source: josm/trunk/src/org/openstreetmap/josm/tools/Diff.java@ 10375

Last change on this file since 10375 was 10308, checked in by Don-vip, 8 years ago

sonar - squid:S1854 - Dead stores should be removed
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1// License: GPL. For details, see LICENSE file.
2package org.openstreetmap.josm.tools;
3
4//// Taken from http://www.bmsi.com/java/#diff
5
6// http://www.bmsi.com/java/DiffPrint.java could also be useful
7
8/*
9 * $Log: Diff.java,v $
10 * Revision 1.15 2013/04/01 16:27:31 stuart
11 * Fix DiffPrint unified format with test cases.
12 * Begin porting some diff-2.7 features.
13 *
14 * Revision 1.14 2010/03/03 21:21:25 stuart
15 * Test new direct equivalence API
16 *
17 * Revision 1.13 2009/12/07 17:43:17 stuart
18 * Compute equivMax for int[] ctor
19 *
20 * Revision 1.12 2009/12/07 17:34:46 stuart
21 * Ctor with int[].
22 *
23 * Revision 1.11 2009/11/15 01:11:54 stuart
24 * Diff doesn't need to be generic
25 *
26 * Revision 1.10 2009/11/15 00:54:03 stuart
27 * Update to Java 5 containers
28 *
29 * Revision 1.7 2009/01/19 03:05:26 stuart
30 * Fix StackOverflow bug with heuristic on reported by Jimmy Han.
31 *
32 * Revision 1.6 2003/03/06 22:51:32 stuart
33 * Convert to CVS
34 *
35 * Revision 1.5 2002/07/19 19:14:40 stuart
36 * fix reverseScript, make change ctor public, update docs
37 *
38 * Revision 1.4 2002/04/09 17:53:39 stuart
39 * More flexible interface for diff() function.
40 *
41 * Revision 1.3 2000/03/03 21:58:03 stuart
42 * move discard_confusing_lines and shift_boundaries to class file_data
43 *
44 * Revision 1.2 2000/03/02 16:37:38 stuart
45 * Add GPL and copyright
46 *
47 */
48
49import java.util.HashMap;
50import java.util.Map;
51
52/** A class to compare vectors of objects. The result of comparison
53 is a list of <code>change</code> objects which form an
54 edit script. The objects compared are traditionally lines
55 of text from two files. Comparison options such as "ignore
56 whitespace" are implemented by modifying the <code>equals</code>
57 and <code>hashcode</code> methods for the objects compared.
58<p>
59 The basic algorithm is described in: <br>
60 "An O(ND) Difference Algorithm and its Variations", Eugene Myers,
61 Algorithmica Vol. 1 No. 2, 1986, p 251.
62<p>
63 This class outputs different results from GNU diff 1.15 on some
64 inputs. Our results are actually better (smaller change list, smaller
65 total size of changes), but it would be nice to know why. Perhaps
66 there is a memory overwrite bug in GNU diff 1.15.
67
68 @author Stuart D. Gathman, translated from GNU diff 1.15
69 Copyright (C) 2000 Business Management Systems, Inc.
70<p>
71 This program is free software; you can redistribute it and/or modify
72 it under the terms of the GNU General Public License as published by
73 the Free Software Foundation; either version 1, or (at your option)
74 any later version.
75<p>
76 This program is distributed in the hope that it will be useful,
77 but WITHOUT ANY WARRANTY; without even the implied warranty of
78 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
79 GNU General Public License for more details.
80<p>
81 You should have received a copy of the <a href=COPYING.txt>
82 GNU General Public License</a>
83 along with this program; if not, write to the Free Software
84 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
85 */
86public class Diff {
87
88 /** Prepare to find differences between two arrays. Each element of
89 the arrays is translated to an "equivalence number" based on
90 the result of <code>equals</code>. The original Object arrays
91 are no longer needed for computing the differences. They will
92 be needed again later to print the results of the comparison as
93 an edit script, if desired.
94 * @param a first array
95 * @param b second array
96 */
97 public Diff(Object[] a, Object[] b) {
98 Map<Object, Integer> h = new HashMap<>(a.length + b.length);
99 filevec = new FileData[] {new FileData(a, h), new FileData(b, h)};
100 }
101
102 /** 1 more than the maximum equivalence value used for this or its
103 sibling file. */
104 private int equivMax = 1;
105
106 private int[] xvec, yvec; /* Vectors being compared. */
107 private int[] fdiag; /* Vector, indexed by diagonal, containing
108 the X coordinate of the point furthest
109 along the given diagonal in the forward
110 search of the edit matrix. */
111 private int[] bdiag; /* Vector, indexed by diagonal, containing
112 the X coordinate of the point furthest
113 along the given diagonal in the backward
114 search of the edit matrix. */
115 private int fdiagoff, bdiagoff;
116 private final FileData[] filevec;
117 private int cost;
118
119 /**
120 * Find the midpoint of the shortest edit script for a specified
121 * portion of the two files.
122 *
123 * We scan from the beginnings of the files, and simultaneously from the ends,
124 * doing a breadth-first search through the space of edit-sequence.
125 * When the two searches meet, we have found the midpoint of the shortest
126 * edit sequence.
127 *
128 * The value returned is the number of the diagonal on which the midpoint lies.
129 * The diagonal number equals the number of inserted lines minus the number
130 * of deleted lines (counting only lines before the midpoint).
131 * The edit cost is stored into COST; this is the total number of
132 * lines inserted or deleted (counting only lines before the midpoint).
133 *
134 * This function assumes that the first lines of the specified portions
135 * of the two files do not match, and likewise that the last lines do not
136 * match. The caller must trim matching lines from the beginning and end
137 * of the portions it is going to specify.
138 *
139 * Note that if we return the "wrong" diagonal value, or if
140 * the value of bdiag at that diagonal is "wrong",
141 * the worst this can do is cause suboptimal diff output.
142 * It cannot cause incorrect diff output.
143 * @param xoff xoff
144 * @param xlim xlim
145 * @param yoff yoff
146 * @param ylim ylim
147 * @return midpoint of the shortest edit script
148 */
149 private int diag(int xoff, int xlim, int yoff, int ylim) {
150 final int[] fd = fdiag; // Give the compiler a chance.
151 final int[] bd = bdiag; // Additional help for the compiler.
152 final int[] xv = xvec; // Still more help for the compiler.
153 final int[] yv = yvec; // And more and more . . .
154 final int dmin = xoff - ylim; // Minimum valid diagonal.
155 final int dmax = xlim - yoff; // Maximum valid diagonal.
156 final int fmid = xoff - yoff; // Center diagonal of top-down search.
157 final int bmid = xlim - ylim; // Center diagonal of bottom-up search.
158 int fmin = fmid, fmax = fmid; // Limits of top-down search.
159 int bmin = bmid, bmax = bmid; // Limits of bottom-up search.
160 // True if southeast corner is on an odd diagonal with respect to the northwest.
161 final boolean odd = (fmid - bmid & 1) != 0;
162
163 fd[fdiagoff + fmid] = xoff;
164 bd[bdiagoff + bmid] = xlim;
165
166 for (int c = 1;; ++c) {
167 int d; /* Active diagonal. */
168
169 /* Extend the top-down search by an edit step in each diagonal. */
170 if (fmin > dmin) {
171 fd[fdiagoff + --fmin - 1] = -1;
172 } else {
173 ++fmin;
174 }
175 if (fmax < dmax) {
176 fd[fdiagoff + ++fmax + 1] = -1;
177 } else {
178 --fmax;
179 }
180 for (d = fmax; d >= fmin; d -= 2) {
181 int x, y, tlo = fd[fdiagoff + d - 1], thi = fd[fdiagoff + d + 1];
182
183 if (tlo >= thi) {
184 x = tlo + 1;
185 } else {
186 x = thi;
187 }
188 y = x - d;
189 while (x < xlim && y < ylim && xv[x] == yv[y]) {
190 ++x; ++y;
191 }
192 fd[fdiagoff + d] = x;
193 if (odd && bmin <= d && d <= bmax && bd[bdiagoff + d] <= fd[fdiagoff + d]) {
194 cost = 2 * c - 1;
195 return d;
196 }
197 }
198
199 /* Similar extend the bottom-up search. */
200 if (bmin > dmin) {
201 bd[bdiagoff + --bmin - 1] = Integer.MAX_VALUE;
202 } else {
203 ++bmin;
204 }
205 if (bmax < dmax) {
206 bd[bdiagoff + ++bmax + 1] = Integer.MAX_VALUE;
207 } else {
208 --bmax;
209 }
210 for (d = bmax; d >= bmin; d -= 2) {
211 int x, y, tlo = bd[bdiagoff + d - 1], thi = bd[bdiagoff + d + 1];
212
213 if (tlo < thi) {
214 x = tlo;
215 } else {
216 x = thi - 1;
217 }
218 y = x - d;
219 while (x > xoff && y > yoff && xv[x - 1] == yv[y - 1]) {
220 --x; --y;
221 }
222 bd[bdiagoff + d] = x;
223 if (!odd && fmin <= d && d <= fmax && bd[bdiagoff + d] <= fd[fdiagoff + d]) {
224 cost = 2 * c;
225 return d;
226 }
227 }
228 }
229 }
230
231 /**
232 * Compare in detail contiguous subsequences of the two files
233 * which are known, as a whole, to match each other.
234 *
235 * The results are recorded in the vectors filevec[N].changed_flag, by
236 * storing a 1 in the element for each line that is an insertion or deletion.
237 *
238 * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
239 *
240 * Note that XLIM, YLIM are exclusive bounds.
241 * All line numbers are origin-0 and discarded lines are not counted.
242 * @param xoff xoff
243 * @param xlim xlim
244 * @param yoff yoff
245 * @param ylim ylim
246 */
247 private void compareseq(int xoff, int xlim, int yoff, int ylim) {
248 /* Slide down the bottom initial diagonal. */
249 while (xoff < xlim && yoff < ylim && xvec[xoff] == yvec[yoff]) {
250 ++xoff; ++yoff;
251 }
252 /* Slide up the top initial diagonal. */
253 while (xlim > xoff && ylim > yoff && xvec[xlim - 1] == yvec[ylim - 1]) {
254 --xlim; --ylim;
255 }
256
257 /* Handle simple cases. */
258 if (xoff == xlim) {
259 while (yoff < ylim) {
260 filevec[1].changedFlag[1+filevec[1].realindexes[yoff++]] = true;
261 }
262 } else if (yoff == ylim) {
263 while (xoff < xlim) {
264 filevec[0].changedFlag[1+filevec[0].realindexes[xoff++]] = true;
265 }
266 } else {
267 /* Find a point of correspondence in the middle of the files. */
268
269 int d = diag(xoff, xlim, yoff, ylim);
270 int c = cost;
271 int b = bdiag[bdiagoff + d];
272
273 if (c == 1)
274 /* This should be impossible, because it implies that
275 one of the two subsequences is empty,
276 and that case was handled above without calling `diag'.
277 Let's verify that this is true. */
278 throw new IllegalArgumentException("Empty subsequence");
279 else {
280 /* Use that point to split this problem into two subproblems. */
281 compareseq(xoff, b, yoff, b - d);
282 /* This used to use f instead of b,
283 but that is incorrect!
284 It is not necessarily the case that diagonal d
285 has a snake from b to f. */
286 compareseq(b, xlim, b - d, ylim);
287 }
288 }
289 }
290
291 /** Discard lines from one file that have no matches in the other file.
292 */
293 private void discard_confusing_lines() {
294 filevec[0].discard_confusing_lines(filevec[1]);
295 filevec[1].discard_confusing_lines(filevec[0]);
296 }
297
298 /**
299 * Adjust inserts/deletes of blank lines to join changes as much as possible.
300 */
301 private void shift_boundaries() {
302 filevec[0].shift_boundaries(filevec[1]);
303 filevec[1].shift_boundaries(filevec[0]);
304 }
305
306 /**
307 * Script builder.
308 */
309 public interface ScriptBuilder {
310 /**
311 * Scan the tables of which lines are inserted and deleted, producing an edit script.
312 * @param changed0 true for lines in first file which do not match 2nd
313 * @param len0 number of lines in first file
314 * @param changed1 true for lines in 2nd file which do not match 1st
315 * @param len1 number of lines in 2nd file
316 * @return a linked list of changes - or null
317 */
318 Change build_script(
319 boolean[] changed0, int len0,
320 boolean[] changed1, int len1
321 );
322 }
323
324 /** Scan the tables of which lines are inserted and deleted,
325 producing an edit script in reverse order. */
326
327 static class ReverseScript implements ScriptBuilder {
328 @Override
329 public Change build_script(
330 final boolean[] changed0, int len0,
331 final boolean[] changed1, int len1) {
332 Change script = null;
333 int i0 = 0, i1 = 0;
334 while (i0 < len0 || i1 < len1) {
335 if (changed0[1+i0] || changed1[1+i1]) {
336 int line0 = i0, line1 = i1;
337
338 /* Find # lines changed here in each file. */
339 while (changed0[1+i0]) {
340 ++i0;
341 }
342 while (changed1[1+i1]) {
343 ++i1;
344 }
345
346 /* Record this change. */
347 script = new Change(line0, line1, i0 - line0, i1 - line1, script);
348 }
349
350 /* We have reached lines in the two files that match each other. */
351 i0++; i1++;
352 }
353
354 return script;
355 }
356 }
357
358 static class ForwardScript implements ScriptBuilder {
359 /** Scan the tables of which lines are inserted and deleted,
360 producing an edit script in forward order. */
361 @Override
362 public Change build_script(
363 final boolean[] changed0, int len0,
364 final boolean[] changed1, int len1) {
365 Change script = null;
366 int i0 = len0, i1 = len1;
367
368 while (i0 >= 0 || i1 >= 0) {
369 if (changed0[i0] || changed1[i1]) {
370 int line0 = i0, line1 = i1;
371
372 /* Find # lines changed here in each file. */
373 while (changed0[i0]) {
374 --i0;
375 }
376 while (changed1[i1]) {
377 --i1;
378 }
379
380 /* Record this change. */
381 script = new Change(i0, i1, line0 - i0, line1 - i1, script);
382 }
383
384 /* We have reached lines in the two files that match each other. */
385 i0--; i1--;
386 }
387
388 return script;
389 }
390 }
391
392 /** Standard Forward ScriptBuilder. */
393 public static final ScriptBuilder forwardScript = new ForwardScript();
394 /** Standard Reverse ScriptBuilder. */
395 public static final ScriptBuilder reverseScript = new ReverseScript();
396
397 /**
398 * Report the differences of two files. DEPTH is the current directory depth.
399 * @param reverse if {@code true} use {@link #reverseScript} else use {@link #forwardScript}
400 * @return the differences of two files
401 */
402 public final Change diff_2(final boolean reverse) {
403 return diff(reverse ? reverseScript : forwardScript);
404 }
405
406 /**
407 * Get the results of comparison as an edit script. The script
408 * is described by a list of changes. The standard ScriptBuilder
409 * implementations provide for forward and reverse edit scripts.
410 * Alternate implementations could, for instance, list common elements
411 * instead of differences.
412 * @param bld an object to build the script from change flags
413 * @return the head of a list of changes
414 */
415 public Change diff(final ScriptBuilder bld) {
416
417 // Some lines are obviously insertions or deletions because they don't match anything.
418 // Detect them now, and avoid even thinking about them in the main comparison algorithm.
419 discard_confusing_lines();
420
421 // Now do the main comparison algorithm, considering just the undiscarded lines.
422 xvec = filevec[0].undiscarded;
423 yvec = filevec[1].undiscarded;
424
425 int diags = filevec[0].nondiscardedLines + filevec[1].nondiscardedLines + 3;
426 fdiag = new int[diags];
427 fdiagoff = filevec[1].nondiscardedLines + 1;
428 bdiag = new int[diags];
429 bdiagoff = filevec[1].nondiscardedLines + 1;
430
431 compareseq(0, filevec[0].nondiscardedLines,
432 0, filevec[1].nondiscardedLines);
433 fdiag = null;
434 bdiag = null;
435
436 // Modify the results slightly to make them prettier in cases where that can validly be done.
437 shift_boundaries();
438
439 // Get the results of comparison in the form of a chain of `struct change's -- an edit script.
440 return bld.build_script(
441 filevec[0].changedFlag,
442 filevec[0].bufferedLines,
443 filevec[1].changedFlag,
444 filevec[1].bufferedLines
445 );
446 }
447
448 /** The result of comparison is an "edit script": a chain of change objects.
449 Each change represents one place where some lines are deleted
450 and some are inserted.
451
452 LINE0 and LINE1 are the first affected lines in the two files (origin 0).
453 DELETED is the number of lines deleted here from file 0.
454 INSERTED is the number of lines inserted here in file 1.
455
456 If DELETED is 0 then LINE0 is the number of the line before
457 which the insertion was done; vice versa for INSERTED and LINE1. */
458
459 public static class Change {
460 /** Previous or next edit command. */
461 public Change link;
462 /** # lines of file 1 changed here. */
463 public final int inserted;
464 /** # lines of file 0 changed here. */
465 public final int deleted;
466 /** Line number of 1st deleted line. */
467 public final int line0;
468 /** Line number of 1st inserted line. */
469 public final int line1;
470
471 /**
472 * Cons an additional entry onto the front of an edit script OLD.
473 * LINE0 and LINE1 are the first affected lines in the two files (origin 0).
474 * DELETED is the number of lines deleted here from file 0.
475 * INSERTED is the number of lines inserted here in file 1.
476 *
477 * If DELETED is 0 then LINE0 is the number of the line before
478 * which the insertion was done; vice versa for INSERTED and LINE1.
479 * @param line0 first affected lines in the two files (origin 0)
480 * @param line1 first affected lines in the two files (origin 0)
481 * @param deleted the number of lines deleted here from file 0
482 * @param inserted the number of lines inserted here in file 1
483 * @param old edit script
484 */
485 public Change(int line0, int line1, int deleted, int inserted, Change old) {
486 this.line0 = line0;
487 this.line1 = line1;
488 this.inserted = inserted;
489 this.deleted = deleted;
490 this.link = old;
491 }
492
493 /**
494 * Returns the number of insertions and deletions of this change as well as
495 * (recursively) the changes linked via {@link #link}.
496 * @return recursive number of insertions and deletions
497 */
498 public int getTotalNumberOfChanges() {
499 return inserted + deleted + (link != null ? link.getTotalNumberOfChanges() : 0);
500 }
501
502 @Override
503 public String toString() {
504 String s = String.format("%d -%d +%d %d", line0, deleted, inserted, line1);
505 return (link != null) ? s + '\n' + link : s;
506 }
507 }
508
509 /**
510 * Data on one input file being compared.
511 */
512 class FileData {
513
514 /** Allocate changed array for the results of comparison. */
515 void clear() {
516 // Allocate a flag for each line of each file, saying whether that line is an insertion or deletion.
517 // Allocate an extra element, always zero, at each end of each vector.
518 changedFlag = new boolean[bufferedLines + 2];
519 }
520
521 /**
522 * Return equiv_count[I] as the number of lines in this file that fall in equivalence class I.
523 * @return the array of equivalence class counts.
524 */
525 int[] equivCount() {
526 int[] equivCount = new int[equivMax];
527 for (int i = 0; i < bufferedLines; ++i) {
528 ++equivCount[equivs[i]];
529 }
530 return equivCount;
531 }
532
533 /**
534 * Discard lines that have no matches in another file.
535 *
536 * A line which is discarded will not be considered by the actual comparison algorithm;
537 * it will be as if that line were not in the file.
538 * The file's `realindexes' table maps virtual line numbers
539 * (which don't count the discarded lines) into real line numbers;
540 * this is how the actual comparison algorithm produces results
541 * that are comprehensible when the discarded lines are counted.
542 * <p>
543 * When we discard a line, we also mark it as a deletion or insertion so that it will be printed in the output.
544 * @param f the other file
545 */
546 void discard_confusing_lines(FileData f) {
547 clear();
548 // Set up table of which lines are going to be discarded.
549 final byte[] discarded = discardable(f.equivCount());
550
551 // Don't really discard the provisional lines except when they occur in a run of discardables,
552 // with nonprovisionals at the beginning and end.
553 filterDiscards(discarded);
554
555 // Actually discard the lines.
556 discard(discarded);
557 }
558
559 /**
560 * Mark to be discarded each line that matches no line of another file.
561 * If a line matches many lines, mark it as provisionally discardable.
562 * @param counts The count of each equivalence number for the other file.
563 * @return 0=nondiscardable, 1=discardable or 2=provisionally discardable for each line
564 * @see #equivCount()
565 */
566 private byte[] discardable(final int[] counts) {
567 final int end = bufferedLines;
568 final byte[] discards = new byte[end];
569 final int[] equivs = this.equivs;
570 int many = 5;
571 int tem = end / 64;
572
573 /* Multiply MANY by approximate square root of number of lines.
574 That is the threshold for provisionally discardable lines. */
575 while ((tem = tem >> 2) > 0) {
576 many *= 2;
577 }
578
579 for (int i = 0; i < end; i++) {
580 int nmatch;
581 if (equivs[i] == 0) {
582 continue;
583 }
584 nmatch = counts[equivs[i]];
585 if (nmatch == 0) {
586 discards[i] = 1;
587 } else if (nmatch > many) {
588 discards[i] = 2;
589 }
590 }
591 return discards;
592 }
593
594 /**
595 * Don't really discard the provisional lines except when they occur
596 * in a run of discardables, with nonprovisionals at the beginning and end.
597 * @param discards discards
598 */
599 private void filterDiscards(final byte[] discards) {
600 final int end = bufferedLines;
601
602 for (int i = 0; i < end; i++) {
603 /* Cancel provisional discards not in middle of run of discards. */
604 if (discards[i] == 2) {
605 discards[i] = 0;
606 } else if (discards[i] != 0) {
607 /* We have found a nonprovisional discard. */
608 int j;
609 int length;
610 int provisional = 0;
611
612 /* Find end of this run of discardable lines.
613 Count how many are provisionally discardable. */
614 for (j = i; j < end; j++) {
615 if (discards[j] == 0) {
616 break;
617 }
618 if (discards[j] == 2) {
619 ++provisional;
620 }
621 }
622
623 /* Cancel provisional discards at end, and shrink the run. */
624 while (j > i && discards[j - 1] == 2) {
625 discards[--j] = 0; --provisional;
626 }
627
628 /* Now we have the length of a run of discardable lines
629 whose first and last are not provisional. */
630 length = j - i;
631
632 /* If 1/4 of the lines in the run are provisional,
633 cancel discarding of all provisional lines in the run. */
634 if (provisional * 4 > length) {
635 while (j > i)
636 if (discards[--j] == 2) {
637 discards[j] = 0;
638 }
639 } else {
640 int consec;
641 int minimum = 1;
642 int tem = length / 4;
643
644 /* MINIMUM is approximate square root of LENGTH/4.
645 A subrun of two or more provisionals can stand
646 when LENGTH is at least 16.
647 A subrun of 4 or more can stand when LENGTH >= 64. */
648 while ((tem = tem >> 2) > 0) {
649 minimum *= 2;
650 }
651 minimum++;
652
653 /* Cancel any subrun of MINIMUM or more provisionals
654 within the larger run. */
655 for (j = 0, consec = 0; j < length; j++) {
656 if (discards[i + j] != 2) {
657 consec = 0;
658 } else if (minimum == ++consec) {
659 /* Back up to start of subrun, to cancel it all. */
660 j -= consec;
661 } else if (minimum < consec) {
662 discards[i + j] = 0;
663 }
664 }
665
666 /* Scan from beginning of run
667 until we find 3 or more nonprovisionals in a row
668 or until the first nonprovisional at least 8 lines in.
669 Until that point, cancel any provisionals. */
670 for (j = 0, consec = 0; j < length; j++) {
671 if (j >= 8 && discards[i + j] == 1) {
672 break;
673 }
674 if (discards[i + j] == 2) {
675 consec = 0; discards[i + j] = 0;
676 } else if (discards[i + j] == 0) {
677 consec = 0;
678 } else {
679 consec++;
680 }
681 if (consec == 3) {
682 break;
683 }
684 }
685
686 /* I advances to the last line of the run. */
687 i += length - 1;
688
689 /* Same thing, from end. */
690 for (j = 0, consec = 0; j < length; j++) {
691 if (j >= 8 && discards[i - j] == 1) {
692 break;
693 }
694 if (discards[i - j] == 2) {
695 consec = 0; discards[i - j] = 0;
696 } else if (discards[i - j] == 0) {
697 consec = 0;
698 } else {
699 consec++;
700 }
701 if (consec == 3) {
702 break;
703 }
704 }
705 }
706 }
707 }
708 }
709
710 /** Actually discard the lines.
711 @param discards flags lines to be discarded
712 */
713 private void discard(final byte[] discards) {
714 final int end = bufferedLines;
715 int j = 0;
716 for (int i = 0; i < end; ++i) {
717 if (discards[i] == 0) {
718 undiscarded[j] = equivs[i];
719 realindexes[j++] = i;
720 } else {
721 changedFlag[1+i] = true;
722 }
723 }
724 nondiscardedLines = j;
725 }
726
727 FileData(int length) {
728 bufferedLines = length;
729 equivs = new int[length];
730 undiscarded = new int[bufferedLines];
731 realindexes = new int[bufferedLines];
732 }
733
734 FileData(Object[] data, Map<Object, Integer> h) {
735 this(data.length);
736 // FIXME: diff 2.7 removes common prefix and common suffix
737 for (int i = 0; i < data.length; ++i) {
738 Integer ir = h.get(data[i]);
739 if (ir == null) {
740 equivs[i] = equivMax++;
741 h.put(data[i], equivs[i]);
742 } else {
743 equivs[i] = ir.intValue();
744 }
745 }
746 }
747
748 /** Adjust inserts/deletes of blank lines to join changes
749 as much as possible.
750
751 We do something when a run of changed lines include a blank
752 line at one end and have an excluded blank line at the other.
753 We are free to choose which blank line is included.
754 `compareseq' always chooses the one at the beginning,
755 but usually it is cleaner to consider the following blank line
756 to be the "change". The only exception is if the preceding blank line
757 would join this change to other changes.
758 @param f the file being compared against
759 */
760 void shift_boundaries(FileData f) {
761 final boolean[] changed = changedFlag;
762 final boolean[] otherChanged = f.changedFlag;
763 int i = 0;
764 int j = 0;
765 int iEnd = bufferedLines;
766 int preceding = -1;
767 int otherPreceding = -1;
768
769 for (;;) {
770 int start, end, otherStart;
771
772 /* Scan forwards to find beginning of another run of changes.
773 Also keep track of the corresponding point in the other file. */
774
775 while (i < iEnd && !changed[1+i]) {
776 while (otherChanged[1+j++]) {
777 /* Non-corresponding lines in the other file
778 will count as the preceding batch of changes. */
779 otherPreceding = j;
780 }
781 i++;
782 }
783
784 if (i == iEnd) {
785 break;
786 }
787
788 start = i;
789 otherStart = j;
790
791 for (;;) {
792 /* Now find the end of this run of changes. */
793
794 while (i < iEnd && changed[1+i]) {
795 i++;
796 }
797 end = i;
798
799 /* If the first changed line matches the following unchanged one,
800 and this run does not follow right after a previous run,
801 and there are no lines deleted from the other file here,
802 then classify the first changed line as unchanged
803 and the following line as changed in its place. */
804
805 /* You might ask, how could this run follow right after another?
806 Only because the previous run was shifted here. */
807
808 if (end != iEnd && equivs[start] == equivs[end] && !otherChanged[1+j]
809 && !((preceding >= 0 && start == preceding) || (otherPreceding >= 0 && otherStart == otherPreceding))) {
810 changed[1+end++] = true;
811 changed[1+start++] = false;
812 ++i;
813 /* Since one line-that-matches is now before this run
814 instead of after, we must advance in the other file
815 to keep in synch. */
816 ++j;
817 } else {
818 break;
819 }
820 }
821
822 preceding = i;
823 otherPreceding = j;
824 }
825 }
826
827 /** Number of elements (lines) in this file. */
828 private final int bufferedLines;
829
830 /** Vector, indexed by line number, containing an equivalence code for
831 each line. It is this vector that is actually compared with that
832 of another file to generate differences. */
833 private final int[] equivs;
834
835 /** Vector, like the previous one except that
836 the elements for discarded lines have been squeezed out. */
837 private final int[] undiscarded;
838
839 /** Vector mapping virtual line numbers (not counting discarded lines)
840 to real ones (counting those lines). Both are origin-0. */
841 private final int[] realindexes;
842
843 /** Total number of nondiscarded lines. */
844 private int nondiscardedLines;
845
846 /** Array, indexed by real origin-1 line number,
847 containing true for a line that is an insertion or a deletion.
848 The results of comparison are stored here. */
849 private boolean[] changedFlag;
850 }
851}
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