/* * Copyright (C) 2005 Junio C Hamano */ #include "cache.h" #include "diff.h" #include "diffcore.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; *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 (diff_populate_filespec(r, src, 0) || diff_populate_filespec(r, dst, 0)) 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; break; } } if (q->nr <= j) /* The peer did not survive, so we keep * it in the output. */ diff_q(&outq, p); } else diff_q(&outq, p); } free(q->queue); *q = outq; return; }