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When the source file is empty, the calculation of the merge score results in a division by zero. In the situation: == preimage == == postimage == F (empty file) F (a large file) E (a new empty file) it does not make sense to consider F->E as a rename, so it is better not to break the pre- and post-image of F. Bail out early in this case to avoid hitting the divide-by-zero. This causes the merge score to be left at zero. Signed-off-by: John Keeping <john@keeping.me.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
298 lines
8.8 KiB
C
298 lines
8.8 KiB
C
/*
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* Copyright (C) 2005 Junio C Hamano
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*/
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#include "cache.h"
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#include "diff.h"
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#include "diffcore.h"
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static int should_break(struct diff_filespec *src,
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struct diff_filespec *dst,
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int break_score,
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int *merge_score_p)
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{
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/* dst is recorded as a modification of src. Are they so
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* different that we are better off recording this as a pair
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* of delete and create?
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*
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* There are two criteria used in this algorithm. For the
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* purposes of helping later rename/copy, we take both delete
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* and insert into account and estimate the amount of "edit".
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* If the edit is very large, we break this pair so that
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* rename/copy can pick the pieces up to match with other
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* files.
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*
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* On the other hand, we would want to ignore inserts for the
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* pure "complete rewrite" detection. As long as most of the
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* existing contents were removed from the file, it is a
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* complete rewrite, and if sizable chunk from the original
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* still remains in the result, it is not a rewrite. It does
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* not matter how much or how little new material is added to
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* the file.
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*
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* The score we leave for such a broken filepair uses the
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* latter definition so that later clean-up stage can find the
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* pieces that should not have been broken according to the
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* latter definition after rename/copy runs, and merge the
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* broken pair that have a score lower than given criteria
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* back together. The break operation itself happens
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* according to the former definition.
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*
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* The minimum_edit parameter tells us when to break (the
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* amount of "edit" required for us to consider breaking the
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* pair). We leave the amount of deletion in *merge_score_p
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* when we return.
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*
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* The value we return is 1 if we want the pair to be broken,
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* or 0 if we do not.
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*/
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unsigned long delta_size, max_size;
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unsigned long src_copied, literal_added, src_removed;
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*merge_score_p = 0; /* assume no deletion --- "do not break"
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* is the default.
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*/
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if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
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*merge_score_p = (int)MAX_SCORE;
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return 1; /* even their types are different */
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}
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if (src->sha1_valid && dst->sha1_valid &&
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!hashcmp(src->sha1, dst->sha1))
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return 0; /* they are the same */
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if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
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return 0; /* error but caught downstream */
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max_size = ((src->size > dst->size) ? src->size : dst->size);
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if (max_size < MINIMUM_BREAK_SIZE)
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return 0; /* we do not break too small filepair */
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if (!src->size)
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return 0; /* we do not let empty files get renamed */
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if (diffcore_count_changes(src, dst,
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&src->cnt_data, &dst->cnt_data,
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0,
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&src_copied, &literal_added))
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return 0;
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/* sanity */
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if (src->size < src_copied)
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src_copied = src->size;
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if (dst->size < literal_added + src_copied) {
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if (src_copied < dst->size)
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literal_added = dst->size - src_copied;
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else
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literal_added = 0;
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}
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src_removed = src->size - src_copied;
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/* Compute merge-score, which is "how much is removed
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* from the source material". The clean-up stage will
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* merge the surviving pair together if the score is
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* less than the minimum, after rename/copy runs.
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*/
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*merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
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if (*merge_score_p > break_score)
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return 1;
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/* Extent of damage, which counts both inserts and
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* deletes.
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*/
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delta_size = src_removed + literal_added;
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if (delta_size * MAX_SCORE / max_size < break_score)
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return 0;
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/* If you removed a lot without adding new material, that is
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* not really a rewrite.
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*/
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if ((src->size * break_score < src_removed * MAX_SCORE) &&
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(literal_added * 20 < src_removed) &&
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(literal_added * 20 < src_copied))
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return 0;
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return 1;
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}
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void diffcore_break(int break_score)
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{
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struct diff_queue_struct *q = &diff_queued_diff;
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struct diff_queue_struct outq;
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/* When the filepair has this much edit (insert and delete),
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* it is first considered to be a rewrite and broken into a
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* create and delete filepair. This is to help breaking a
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* file that had too much new stuff added, possibly from
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* moving contents from another file, so that rename/copy can
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* match it with the other file.
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*
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* int break_score; we reuse incoming parameter for this.
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*/
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/* After a pair is broken according to break_score and
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* subjected to rename/copy, both of them may survive intact,
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* due to lack of suitable rename/copy peer. Or, the caller
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* may be calling us without using rename/copy. When that
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* happens, we merge the broken pieces back into one
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* modification together if the pair did not have more than
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* this much delete. For this computation, we do not take
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* insert into account at all. If you start from a 100-line
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* file and delete 97 lines of it, it does not matter if you
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* add 27 lines to it to make a new 30-line file or if you add
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* 997 lines to it to make a 1000-line file. Either way what
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* you did was a rewrite of 97%. On the other hand, if you
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* delete 3 lines, keeping 97 lines intact, it does not matter
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* if you add 3 lines to it to make a new 100-line file or if
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* you add 903 lines to it to make a new 1000-line file.
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* Either way you did a lot of additions and not a rewrite.
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* This merge happens to catch the latter case. A merge_score
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* of 80% would be a good default value (a broken pair that
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* has score lower than merge_score will be merged back
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* together).
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*/
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int merge_score;
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int i;
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/* See comment on DEFAULT_BREAK_SCORE and
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* DEFAULT_MERGE_SCORE in diffcore.h
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*/
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merge_score = (break_score >> 16) & 0xFFFF;
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break_score = (break_score & 0xFFFF);
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if (!break_score)
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break_score = DEFAULT_BREAK_SCORE;
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if (!merge_score)
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merge_score = DEFAULT_MERGE_SCORE;
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DIFF_QUEUE_CLEAR(&outq);
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for (i = 0; i < q->nr; i++) {
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struct diff_filepair *p = q->queue[i];
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int score;
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/*
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* We deal only with in-place edit of blobs.
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* We do not break anything else.
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*/
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if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
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object_type(p->one->mode) == OBJ_BLOB &&
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object_type(p->two->mode) == OBJ_BLOB &&
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!strcmp(p->one->path, p->two->path)) {
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if (should_break(p->one, p->two,
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break_score, &score)) {
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/* Split this into delete and create */
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struct diff_filespec *null_one, *null_two;
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struct diff_filepair *dp;
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/* Set score to 0 for the pair that
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* needs to be merged back together
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* should they survive rename/copy.
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* Also we do not want to break very
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* small files.
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*/
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if (score < merge_score)
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score = 0;
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/* deletion of one */
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null_one = alloc_filespec(p->one->path);
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dp = diff_queue(&outq, p->one, null_one);
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dp->score = score;
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dp->broken_pair = 1;
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/* creation of two */
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null_two = alloc_filespec(p->two->path);
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dp = diff_queue(&outq, null_two, p->two);
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dp->score = score;
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dp->broken_pair = 1;
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diff_free_filespec_blob(p->one);
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diff_free_filespec_blob(p->two);
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free(p); /* not diff_free_filepair(), we are
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* reusing one and two here.
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*/
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continue;
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}
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}
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diff_free_filespec_data(p->one);
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diff_free_filespec_data(p->two);
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diff_q(&outq, p);
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}
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free(q->queue);
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*q = outq;
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return;
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}
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static void merge_broken(struct diff_filepair *p,
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struct diff_filepair *pp,
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struct diff_queue_struct *outq)
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{
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/* p and pp are broken pairs we want to merge */
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struct diff_filepair *c = p, *d = pp, *dp;
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if (DIFF_FILE_VALID(p->one)) {
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/* this must be a delete half */
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d = p; c = pp;
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}
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/* Sanity check */
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if (!DIFF_FILE_VALID(d->one))
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die("internal error in merge #1");
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if (DIFF_FILE_VALID(d->two))
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die("internal error in merge #2");
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if (DIFF_FILE_VALID(c->one))
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die("internal error in merge #3");
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if (!DIFF_FILE_VALID(c->two))
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die("internal error in merge #4");
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dp = diff_queue(outq, d->one, c->two);
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dp->score = p->score;
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diff_free_filespec_data(d->two);
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diff_free_filespec_data(c->one);
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free(d);
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free(c);
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}
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void diffcore_merge_broken(void)
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{
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struct diff_queue_struct *q = &diff_queued_diff;
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struct diff_queue_struct outq;
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int i, j;
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DIFF_QUEUE_CLEAR(&outq);
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for (i = 0; i < q->nr; i++) {
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struct diff_filepair *p = q->queue[i];
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if (!p)
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/* we already merged this with its peer */
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continue;
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else if (p->broken_pair &&
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!strcmp(p->one->path, p->two->path)) {
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/* If the peer also survived rename/copy, then
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* we merge them back together.
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*/
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for (j = i + 1; j < q->nr; j++) {
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struct diff_filepair *pp = q->queue[j];
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if (pp->broken_pair &&
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!strcmp(pp->one->path, pp->two->path) &&
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!strcmp(p->one->path, pp->two->path)) {
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/* Peer survived. Merge them */
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merge_broken(p, pp, &outq);
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q->queue[j] = NULL;
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break;
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}
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}
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if (q->nr <= j)
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/* The peer did not survive, so we keep
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* it in the output.
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*/
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diff_q(&outq, p);
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}
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else
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diff_q(&outq, p);
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}
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free(q->queue);
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*q = outq;
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return;
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}
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