2 * Copyright (C) 2005 Junio C Hamano
8 #include "count-delta.h"
10 static int should_break(struct diff_filespec
*src
,
11 struct diff_filespec
*dst
,
15 /* dst is recorded as a modification of src. Are they so
16 * different that we are better off recording this as a pair
17 * of delete and create?
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
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
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.
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
47 * The value we return is 1 if we want the pair to be broken,
51 unsigned long delta_size
, base_size
, src_copied
, literal_added
;
54 *merge_score_p
= 0; /* assume no deletion --- "do not break"
58 if (!S_ISREG(src
->mode
) || !S_ISREG(dst
->mode
))
59 return 0; /* leave symlink rename alone */
61 if (diff_populate_filespec(src
, 0) || diff_populate_filespec(dst
, 0))
62 return 0; /* error but caught downstream */
64 delta_size
= ((src
->size
< dst
->size
) ?
65 (dst
->size
- src
->size
) : (src
->size
- dst
->size
));
67 /* Notice that we use max of src and dst as the base size,
68 * unlike rename similarity detection. This is so that we do
69 * not mistake a large addition as a complete rewrite.
71 base_size
= ((src
->size
< dst
->size
) ? dst
->size
: src
->size
);
73 delta
= diff_delta(src
->data
, src
->size
,
77 /* Estimate the edit size by interpreting delta. */
78 if (count_delta(delta
, delta_size
,
79 &src_copied
, &literal_added
)) {
81 return 0; /* we cannot tell */
85 /* Compute merge-score, which is "how much is removed
86 * from the source material". The clean-up stage will
87 * merge the surviving pair together if the score is
88 * less than the minimum, after rename/copy runs.
90 if (src
->size
<= src_copied
)
91 delta_size
= 0; /* avoid wrapping around */
93 delta_size
= src
->size
- src_copied
;
94 *merge_score_p
= delta_size
* MAX_SCORE
/ src
->size
;
96 /* Extent of damage, which counts both inserts and
99 if (src
->size
+ literal_added
<= src_copied
)
100 delta_size
= 0; /* avoid wrapping around */
102 delta_size
= (src
->size
- src_copied
) + literal_added
;
104 /* We break if the edit exceeds the minimum.
105 * i.e. (break_score / MAX_SCORE < delta_size / base_size)
107 if (break_score
* base_size
< delta_size
* MAX_SCORE
)
113 void diffcore_break(int break_score
)
115 struct diff_queue_struct
*q
= &diff_queued_diff
;
116 struct diff_queue_struct outq
;
118 /* When the filepair has this much edit (insert and delete),
119 * it is first considered to be a rewrite and broken into a
120 * create and delete filepair. This is to help breaking a
121 * file that had too much new stuff added, possibly from
122 * moving contents from another file, so that rename/copy can
123 * match it with the other file.
125 * int break_score; we reuse incoming parameter for this.
128 /* After a pair is broken according to break_score and
129 * subjected to rename/copy, both of them may survive intact,
130 * due to lack of suitable rename/copy peer. Or, the caller
131 * may be calling us without using rename/copy. When that
132 * happens, we merge the broken pieces back into one
133 * modification together if the pair did not have more than
134 * this much delete. For this computation, we do not take
135 * insert into account at all. If you start from a 100-line
136 * file and delete 97 lines of it, it does not matter if you
137 * add 27 lines to it to make a new 30-line file or if you add
138 * 997 lines to it to make a 1000-line file. Either way what
139 * you did was a rewrite of 97%. On the other hand, if you
140 * delete 3 lines, keeping 97 lines intact, it does not matter
141 * if you add 3 lines to it to make a new 100-line file or if
142 * you add 903 lines to it to make a new 1000-line file.
143 * Either way you did a lot of additions and not a rewrite.
144 * This merge happens to catch the latter case. A merge_score
145 * of 80% would be a good default value (a broken pair that
146 * has score lower than merge_score will be merged back
152 /* See comment on DEFAULT_BREAK_SCORE and
153 * DEFAULT_MERGE_SCORE in diffcore.h
155 merge_score
= (break_score
>> 16) & 0xFFFF;
156 break_score
= (break_score
& 0xFFFF);
159 break_score
= DEFAULT_BREAK_SCORE
;
161 merge_score
= DEFAULT_MERGE_SCORE
;
163 outq
.nr
= outq
.alloc
= 0;
166 for (i
= 0; i
< q
->nr
; i
++) {
167 struct diff_filepair
*p
= q
->queue
[i
];
170 /* We deal only with in-place edit of non directory.
171 * We do not break anything else.
173 if (DIFF_FILE_VALID(p
->one
) && DIFF_FILE_VALID(p
->two
) &&
174 !S_ISDIR(p
->one
->mode
) && !S_ISDIR(p
->two
->mode
) &&
175 !strcmp(p
->one
->path
, p
->two
->path
)) {
176 if (should_break(p
->one
, p
->two
,
177 break_score
, &score
)) {
178 /* Split this into delete and create */
179 struct diff_filespec
*null_one
, *null_two
;
180 struct diff_filepair
*dp
;
182 /* Set score to 0 for the pair that
183 * needs to be merged back together
184 * should they survive rename/copy.
185 * Also we do not want to break very
188 if ((score
< merge_score
) ||
189 (p
->one
->size
< MINIMUM_BREAK_SIZE
))
192 /* deletion of one */
193 null_one
= alloc_filespec(p
->one
->path
);
194 dp
= diff_queue(&outq
, p
->one
, null_one
);
198 /* creation of two */
199 null_two
= alloc_filespec(p
->two
->path
);
200 dp
= diff_queue(&outq
, null_two
, p
->two
);
204 free(p
); /* not diff_free_filepair(), we are
205 * reusing one and two here.
218 static void merge_broken(struct diff_filepair
*p
,
219 struct diff_filepair
*pp
,
220 struct diff_queue_struct
*outq
)
222 /* p and pp are broken pairs we want to merge */
223 struct diff_filepair
*c
= p
, *d
= pp
;
224 if (DIFF_FILE_VALID(p
->one
)) {
225 /* this must be a delete half */
229 if (!DIFF_FILE_VALID(d
->one
))
230 die("internal error in merge #1");
231 if (DIFF_FILE_VALID(d
->two
))
232 die("internal error in merge #2");
233 if (DIFF_FILE_VALID(c
->one
))
234 die("internal error in merge #3");
235 if (!DIFF_FILE_VALID(c
->two
))
236 die("internal error in merge #4");
238 diff_queue(outq
, d
->one
, c
->two
);
239 diff_free_filespec_data(d
->two
);
240 diff_free_filespec_data(c
->one
);
245 void diffcore_merge_broken(void)
247 struct diff_queue_struct
*q
= &diff_queued_diff
;
248 struct diff_queue_struct outq
;
251 outq
.nr
= outq
.alloc
= 0;
254 for (i
= 0; i
< q
->nr
; i
++) {
255 struct diff_filepair
*p
= q
->queue
[i
];
257 /* we already merged this with its peer */
259 else if (p
->broken_pair
&&
261 !strcmp(p
->one
->path
, p
->two
->path
)) {
262 /* If the peer also survived rename/copy, then
263 * we merge them back together.
265 for (j
= i
+ 1; j
< q
->nr
; j
++) {
266 struct diff_filepair
*pp
= q
->queue
[j
];
267 if (pp
->broken_pair
&&
269 !strcmp(pp
->one
->path
, pp
->two
->path
) &&
270 !strcmp(p
->one
->path
, pp
->two
->path
)) {
271 /* Peer survived. Merge them */
272 merge_broken(p
, pp
, &outq
);
278 /* The peer did not survive, so we keep