }

	/* Heuristic: check occasionally for a diagonal that has made
	   lots of progress compared with the edit distance.
	   If we have any such, find the one that has made the most
	   progress and return it as if it had succeeded.

	   With this heuristic, for files with a constant small density
	   of changes, the algorithm is linear in the file size.  */

	if (c > 200 && big_snake && heuristic)
	  {
	    int best = 0;
	    int bestpos = -1;

	    for (d = fmax; d >= fmin; d -= 2)
	      {
		int dd = d - fmid;
		if ((fd[fdiagoff + d] - xoff)*2 - dd > 12 * (c + (dd > 0 ? dd : -dd)))
		  {
		    if (fd[fdiagoff + d] * 2 - dd > best
			&& fd[fdiagoff + d] - xoff > 20
			&& fd[fdiagoff + d] - d - yoff > 20)
		      {
			int k;
			int x = fd[fdiagoff + d];

			/* We have a good enough best diagonal;
			   now insist that it end with a significant snake.  */
			for (k = 1; k <= 20; k++)
			  if (xvec[x - k] != yvec[x - d - k])
			    break;

			if (k == 21)
			  {
			    best = fd[fdiagoff + d] * 2 - dd;
			    bestpos = d;
			  }
		      }
		  }
	      }
	    if (best > 0)
	      {
		cost = 2 * c - 1;
		return bestpos;
	      }

	    best = 0;
	    for (d = bmax; d >= bmin; d -= 2)
	      {
		int dd = d - bmid;
		if ((xlim - bd[bdiagoff + d])*2 + dd > 12 * (c + (dd > 0 ? dd : -dd)))
		  {
		    if ((xlim - bd[bdiagoff + d]) * 2 + dd > best
			&& xlim - bd[bdiagoff + d] > 20
			&& ylim - (bd[bdiagoff + d] - d) > 20)
		      {
			/* We have a good enough best diagonal;
			   now insist that it end with a significant snake.  */
			int k;
			int x = bd[bdiagoff + d];

			for (k = 0; k < 20; k++)
			  if (xvec[x + k] != yvec[x - d + k])
			    break;
			if (k == 20)
			  {
			    best = (xlim - bd[bdiagoff + d]) * 2 + dd;
			    bestpos = d;
			  }
		      }
		  }
	      }
	    if (best > 0)
	      {
		cost = 2 * c - 1;
		return bestpos;
	      }
	  }
      }
  }

  /** Compare in detail contiguous subsequences of the two files
     which are known, as a whole, to match each other.

     The results are recorded in the vectors filevec[N].changed_flag, by
     storing a 1 in the element for each line that is an insertion or deletion.

     The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.

     Note that XLIM, YLIM are exclusive bounds.
     All line numbers are origin-0 and discarded lines are not counted.  */

  private void compareseq (int xoff, int xlim, int yoff, int ylim) {
    /* Slide down the bottom initial diagonal. */
    while (xoff < xlim && yoff < ylim && xvec[xoff] == yvec[yoff]) {
      ++xoff; ++yoff;
    }
    /* Slide up the top initial diagonal. */
    while (xlim > xoff && ylim > yoff && xvec[xlim - 1] == yvec[ylim - 1]) {
      --xlim; --ylim;
    }
    
    /* Handle simple cases. */
    if (xoff == xlim)
      while (yoff < ylim)
	filevec[1].changed_flag[1+filevec[1].realindexes[yoff++]] = true;
    else if (yoff == ylim)
      while (xoff < xlim)
	filevec[0].changed_flag[1+filevec[0].realindexes[xoff++]] = true;
    else
      {
	/* Find a point of correspondence in the middle of the files.  */

	int d = diag (xoff, xlim, yoff, ylim);
	int c = cost;
	int f = fdiag[fdiagoff + d];
	int b = bdiag[bdiagoff + d];

	if (c == 1)
	  {
	    /* This should be impossible, because it implies that
	       one of the two subsequences is empty,
	       and that case was handled above without calling `diag'.
	       Let's verify that this is true.  */
	    throw new IllegalArgumentException("Empty subsequence");
	  }
	else
	  {
	    /* Use that point to split this problem into two subproblems.  */
	    compareseq (xoff, b, yoff, b - d);
	    /* This used to use f instead of b,
	       but that is incorrect!
	       It is not necessarily the case that diagonal d
	       has a snake from b to f.  */
	    compareseq (b, xlim, b - d, ylim);
	  }
      }
  }

  /** Discard lines from one file that have no matches in the other file.
   */

  private void discard_confusing_lines() {
    filevec[0].discard_confusing_lines(filevec[1]);
    filevec[1].discard_confusing_lines(filevec[0]);
  }

  private boolean inhibit = false;

  /** Adjust inserts/deletes of blank lines to join changes
     as much as possible.
   */

  private void shift_boundaries() {
    if (inhibit)
      return;
    filevec[0].shift_boundaries(filevec[1]);
    filevec[1].shift_boundaries(filevec[0]);
  }

  public interface ScriptBuilder {
  /** Scan the tables of which lines are inserted and deleted,
     producing an edit script. 
   @param changed0 true for lines in first file which do not match 2nd
   @param len0 number of lines in first file
   @param changed1 true for lines in 2nd file which do not match 1st
   @param len1 number of lines in 2nd file
   @return a linked list of changes - or null
   */
    public change build_script(
      boolean[] changed0,int len0,
      boolean[] changed1,int len1
    );
  }

  /** Scan the tables of which lines are inserted and deleted,
     producing an edit script in reverse order.  */

  static class ReverseScript implements ScriptBuilder {
    public  change build_script(
	final boolean[] changed0,int len0,
	final boolean[] changed1,int len1)
    {
      change script = null;
      int i0 = 0, i1 = 0;
      while (i0 < len0 || i1 < len1) {
	if (changed0[1+i0] || changed1[1+i1]) {
	    int line0 = i0, line1 = i1;

	    /* Find # lines changed here in each file.  */
	    while (changed0[1+i0]) ++i0;
	    while (changed1[1+i1]) ++i1;

	    /* Record this change.  */
	    script = new change(line0, line1, i0 - line0, i1 - line1, script);
	}

	/* We have reached lines in the two files that match each other.  */
	i0++; i1++;
      }

      return script;
    }
  }

  static class ForwardScript implements ScriptBuilder {
    /** Scan the tables of which lines are inserted and deleted,
       producing an edit script in forward order.  */
    public change build_script(
	  final boolean[] changed0,int len0,
	  final boolean[] changed1,int len1)
    {
      change script = null;
      int i0 = len0, i1 = len1;

      while (i0 >= 0 || i1 >= 0)
	{
	  if (changed0[i0] || changed1[i1])
	    {
	      int line0 = i0, line1 = i1;

	      /* Find # lines changed here in each file.  */
	      while (changed0[i0]) --i0;
	      while (changed1[i1]) --i1;

	      /* Record this change.  */
	      script = new change(i0, i1, line0 - i0, line1 - i1, script);
	    }

	  /* We have reached lines in the two files that match each other.  */
	  i0--; i1--;
	}

      return script;
    }
  }

  /** Standard ScriptBuilders. */
  public final static ScriptBuilder
    forwardScript = new ForwardScript(),
    reverseScript = new ReverseScript();

  /* Report the differences of two files.  DEPTH is the current directory
     depth. */
  public final change diff_2(final boolean reverse) {