diffcore-rename: split out the delta counting code.
[git/git.git] / diffcore-break.c
CommitLineData
f345b0a0
JH
1/*
2 * Copyright (C) 2005 Junio C Hamano
3 */
4#include "cache.h"
5#include "diff.h"
6#include "diffcore.h"
f345b0a0 7
eeaa4603
JH
8static int should_break(struct diff_filespec *src,
9 struct diff_filespec *dst,
10 int break_score,
11 int *merge_score_p)
f345b0a0
JH
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 *
eeaa4603
JH
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 */
355e76a4 48 unsigned long delta_size, base_size, src_copied, literal_added;
eeaa4603
JH
49 int to_break = 0;
50
51 *merge_score_p = 0; /* assume no deletion --- "do not break"
52 * is the default.
53 */
f345b0a0
JH
54
55 if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
56 return 0; /* leave symlink rename alone */
57
aeecd23a
JH
58 if (src->sha1_valid && dst->sha1_valid &&
59 !memcmp(src->sha1, dst->sha1, 20))
60 return 0; /* they are the same */
61
eeaa4603 62 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
f345b0a0
JH
63 return 0; /* error but caught downstream */
64
f78c79c5 65 base_size = ((src->size < dst->size) ? src->size : dst->size);
0532a5e4
JH
66 if (base_size < MINIMUM_BREAK_SIZE)
67 return 0; /* we do not break too small filepair */
f345b0a0 68
65416758
JH
69 if (diffcore_count_changes(src->data, src->size,
70 dst->data, dst->size,
71 0,
72 &src_copied, &literal_added))
73 return 0;
355e76a4 74
eeaa4603
JH
75 /* Compute merge-score, which is "how much is removed
76 * from the source material". The clean-up stage will
77 * merge the surviving pair together if the score is
78 * less than the minimum, after rename/copy runs.
79 */
80 if (src->size <= src_copied)
f78c79c5
JH
81 ; /* all copied, nothing removed */
82 else {
eeaa4603 83 delta_size = src->size - src_copied;
f78c79c5
JH
84 *merge_score_p = delta_size * MAX_SCORE / src->size;
85 }
eeaa4603
JH
86
87 /* Extent of damage, which counts both inserts and
88 * deletes.
89 */
90 if (src->size + literal_added <= src_copied)
91 delta_size = 0; /* avoid wrapping around */
355e76a4
JH
92 else
93 delta_size = (src->size - src_copied) + literal_added;
eeaa4603
JH
94
95 /* We break if the edit exceeds the minimum.
96 * i.e. (break_score / MAX_SCORE < delta_size / base_size)
97 */
98 if (break_score * base_size < delta_size * MAX_SCORE)
99 to_break = 1;
f345b0a0 100
eeaa4603 101 return to_break;
f345b0a0
JH
102}
103
eeaa4603 104void diffcore_break(int break_score)
f345b0a0
JH
105{
106 struct diff_queue_struct *q = &diff_queued_diff;
107 struct diff_queue_struct outq;
eeaa4603
JH
108
109 /* When the filepair has this much edit (insert and delete),
110 * it is first considered to be a rewrite and broken into a
111 * create and delete filepair. This is to help breaking a
112 * file that had too much new stuff added, possibly from
113 * moving contents from another file, so that rename/copy can
114 * match it with the other file.
115 *
116 * int break_score; we reuse incoming parameter for this.
117 */
118
119 /* After a pair is broken according to break_score and
120 * subjected to rename/copy, both of them may survive intact,
121 * due to lack of suitable rename/copy peer. Or, the caller
122 * may be calling us without using rename/copy. When that
123 * happens, we merge the broken pieces back into one
124 * modification together if the pair did not have more than
125 * this much delete. For this computation, we do not take
126 * insert into account at all. If you start from a 100-line
127 * file and delete 97 lines of it, it does not matter if you
128 * add 27 lines to it to make a new 30-line file or if you add
129 * 997 lines to it to make a 1000-line file. Either way what
130 * you did was a rewrite of 97%. On the other hand, if you
131 * delete 3 lines, keeping 97 lines intact, it does not matter
132 * if you add 3 lines to it to make a new 100-line file or if
133 * you add 903 lines to it to make a new 1000-line file.
134 * Either way you did a lot of additions and not a rewrite.
135 * This merge happens to catch the latter case. A merge_score
136 * of 80% would be a good default value (a broken pair that
137 * has score lower than merge_score will be merged back
138 * together).
139 */
140 int merge_score;
f345b0a0
JH
141 int i;
142
eeaa4603
JH
143 /* See comment on DEFAULT_BREAK_SCORE and
144 * DEFAULT_MERGE_SCORE in diffcore.h
145 */
146 merge_score = (break_score >> 16) & 0xFFFF;
147 break_score = (break_score & 0xFFFF);
148
149 if (!break_score)
150 break_score = DEFAULT_BREAK_SCORE;
151 if (!merge_score)
152 merge_score = DEFAULT_MERGE_SCORE;
f345b0a0
JH
153
154 outq.nr = outq.alloc = 0;
155 outq.queue = NULL;
156
157 for (i = 0; i < q->nr; i++) {
158 struct diff_filepair *p = q->queue[i];
159 int score;
160
161 /* We deal only with in-place edit of non directory.
162 * We do not break anything else.
163 */
164 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
165 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) &&
166 !strcmp(p->one->path, p->two->path)) {
eeaa4603 167 if (should_break(p->one, p->two,
0532a5e4 168 break_score, &score)) {
f345b0a0
JH
169 /* Split this into delete and create */
170 struct diff_filespec *null_one, *null_two;
171 struct diff_filepair *dp;
172
eeaa4603
JH
173 /* Set score to 0 for the pair that
174 * needs to be merged back together
175 * should they survive rename/copy.
176 * Also we do not want to break very
177 * small files.
178 */
f78c79c5 179 if (score < merge_score)
eeaa4603
JH
180 score = 0;
181
f345b0a0
JH
182 /* deletion of one */
183 null_one = alloc_filespec(p->one->path);
184 dp = diff_queue(&outq, p->one, null_one);
185 dp->score = score;
186 dp->broken_pair = 1;
187
188 /* creation of two */
189 null_two = alloc_filespec(p->two->path);
190 dp = diff_queue(&outq, null_two, p->two);
191 dp->score = score;
192 dp->broken_pair = 1;
193
194 free(p); /* not diff_free_filepair(), we are
195 * reusing one and two here.
196 */
197 continue;
198 }
199 }
200 diff_q(&outq, p);
201 }
202 free(q->queue);
203 *q = outq;
204
205 return;
206}
eeaa4603
JH
207
208static void merge_broken(struct diff_filepair *p,
209 struct diff_filepair *pp,
210 struct diff_queue_struct *outq)
211{
212 /* p and pp are broken pairs we want to merge */
366175ef 213 struct diff_filepair *c = p, *d = pp, *dp;
eeaa4603
JH
214 if (DIFF_FILE_VALID(p->one)) {
215 /* this must be a delete half */
216 d = p; c = pp;
217 }
218 /* Sanity check */
219 if (!DIFF_FILE_VALID(d->one))
220 die("internal error in merge #1");
221 if (DIFF_FILE_VALID(d->two))
222 die("internal error in merge #2");
223 if (DIFF_FILE_VALID(c->one))
224 die("internal error in merge #3");
225 if (!DIFF_FILE_VALID(c->two))
226 die("internal error in merge #4");
227
366175ef
JH
228 dp = diff_queue(outq, d->one, c->two);
229 dp->score = p->score;
19397b45
JH
230 diff_free_filespec_data(d->two);
231 diff_free_filespec_data(c->one);
eeaa4603
JH
232 free(d);
233 free(c);
234}
235
236void diffcore_merge_broken(void)
237{
238 struct diff_queue_struct *q = &diff_queued_diff;
239 struct diff_queue_struct outq;
240 int i, j;
241
242 outq.nr = outq.alloc = 0;
243 outq.queue = NULL;
244
245 for (i = 0; i < q->nr; i++) {
246 struct diff_filepair *p = q->queue[i];
247 if (!p)
248 /* we already merged this with its peer */
249 continue;
250 else if (p->broken_pair &&
eeaa4603
JH
251 !strcmp(p->one->path, p->two->path)) {
252 /* If the peer also survived rename/copy, then
253 * we merge them back together.
254 */
255 for (j = i + 1; j < q->nr; j++) {
256 struct diff_filepair *pp = q->queue[j];
257 if (pp->broken_pair &&
eeaa4603
JH
258 !strcmp(pp->one->path, pp->two->path) &&
259 !strcmp(p->one->path, pp->two->path)) {
260 /* Peer survived. Merge them */
261 merge_broken(p, pp, &outq);
262 q->queue[j] = NULL;
263 break;
264 }
265 }
266 if (q->nr <= j)
267 /* The peer did not survive, so we keep
268 * it in the output.
269 */
270 diff_q(&outq, p);
271 }
272 else
273 diff_q(&outq, p);
274 }
275 free(q->queue);
276 *q = outq;
277
278 return;
279}