1 files changed, 294 insertions, 0 deletions

diff --git a/diffcore-break.c b/diffcore-break.c
new file mode 100644
index 0000000..44f8678
--- /dev/null
+++ b/diffcore-break.c
@@ -0,0 +1,294 @@
+/*
+ * 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, 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 */
+
+	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,
+				   &src->cnt_data, &dst->cnt_data,
+				   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;
+
+	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(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;
+	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;
+}