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f345b0a [PATCH] Add -B flag to diff-* brothers.
Junio C Hamano authored
1 /*
2 * Copyright (C) 2005 Junio C Hamano
3 */
4 #include "cache.h"
5 #include "diff.h"
6 #include "diffcore.h"
7 #include "delta.h"
8 #include "count-delta.h"
9
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10 static int should_break(struct diff_filespec *src,
11 struct diff_filespec *dst,
12 int break_score,
13 int *merge_score_p)
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14 {
15 /* dst is recorded as a modification of src. Are they so
16 * different that we are better off recording this as a pair
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17 * of delete and create?
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18 *
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19 * There are two criteria used in this algorithm. For the
20 * purposes of helping later rename/copy, we take both delete
21 * and insert into account and estimate the amount of "edit".
22 * If the edit is very large, we break this pair so that
23 * rename/copy can pick the pieces up to match with other
24 * files.
25 *
26 * On the other hand, we would want to ignore inserts for the
27 * pure "complete rewrite" detection. As long as most of the
28 * existing contents were removed from the file, it is a
29 * complete rewrite, and if sizable chunk from the original
30 * still remains in the result, it is not a rewrite. It does
31 * not matter how much or how little new material is added to
32 * the file.
33 *
34 * The score we leave for such a broken filepair uses the
35 * latter definition so that later clean-up stage can find the
36 * pieces that should not have been broken according to the
37 * latter definition after rename/copy runs, and merge the
38 * broken pair that have a score lower than given criteria
39 * back together. The break operation itself happens
40 * according to the former definition.
41 *
42 * The minimum_edit parameter tells us when to break (the
43 * amount of "edit" required for us to consider breaking the
44 * pair). We leave the amount of deletion in *merge_score_p
45 * when we return.
46 *
47 * The value we return is 1 if we want the pair to be broken,
48 * or 0 if we do not.
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49 */
50 void *delta;
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51 unsigned long delta_size, base_size, src_copied, literal_added;
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52 int to_break = 0;
53
54 *merge_score_p = 0; /* assume no deletion --- "do not break"
55 * is the default.
56 */
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57
58 if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
59 return 0; /* leave symlink rename alone */
60
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61 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
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62 return 0; /* error but caught downstream */
63
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64 base_size = ((src->size < dst->size) ? src->size : dst->size);
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65
66 delta = diff_delta(src->data, src->size,
67 dst->data, dst->size,
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68 &delta_size, 0);
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69
70 /* Estimate the edit size by interpreting delta. */
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71 if (count_delta(delta, delta_size,
72 &src_copied, &literal_added)) {
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73 free(delta);
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74 return 0; /* we cannot tell */
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75 }
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76 free(delta);
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77
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78 /* Compute merge-score, which is "how much is removed
79 * from the source material". The clean-up stage will
80 * merge the surviving pair together if the score is
81 * less than the minimum, after rename/copy runs.
82 */
83 if (src->size <= src_copied)
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84 ; /* all copied, nothing removed */
85 else {
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86 delta_size = src->size - src_copied;
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87 *merge_score_p = delta_size * MAX_SCORE / src->size;
88 }
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89
90 /* Extent of damage, which counts both inserts and
91 * deletes.
92 */
93 if (src->size + literal_added <= src_copied)
94 delta_size = 0; /* avoid wrapping around */
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95 else
96 delta_size = (src->size - src_copied) + literal_added;
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97
98 /* We break if the edit exceeds the minimum.
99 * i.e. (break_score / MAX_SCORE < delta_size / base_size)
100 */
101 if (break_score * base_size < delta_size * MAX_SCORE)
102 to_break = 1;
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103
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104 return to_break;
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105 }
106
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107 void diffcore_break(int break_score)
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108 {
109 struct diff_queue_struct *q = &diff_queued_diff;
110 struct diff_queue_struct outq;
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111
112 /* When the filepair has this much edit (insert and delete),
113 * it is first considered to be a rewrite and broken into a
114 * create and delete filepair. This is to help breaking a
115 * file that had too much new stuff added, possibly from
116 * moving contents from another file, so that rename/copy can
117 * match it with the other file.
118 *
119 * int break_score; we reuse incoming parameter for this.
120 */
121
122 /* After a pair is broken according to break_score and
123 * subjected to rename/copy, both of them may survive intact,
124 * due to lack of suitable rename/copy peer. Or, the caller
125 * may be calling us without using rename/copy. When that
126 * happens, we merge the broken pieces back into one
127 * modification together if the pair did not have more than
128 * this much delete. For this computation, we do not take
129 * insert into account at all. If you start from a 100-line
130 * file and delete 97 lines of it, it does not matter if you
131 * add 27 lines to it to make a new 30-line file or if you add
132 * 997 lines to it to make a 1000-line file. Either way what
133 * you did was a rewrite of 97%. On the other hand, if you
134 * delete 3 lines, keeping 97 lines intact, it does not matter
135 * if you add 3 lines to it to make a new 100-line file or if
136 * you add 903 lines to it to make a new 1000-line file.
137 * Either way you did a lot of additions and not a rewrite.
138 * This merge happens to catch the latter case. A merge_score
139 * of 80% would be a good default value (a broken pair that
140 * has score lower than merge_score will be merged back
141 * together).
142 */
143 int merge_score;
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144 int i;
145
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146 /* See comment on DEFAULT_BREAK_SCORE and
147 * DEFAULT_MERGE_SCORE in diffcore.h
148 */
149 merge_score = (break_score >> 16) & 0xFFFF;
150 break_score = (break_score & 0xFFFF);
151
152 if (!break_score)
153 break_score = DEFAULT_BREAK_SCORE;
154 if (!merge_score)
155 merge_score = DEFAULT_MERGE_SCORE;
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156
157 outq.nr = outq.alloc = 0;
158 outq.queue = NULL;
159
160 for (i = 0; i < q->nr; i++) {
161 struct diff_filepair *p = q->queue[i];
162 int score;
163
164 /* We deal only with in-place edit of non directory.
165 * We do not break anything else.
166 */
167 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
168 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) &&
169 !strcmp(p->one->path, p->two->path)) {
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170 if (should_break(p->one, p->two,
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171 break_score, &score) &&
172 MINIMUM_BREAK_SIZE <= p->one->size) {
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173 /* Split this into delete and create */
174 struct diff_filespec *null_one, *null_two;
175 struct diff_filepair *dp;
176
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177 /* Set score to 0 for the pair that
178 * needs to be merged back together
179 * should they survive rename/copy.
180 * Also we do not want to break very
181 * small files.
182 */
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183 if (score < merge_score)
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184 score = 0;
185
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186 /* deletion of one */
187 null_one = alloc_filespec(p->one->path);
188 dp = diff_queue(&outq, p->one, null_one);
189 dp->score = score;
190 dp->broken_pair = 1;
191
192 /* creation of two */
193 null_two = alloc_filespec(p->two->path);
194 dp = diff_queue(&outq, null_two, p->two);
195 dp->score = score;
196 dp->broken_pair = 1;
197
198 free(p); /* not diff_free_filepair(), we are
199 * reusing one and two here.
200 */
201 continue;
202 }
203 }
204 diff_q(&outq, p);
205 }
206 free(q->queue);
207 *q = outq;
208
209 return;
210 }
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211
212 static void merge_broken(struct diff_filepair *p,
213 struct diff_filepair *pp,
214 struct diff_queue_struct *outq)
215 {
216 /* p and pp are broken pairs we want to merge */
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217 struct diff_filepair *c = p, *d = pp, *dp;
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218 if (DIFF_FILE_VALID(p->one)) {
219 /* this must be a delete half */
220 d = p; c = pp;
221 }
222 /* Sanity check */
223 if (!DIFF_FILE_VALID(d->one))
224 die("internal error in merge #1");
225 if (DIFF_FILE_VALID(d->two))
226 die("internal error in merge #2");
227 if (DIFF_FILE_VALID(c->one))
228 die("internal error in merge #3");
229 if (!DIFF_FILE_VALID(c->two))
230 die("internal error in merge #4");
231
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232 dp = diff_queue(outq, d->one, c->two);
233 dp->score = p->score;
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234 diff_free_filespec_data(d->two);
235 diff_free_filespec_data(c->one);
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236 free(d);
237 free(c);
238 }
239
240 void diffcore_merge_broken(void)
241 {
242 struct diff_queue_struct *q = &diff_queued_diff;
243 struct diff_queue_struct outq;
244 int i, j;
245
246 outq.nr = outq.alloc = 0;
247 outq.queue = NULL;
248
249 for (i = 0; i < q->nr; i++) {
250 struct diff_filepair *p = q->queue[i];
251 if (!p)
252 /* we already merged this with its peer */
253 continue;
254 else if (p->broken_pair &&
255 !strcmp(p->one->path, p->two->path)) {
256 /* If the peer also survived rename/copy, then
257 * we merge them back together.
258 */
259 for (j = i + 1; j < q->nr; j++) {
260 struct diff_filepair *pp = q->queue[j];
261 if (pp->broken_pair &&
262 !strcmp(pp->one->path, pp->two->path) &&
263 !strcmp(p->one->path, pp->two->path)) {
264 /* Peer survived. Merge them */
265 merge_broken(p, pp, &outq);
266 q->queue[j] = NULL;
267 break;
268 }
269 }
270 if (q->nr <= j)
271 /* The peer did not survive, so we keep
272 * it in the output.
273 */
274 diff_q(&outq, p);
275 }
276 else
277 diff_q(&outq, p);
278 }
279 free(q->queue);
280 *q = outq;
281
282 return;
283 }
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