2 * Copyright (C) 2005 Junio C Hamano
8 static int should_break(struct diff_filespec
*src
,
9 struct diff_filespec
*dst
,
13 /* dst is recorded as a modification of src. Are they so
14 * different that we are better off recording this as a pair
15 * of delete and create?
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
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
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.
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
45 * The value we return is 1 if we want the pair to be broken,
48 unsigned long delta_size
, max_size
;
49 unsigned long src_copied
, literal_added
, src_removed
;
51 *merge_score_p
= 0; /* assume no deletion --- "do not break"
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 */
60 if (src
->sha1_valid
&& dst
->sha1_valid
&&
61 !hashcmp(src
->sha1
, dst
->sha1
))
62 return 0; /* they are the same */
64 if (diff_populate_filespec(src
, 0) || diff_populate_filespec(dst
, 0))
65 return 0; /* error but caught downstream */
67 max_size
= ((src
->size
> dst
->size
) ? src
->size
: dst
->size
);
68 if (max_size
< MINIMUM_BREAK_SIZE
)
69 return 0; /* we do not break too small filepair */
71 if (diffcore_count_changes(src
, dst
,
74 &src_copied
, &literal_added
))
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
;
86 src_removed
= src
->size
- src_copied
;
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.
93 *merge_score_p
= (int)(src_removed
* MAX_SCORE
/ src
->size
);
94 if (*merge_score_p
> break_score
)
97 /* Extent of damage, which counts both inserts and
100 delta_size
= src_removed
+ literal_added
;
101 if (delta_size
* MAX_SCORE
/ max_size
< break_score
)
104 /* If you removed a lot without adding new material, that is
105 * not really a rewrite.
107 if ((src
->size
* break_score
< src_removed
* MAX_SCORE
) &&
108 (literal_added
* 20 < src_removed
) &&
109 (literal_added
* 20 < src_copied
))
115 void diffcore_break(int break_score
)
117 struct diff_queue_struct
*q
= &diff_queued_diff
;
118 struct diff_queue_struct outq
;
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.
127 * int break_score; we reuse incoming parameter for this.
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
154 /* See comment on DEFAULT_BREAK_SCORE and
155 * DEFAULT_MERGE_SCORE in diffcore.h
157 merge_score
= (break_score
>> 16) & 0xFFFF;
158 break_score
= (break_score
& 0xFFFF);
161 break_score
= DEFAULT_BREAK_SCORE
;
163 merge_score
= DEFAULT_MERGE_SCORE
;
165 outq
.nr
= outq
.alloc
= 0;
168 for (i
= 0; i
< q
->nr
; i
++) {
169 struct diff_filepair
*p
= q
->queue
[i
];
173 * We deal only with in-place edit of blobs.
174 * We do not break anything else.
176 if (DIFF_FILE_VALID(p
->one
) && DIFF_FILE_VALID(p
->two
) &&
177 object_type(p
->one
->mode
) == OBJ_BLOB
&&
178 object_type(p
->two
->mode
) == OBJ_BLOB
&&
179 !strcmp(p
->one
->path
, p
->two
->path
)) {
180 if (should_break(p
->one
, p
->two
,
181 break_score
, &score
)) {
182 /* Split this into delete and create */
183 struct diff_filespec
*null_one
, *null_two
;
184 struct diff_filepair
*dp
;
186 /* Set score to 0 for the pair that
187 * needs to be merged back together
188 * should they survive rename/copy.
189 * Also we do not want to break very
192 if (score
< merge_score
)
195 /* deletion of one */
196 null_one
= alloc_filespec(p
->one
->path
);
197 dp
= diff_queue(&outq
, p
->one
, null_one
);
201 /* creation of two */
202 null_two
= alloc_filespec(p
->two
->path
);
203 dp
= diff_queue(&outq
, null_two
, p
->two
);
207 free(p
); /* not diff_free_filepair(), we are
208 * reusing one and two here.
221 static void merge_broken(struct diff_filepair
*p
,
222 struct diff_filepair
*pp
,
223 struct diff_queue_struct
*outq
)
225 /* p and pp are broken pairs we want to merge */
226 struct diff_filepair
*c
= p
, *d
= pp
, *dp
;
227 if (DIFF_FILE_VALID(p
->one
)) {
228 /* this must be a delete half */
232 if (!DIFF_FILE_VALID(d
->one
))
233 die("internal error in merge #1");
234 if (DIFF_FILE_VALID(d
->two
))
235 die("internal error in merge #2");
236 if (DIFF_FILE_VALID(c
->one
))
237 die("internal error in merge #3");
238 if (!DIFF_FILE_VALID(c
->two
))
239 die("internal error in merge #4");
241 dp
= diff_queue(outq
, d
->one
, c
->two
);
242 dp
->score
= p
->score
;
243 diff_free_filespec_data(d
->two
);
244 diff_free_filespec_data(c
->one
);
249 void diffcore_merge_broken(void)
251 struct diff_queue_struct
*q
= &diff_queued_diff
;
252 struct diff_queue_struct outq
;
255 outq
.nr
= outq
.alloc
= 0;
258 for (i
= 0; i
< q
->nr
; i
++) {
259 struct diff_filepair
*p
= q
->queue
[i
];
261 /* we already merged this with its peer */
263 else if (p
->broken_pair
&&
264 !strcmp(p
->one
->path
, p
->two
->path
)) {
265 /* If the peer also survived rename/copy, then
266 * we merge them back together.
268 for (j
= i
+ 1; j
< q
->nr
; j
++) {
269 struct diff_filepair
*pp
= q
->queue
[j
];
270 if (pp
->broken_pair
&&
271 !strcmp(pp
->one
->path
, pp
->two
->path
) &&
272 !strcmp(p
->one
->path
, pp
->two
->path
)) {
273 /* Peer survived. Merge them */
274 merge_broken(p
, pp
, &outq
);
280 /* The peer did not survive, so we keep