Formed in 2009, the Archive Team (not to be confused with the archive.org Archive-It Team) is a rogue archivist collective dedicated to saving copies of rapidly dying or deleted websites for the sake of history and digital heritage. The group is 100% composed of volunteers and interested parties, and has expanded into a large amount of related projects for saving online and digital history.
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| /* | |
| * Copyright (C) 2005 Junio C Hamano | |
| */ | |
| #include "cache.h" | |
| #include "diff.h" | |
| #include "diffcore.h" | |
| #include "promisor-remote.h" | |
| static int should_break(struct repository *r, | |
| struct diff_filespec *src, | |
| struct diff_filespec *dst, | |
| int break_score, | |
| int *merge_score_p) | |
| { | |
| /* dst is recorded as a modification of src. Are they so | |
| * different that we are better off recording this as a pair | |
| * of delete and create? | |
| * | |
| * There are two criteria used in this algorithm. For the | |
| * purposes of helping later rename/copy, we take both delete | |
| * and insert into account and estimate the amount of "edit". | |
| * If the edit is very large, we break this pair so that | |
| * rename/copy can pick the pieces up to match with other | |
| * files. | |
| * | |
| * On the other hand, we would want to ignore inserts for the | |
| * pure "complete rewrite" detection. As long as most of the | |
| * existing contents were removed from the file, it is a | |
| * complete rewrite, and if sizable chunk from the original | |
| * still remains in the result, it is not a rewrite. It does | |
| * not matter how much or how little new material is added to | |
| * the file. | |
| * | |
| * The score we leave for such a broken filepair uses the | |
| * latter definition so that later clean-up stage can find the | |
| * pieces that should not have been broken according to the | |
| * latter definition after rename/copy runs, and merge the | |
| * broken pair that have a score lower than given criteria | |
| * back together. The break operation itself happens | |
| * according to the former definition. | |
| * | |
| * The minimum_edit parameter tells us when to break (the | |
| * amount of "edit" required for us to consider breaking the | |
| * pair). We leave the amount of deletion in *merge_score_p | |
| * when we return. | |
| * | |
| * The value we return is 1 if we want the pair to be broken, | |
| * or 0 if we do not. | |
| */ | |
| unsigned long delta_size, max_size; | |
| unsigned long src_copied, literal_added, src_removed; | |
| struct diff_populate_filespec_options options = { 0 }; | |
| *merge_score_p = 0; /* assume no deletion --- "do not break" | |
| * is the default. | |
| */ | |
| if (S_ISREG(src->mode) != S_ISREG(dst->mode)) { | |
| *merge_score_p = (int)MAX_SCORE; | |
| return 1; /* even their types are different */ | |
| } | |
| if (src->oid_valid && dst->oid_valid && | |
| oideq(&src->oid, &dst->oid)) | |
| return 0; /* they are the same */ | |
| if (r == the_repository && has_promisor_remote()) { | |
| options.missing_object_cb = diff_queued_diff_prefetch; | |
| options.missing_object_data = r; | |
| } | |
| if (diff_populate_filespec(r, src, &options) || | |
| diff_populate_filespec(r, dst, &options)) | |
| return 0; /* error but caught downstream */ | |
| max_size = ((src->size > dst->size) ? src->size : dst->size); | |
| if (max_size < MINIMUM_BREAK_SIZE) | |
| return 0; /* we do not break too small filepair */ | |
| if (!src->size) | |
| return 0; /* we do not let empty files get renamed */ | |
| if (diffcore_count_changes(r, src, dst, | |
| &src->cnt_data, &dst->cnt_data, | |
| &src_copied, &literal_added)) | |
| return 0; | |
| /* sanity */ | |
| if (src->size < src_copied) | |
| src_copied = src->size; | |
| if (dst->size < literal_added + src_copied) { | |
| if (src_copied < dst->size) | |
| literal_added = dst->size - src_copied; | |
| else | |
| literal_added = 0; | |
| } | |
| src_removed = src->size - src_copied; | |
| /* Compute merge-score, which is "how much is removed | |
| * from the source material". The clean-up stage will | |
| * merge the surviving pair together if the score is | |
| * less than the minimum, after rename/copy runs. | |
| */ | |
| *merge_score_p = (int)(src_removed * MAX_SCORE / src->size); | |
| if (*merge_score_p > break_score) | |
| return 1; | |
| /* Extent of damage, which counts both inserts and | |
| * deletes. | |
| */ | |
| delta_size = src_removed + literal_added; | |
| if (delta_size * MAX_SCORE / max_size < break_score) | |
| return 0; | |
| /* If you removed a lot without adding new material, that is | |
| * not really a rewrite. | |
| */ | |
| if ((src->size * break_score < src_removed * MAX_SCORE) && | |
| (literal_added * 20 < src_removed) && | |
| (literal_added * 20 < src_copied)) | |
| return 0; | |
| return 1; | |
| } | |
| void diffcore_break(struct repository *r, int break_score) | |
| { | |
| struct diff_queue_struct *q = &diff_queued_diff; | |
| struct diff_queue_struct outq; | |
| /* When the filepair has this much edit (insert and delete), | |
| * it is first considered to be a rewrite and broken into a | |
| * create and delete filepair. This is to help breaking a | |
| * file that had too much new stuff added, possibly from | |
| * moving contents from another file, so that rename/copy can | |
| * match it with the other file. | |
| * | |
| * int break_score; we reuse incoming parameter for this. | |
| */ | |
| /* After a pair is broken according to break_score and | |
| * subjected to rename/copy, both of them may survive intact, | |
| * due to lack of suitable rename/copy peer. Or, the caller | |
| * may be calling us without using rename/copy. When that | |
| * happens, we merge the broken pieces back into one | |
| * modification together if the pair did not have more than | |
| * this much delete. For this computation, we do not take | |
| * insert into account at all. If you start from a 100-line | |
| * file and delete 97 lines of it, it does not matter if you | |
| * add 27 lines to it to make a new 30-line file or if you add | |
| * 997 lines to it to make a 1000-line file. Either way what | |
| * you did was a rewrite of 97%. On the other hand, if you | |
| * delete 3 lines, keeping 97 lines intact, it does not matter | |
| * if you add 3 lines to it to make a new 100-line file or if | |
| * you add 903 lines to it to make a new 1000-line file. | |
| * Either way you did a lot of additions and not a rewrite. | |
| * This merge happens to catch the latter case. A merge_score | |
| * of 80% would be a good default value (a broken pair that | |
| * has score lower than merge_score will be merged back | |
| * together). | |
| */ | |
| int merge_score; | |
| int i; | |
| /* See comment on DEFAULT_BREAK_SCORE and | |
| * DEFAULT_MERGE_SCORE in diffcore.h | |
| */ | |
| merge_score = (break_score >> 16) & 0xFFFF; | |
| break_score = (break_score & 0xFFFF); | |
| if (!break_score) | |
| break_score = DEFAULT_BREAK_SCORE; | |
| if (!merge_score) | |
| merge_score = DEFAULT_MERGE_SCORE; | |
| DIFF_QUEUE_CLEAR(&outq); | |
| for (i = 0; i < q->nr; i++) { | |
| struct diff_filepair *p = q->queue[i]; | |
| int score; | |
| /* | |
| * We deal only with in-place edit of blobs. | |
| * We do not break anything else. | |
| */ | |
| if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && | |
| object_type(p->one->mode) == OBJ_BLOB && | |
| object_type(p->two->mode) == OBJ_BLOB && | |
| !strcmp(p->one->path, p->two->path)) { | |
| if (should_break(r, p->one, p->two, | |
| break_score, &score)) { | |
| /* Split this into delete and create */ | |
| struct diff_filespec *null_one, *null_two; | |
| struct diff_filepair *dp; | |
| /* Set score to 0 for the pair that | |
| * needs to be merged back together | |
| * should they survive rename/copy. | |
| * Also we do not want to break very | |
| * small files. | |
| */ | |
| if (score < merge_score) | |
| score = 0; | |
| /* deletion of one */ | |
| null_one = alloc_filespec(p->one->path); | |
| dp = diff_queue(&outq, p->one, null_one); | |
| dp->score = score; | |
| dp->broken_pair = 1; | |
| /* creation of two */ | |
| null_two = alloc_filespec(p->two->path); | |
| dp = diff_queue(&outq, null_two, p->two); | |
| dp->score = score; | |
| dp->broken_pair = 1; | |
| diff_free_filespec_blob(p->one); | |
| diff_free_filespec_blob(p->two); | |
| free(p); /* not diff_free_filepair(), we are | |
| * reusing one and two here. | |
| */ | |
| continue; | |
| } | |
| } | |
| diff_free_filespec_data(p->one); | |
| diff_free_filespec_data(p->two); | |
| diff_q(&outq, p); | |
| } | |
| free(q->queue); | |
| *q = outq; | |
| return; | |
| } | |
| static void merge_broken(struct diff_filepair *p, | |
| struct diff_filepair *pp, | |
| struct diff_queue_struct *outq) | |
| { | |
| /* p and pp are broken pairs we want to merge */ | |
| struct diff_filepair *c = p, *d = pp, *dp; | |
| if (DIFF_FILE_VALID(p->one)) { | |
| /* this must be a delete half */ | |
| d = p; c = pp; | |
| } | |
| /* Sanity check */ | |
| if (!DIFF_FILE_VALID(d->one)) | |
| die("internal error in merge #1"); | |
| if (DIFF_FILE_VALID(d->two)) | |
| die("internal error in merge #2"); | |
| if (DIFF_FILE_VALID(c->one)) | |
| die("internal error in merge #3"); | |
| if (!DIFF_FILE_VALID(c->two)) | |
| die("internal error in merge #4"); | |
| dp = diff_queue(outq, d->one, c->two); | |
| dp->score = p->score; | |
| /* | |
| * We will be one extra user of the same src side of the | |
| * broken pair, if it was used as the rename source for other | |
| * paths elsewhere. Increment to mark that the path stays | |
| * in the resulting tree. | |
| */ | |
| d->one->rename_used++; | |
| diff_free_filespec_data(d->two); | |
| diff_free_filespec_data(c->one); | |
| free(d); | |
| free(c); | |
| } | |
| void diffcore_merge_broken(void) | |
| { | |
| struct diff_queue_struct *q = &diff_queued_diff; | |
| struct diff_queue_struct outq; | |
| int i, j; | |
| DIFF_QUEUE_CLEAR(&outq); | |
| for (i = 0; i < q->nr; i++) { | |
| struct diff_filepair *p = q->queue[i]; | |
| if (!p) | |
| /* we already merged this with its peer */ | |
| continue; | |
| else if (p->broken_pair && | |
| !strcmp(p->one->path, p->two->path)) { | |
| /* If the peer also survived rename/copy, then | |
| * we merge them back together. | |
| */ | |
| for (j = i + 1; j < q->nr; j++) { | |
| struct diff_filepair *pp = q->queue[j]; | |
| if (pp->broken_pair && | |
| !strcmp(pp->one->path, pp->two->path) && | |
| !strcmp(p->one->path, pp->two->path)) { | |
| /* Peer survived. Merge them */ | |
| merge_broken(p, pp, &outq); | |
| q->queue[j] = NULL; | |
| goto next; | |
| } | |
| } | |
| /* The peer did not survive, so we keep | |
| * it in the output. | |
| */ | |
| diff_q(&outq, p); | |
| } | |
| else | |
| diff_q(&outq, p); | |
| next:; | |
| } | |
| free(q->queue); | |
| *q = outq; | |
| return; | |
| } |