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Diffstat (limited to 'diffcore-break.c')
| -rw-r--r-- | diffcore-break.c | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/diffcore-break.c b/diffcore-break.c new file mode 100644 index 0000000..31cdcfe --- /dev/null +++ b/diffcore-break.c @@ -0,0 +1,293 @@ +/* + * Copyright (C) 2005 Junio C Hamano + */ +#include "cache.h" +#include "diff.h" +#include "diffcore.h" + +static int should_break(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, base_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->sha1_valid && dst->sha1_valid && + !hashcmp(src->sha1, dst->sha1)) + return 0; /* they are the same */ + + if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0)) + return 0; /* error but caught downstream */ + + base_size = ((src->size < dst->size) ? src->size : dst->size); + 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 (diffcore_count_changes(src, dst, + NULL, NULL, + 0, + &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(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; + + outq.nr = outq.alloc = 0; + outq.queue = NULL; + + 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(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; + + free(p); /* not diff_free_filepair(), we are + * reusing one and two here. + */ + continue; + } + } + 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; + 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; + + outq.nr = outq.alloc = 0; + outq.queue = NULL; + + 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; +} |