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[git/git.git] / diffcore-break.c
CommitLineData
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1/*
2 * Copyright (C) 2005 Junio C Hamano
3 */
4#include "cache.h"
5#include "diff.h"
6#include "diffcore.h"
f345b0a0 7
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8static int should_break(struct diff_filespec *src,
9 struct diff_filespec *dst,
10 int break_score,
11 int *merge_score_p)
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12{
13 /* dst is recorded as a modification of src. Are they so
14 * different that we are better off recording this as a pair
eeaa4603 15 * of delete and create?
f345b0a0 16 *
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17 * There are two criteria used in this algorithm. For the
18 * purposes of helping later rename/copy, we take both delete
19 * and insert into account and estimate the amount of "edit".
20 * If the edit is very large, we break this pair so that
21 * rename/copy can pick the pieces up to match with other
22 * files.
23 *
24 * On the other hand, we would want to ignore inserts for the
25 * pure "complete rewrite" detection. As long as most of the
26 * existing contents were removed from the file, it is a
27 * complete rewrite, and if sizable chunk from the original
28 * still remains in the result, it is not a rewrite. It does
29 * not matter how much or how little new material is added to
30 * the file.
31 *
32 * The score we leave for such a broken filepair uses the
33 * latter definition so that later clean-up stage can find the
34 * pieces that should not have been broken according to the
35 * latter definition after rename/copy runs, and merge the
36 * broken pair that have a score lower than given criteria
37 * back together. The break operation itself happens
38 * according to the former definition.
39 *
40 * The minimum_edit parameter tells us when to break (the
41 * amount of "edit" required for us to consider breaking the
42 * pair). We leave the amount of deletion in *merge_score_p
43 * when we return.
44 *
45 * The value we return is 1 if we want the pair to be broken,
46 * or 0 if we do not.
f345b0a0 47 */
eb3a9dd3 48 unsigned long delta_size, max_size;
6dd4b66f 49 unsigned long src_copied, literal_added, src_removed;
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50
51 *merge_score_p = 0; /* assume no deletion --- "do not break"
52 * is the default.
53 */
f345b0a0 54
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55 if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
56 *merge_score_p = (int)MAX_SCORE;
57 return 1; /* even their types are different */
58 }
f345b0a0 59
aeecd23a 60 if (src->sha1_valid && dst->sha1_valid &&
a89fccd2 61 !hashcmp(src->sha1, dst->sha1))
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62 return 0; /* they are the same */
63
eeaa4603 64 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
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65 return 0; /* error but caught downstream */
66
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67 max_size = ((src->size > dst->size) ? src->size : dst->size);
68 if (max_size < MINIMUM_BREAK_SIZE)
0532a5e4 69 return 0; /* we do not break too small filepair */
f345b0a0 70
d8c3d03a 71 if (diffcore_count_changes(src, dst,
8282de94 72 &src->cnt_data, &dst->cnt_data,
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73 0,
74 &src_copied, &literal_added))
75 return 0;
355e76a4 76
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77 /* sanity */
78 if (src->size < src_copied)
79 src_copied = src->size;
80 if (dst->size < literal_added + src_copied) {
81 if (src_copied < dst->size)
82 literal_added = dst->size - src_copied;
83 else
84 literal_added = 0;
85 }
86 src_removed = src->size - src_copied;
87
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88 /* Compute merge-score, which is "how much is removed
89 * from the source material". The clean-up stage will
90 * merge the surviving pair together if the score is
91 * less than the minimum, after rename/copy runs.
92 */
dc49cd76 93 *merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
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94 if (*merge_score_p > break_score)
95 return 1;
4d0f39ce 96
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97 /* Extent of damage, which counts both inserts and
98 * deletes.
99 */
4d0f39ce 100 delta_size = src_removed + literal_added;
6dd4b66f 101 if (delta_size * MAX_SCORE / max_size < break_score)
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102 return 0;
103
104 /* If you removed a lot without adding new material, that is
105 * not really a rewrite.
eeaa4603 106 */
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107 if ((src->size * break_score < src_removed * MAX_SCORE) &&
108 (literal_added * 20 < src_removed) &&
109 (literal_added * 20 < src_copied))
110 return 0;
f345b0a0 111
4d0f39ce 112 return 1;
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113}
114
eeaa4603 115void diffcore_break(int break_score)
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116{
117 struct diff_queue_struct *q = &diff_queued_diff;
118 struct diff_queue_struct outq;
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119
120 /* When the filepair has this much edit (insert and delete),
121 * it is first considered to be a rewrite and broken into a
122 * create and delete filepair. This is to help breaking a
123 * file that had too much new stuff added, possibly from
124 * moving contents from another file, so that rename/copy can
125 * match it with the other file.
126 *
127 * int break_score; we reuse incoming parameter for this.
128 */
129
130 /* After a pair is broken according to break_score and
131 * subjected to rename/copy, both of them may survive intact,
132 * due to lack of suitable rename/copy peer. Or, the caller
133 * may be calling us without using rename/copy. When that
134 * happens, we merge the broken pieces back into one
135 * modification together if the pair did not have more than
136 * this much delete. For this computation, we do not take
137 * insert into account at all. If you start from a 100-line
138 * file and delete 97 lines of it, it does not matter if you
139 * add 27 lines to it to make a new 30-line file or if you add
140 * 997 lines to it to make a 1000-line file. Either way what
141 * you did was a rewrite of 97%. On the other hand, if you
142 * delete 3 lines, keeping 97 lines intact, it does not matter
143 * if you add 3 lines to it to make a new 100-line file or if
144 * you add 903 lines to it to make a new 1000-line file.
145 * Either way you did a lot of additions and not a rewrite.
146 * This merge happens to catch the latter case. A merge_score
147 * of 80% would be a good default value (a broken pair that
148 * has score lower than merge_score will be merged back
149 * together).
150 */
151 int merge_score;
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152 int i;
153
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154 /* See comment on DEFAULT_BREAK_SCORE and
155 * DEFAULT_MERGE_SCORE in diffcore.h
156 */
157 merge_score = (break_score >> 16) & 0xFFFF;
158 break_score = (break_score & 0xFFFF);
159
160 if (!break_score)
161 break_score = DEFAULT_BREAK_SCORE;
162 if (!merge_score)
163 merge_score = DEFAULT_MERGE_SCORE;
f345b0a0 164
9ca5df90 165 DIFF_QUEUE_CLEAR(&outq);
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166
167 for (i = 0; i < q->nr; i++) {
168 struct diff_filepair *p = q->queue[i];
169 int score;
170
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171 /*
172 * We deal only with in-place edit of blobs.
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173 * We do not break anything else.
174 */
175 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
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176 object_type(p->one->mode) == OBJ_BLOB &&
177 object_type(p->two->mode) == OBJ_BLOB &&
f345b0a0 178 !strcmp(p->one->path, p->two->path)) {
eeaa4603 179 if (should_break(p->one, p->two,
0532a5e4 180 break_score, &score)) {
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181 /* Split this into delete and create */
182 struct diff_filespec *null_one, *null_two;
183 struct diff_filepair *dp;
184
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185 /* Set score to 0 for the pair that
186 * needs to be merged back together
187 * should they survive rename/copy.
188 * Also we do not want to break very
189 * small files.
190 */
f78c79c5 191 if (score < merge_score)
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192 score = 0;
193
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194 /* deletion of one */
195 null_one = alloc_filespec(p->one->path);
196 dp = diff_queue(&outq, p->one, null_one);
197 dp->score = score;
198 dp->broken_pair = 1;
199
200 /* creation of two */
201 null_two = alloc_filespec(p->two->path);
202 dp = diff_queue(&outq, null_two, p->two);
203 dp->score = score;
204 dp->broken_pair = 1;
205
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206 diff_free_filespec_blob(p->one);
207 diff_free_filespec_blob(p->two);
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208 free(p); /* not diff_free_filepair(), we are
209 * reusing one and two here.
210 */
211 continue;
212 }
213 }
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214 diff_free_filespec_data(p->one);
215 diff_free_filespec_data(p->two);
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216 diff_q(&outq, p);
217 }
218 free(q->queue);
219 *q = outq;
220
221 return;
222}
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223
224static void merge_broken(struct diff_filepair *p,
225 struct diff_filepair *pp,
226 struct diff_queue_struct *outq)
227{
228 /* p and pp are broken pairs we want to merge */
366175ef 229 struct diff_filepair *c = p, *d = pp, *dp;
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230 if (DIFF_FILE_VALID(p->one)) {
231 /* this must be a delete half */
232 d = p; c = pp;
233 }
234 /* Sanity check */
235 if (!DIFF_FILE_VALID(d->one))
236 die("internal error in merge #1");
237 if (DIFF_FILE_VALID(d->two))
238 die("internal error in merge #2");
239 if (DIFF_FILE_VALID(c->one))
240 die("internal error in merge #3");
241 if (!DIFF_FILE_VALID(c->two))
242 die("internal error in merge #4");
243
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244 dp = diff_queue(outq, d->one, c->two);
245 dp->score = p->score;
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246 diff_free_filespec_data(d->two);
247 diff_free_filespec_data(c->one);
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248 free(d);
249 free(c);
250}
251
252void diffcore_merge_broken(void)
253{
254 struct diff_queue_struct *q = &diff_queued_diff;
255 struct diff_queue_struct outq;
256 int i, j;
257
9ca5df90 258 DIFF_QUEUE_CLEAR(&outq);
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259
260 for (i = 0; i < q->nr; i++) {
261 struct diff_filepair *p = q->queue[i];
262 if (!p)
263 /* we already merged this with its peer */
264 continue;
265 else if (p->broken_pair &&
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266 !strcmp(p->one->path, p->two->path)) {
267 /* If the peer also survived rename/copy, then
268 * we merge them back together.
269 */
270 for (j = i + 1; j < q->nr; j++) {
271 struct diff_filepair *pp = q->queue[j];
272 if (pp->broken_pair &&
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273 !strcmp(pp->one->path, pp->two->path) &&
274 !strcmp(p->one->path, pp->two->path)) {
275 /* Peer survived. Merge them */
276 merge_broken(p, pp, &outq);
277 q->queue[j] = NULL;
278 break;
279 }
280 }
281 if (q->nr <= j)
282 /* The peer did not survive, so we keep
283 * it in the output.
284 */
285 diff_q(&outq, p);
286 }
287 else
288 diff_q(&outq, p);
289 }
290 free(q->queue);
291 *q = outq;
292
293 return;
294}