combine-diff: update --cc "uninteresting hunks" logic.

Earlier logic was discarding hunks that has difference from only
one parent or the same difference from all but one parent.  This
changes it to check if the differences on all lines are from the
same sets of parents.  This discards more uninteresting hunks
and seems to match expectations more naturally.

Signed-off-by: Junio C Hamano <junkio@cox.net>

combine-diff.c

@@ -262,58 +262,6 @@ static int interesting(struct sline *sline, unsigned long all_mask)
 	return ((sline->flag & all_mask) != all_mask || sline->lost_head);
 }
 
-static unsigned long line_common_diff(struct sline *sline, unsigned long all_mask)
-{
-	/*
-	 * Look at the line and see from which parents we have the
-	 * same difference.
-	 */
-
-	/* Lower bits of sline->flag records if the parent had this
-	 * line, so XOR with all_mask gives us on-bits for parents we
-	 * have differences with.
-	 */
-	unsigned long common_adds = (sline->flag ^ all_mask) & all_mask;
-	unsigned long common_removes = all_mask;
-
-	/* If all the parents have this line, that also counts as
-	 * having the same difference.
-	 */
-	if (!common_adds)
-		common_adds = all_mask;
-
-	if (sline->lost_head) {
-		/* Lost head list records the lines removed from
-		 * the parents, and parent_map records from which
-		 * parent the line was removed.
-		 */
-		struct lline *ll;
-		for (ll = sline->lost_head; ll; ll = ll->next) {
-			common_removes &= ll->parent_map;
-		}
-	}
-	return common_adds & common_removes;
-}
-
-static unsigned long line_all_diff(struct sline *sline, unsigned long all_mask)
-{
-	/*
-	 * Look at the line and see from which parents we have some difference.
-	 */
-	unsigned long different = (sline->flag ^ all_mask) & all_mask;
-	if (sline->lost_head) {
-		/* Lost head list records the lines removed from
-		 * the parents, and parent_map records from which
-		 * parent the line was removed.
-		 */
-		struct lline *ll;
-		for (ll = sline->lost_head; ll; ll = ll->next) {
-			different |= ll->parent_map;
-		}
-	}
-	return different;
-}
-
 static unsigned long adjust_hunk_tail(struct sline *sline,
 				      unsigned long all_mask,
 				      unsigned long hunk_begin,
@@ -417,8 +365,7 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
 	i = 0;
 	while (i < cnt) {
 		unsigned long j, hunk_begin, hunk_end;
-		int same, diff;
-		unsigned long same_diff, all_diff;
+		unsigned long same_diff;
 		while (i < cnt && !(sline[i].flag & mark))
 			i++;
 		if (cnt <= i)
@@ -449,23 +396,40 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
 		}
 		hunk_end = j;
 
-		/* [i..hunk_end) are interesting.  Now does it have
-		 * the same change with all but one parent?
+		/* [i..hunk_end) are interesting.  Now is it really
+		 * interesting?
 		 */
-		same_diff = all_mask;
-		all_diff = 0;
-		for (j = i; j < hunk_end; j++) {
-			same_diff &= line_common_diff(sline + j, all_mask);
-			all_diff |= line_all_diff(sline + j, all_mask);
+		same_diff = 0;
+		has_interesting = 0;
+		for (j = i; j < hunk_end && !has_interesting; j++) {
+			unsigned long this_diff = ~sline[j].flag & all_mask;
+			struct lline *ll = sline[j].lost_head;
+			if (this_diff) {
+				/* This has some changes.  Is it the
+				 * same as others?
+				 */
+				if (!same_diff)
+					same_diff = this_diff;
+				else if (same_diff != this_diff) {
+					has_interesting = 1;
+					break;
 				}
-		diff = same = 0;
-		for (j = 0; j < num_parent; j++) {
-			if (same_diff & (1UL<<j))
-				same++;
-			if (all_diff & (1UL<<j))
-				diff++;
 			}
-		if ((num_parent - 1 <= same) || (diff == 1)) {
+			while (ll && !has_interesting) {
+				/* Lost this line from these parents;
+				 * who are they?  Are they the same?
+				 */
+				this_diff = ll->parent_map;
+				if (!same_diff)
+					same_diff = this_diff;
+				else if (same_diff != this_diff) {
+					has_interesting = 1;
+				}
+				ll = ll->next;
+			}
+		}
+
+		if (!has_interesting) {
 			/* This hunk is not that interesting after all */
 			for (j = hunk_begin; j < hunk_end; j++)
 				sline[j].flag &= ~mark;