X-Git-Url: https://git.verplant.org/?a=blobdiff_plain;f=merge-base.c;h=923256c821582f38daffed4fb0df2a97fe66d74b;hb=9d34c29db39bdb5c2443475dd6a24cfc5c2c9e37;hp=2ea44970d20500740db78b1cf0b9854c29e27553;hpb=3c249c950649a37f2871a8b193f01a0640a20aef;p=git.git

diff --git a/merge-base.c b/merge-base.c
index 2ea44970..923256c8 100644
--- a/merge-base.c
+++ b/merge-base.c
@@ -2,54 +2,127 @@
 #include "cache.h"
 #include "commit.h"
 
-static struct commit *process_list(struct commit_list **list_p, int this_mark,
-				   int other_mark)
-{
-	struct commit *item = (*list_p)->item;
+#define PARENT1 1
+#define PARENT2 2
+#define UNINTERESTING 4
 
-	if (item->object.flags & other_mark) {
-		return item;
-	} else {
-		pop_most_recent_commit(list_p, this_mark);
+static struct commit *interesting(struct commit_list *list)
+{
+	while (list) {
+		struct commit *commit = list->item;
+		list = list->next;
+		if (commit->object.flags & UNINTERESTING)
+			continue;
+		return commit;
 	}
 	return NULL;
 }
 
-struct commit *common_ancestor(struct commit *rev1, struct commit *rev2)
+/*
+ * A pathological example of how this thing works.
+ *
+ * Suppose we had this commit graph, where chronologically
+ * the timestamp on the commit are A <= B <= C <= D <= E <= F
+ * and we are trying to figure out the merge base for E and F
+ * commits.
+ *
+ *                  F
+ *                 / \
+ *            E   A   D
+ *             \ /   /  
+ *              B   /
+ *               \ /
+ *                C
+ *
+ * First we push E and F to list to be processed.  E gets bit 1
+ * and F gets bit 2.  The list becomes:
+ *
+ *     list=F(2) E(1), result=empty
+ *
+ * Then we pop F, the newest commit, from the list.  Its flag is 2.
+ * We scan its parents, mark them reachable from the side that F is
+ * reachable from, and push them to the list:
+ *
+ *     list=E(1) D(2) A(2), result=empty
+ *
+ * Next pop E and do the same.
+ *
+ *     list=D(2) B(1) A(2), result=empty
+ *
+ * Next pop D and do the same.
+ *
+ *     list=C(2) B(1) A(2), result=empty
+ *
+ * Next pop C and do the same.
+ *
+ *     list=B(1) A(2), result=empty
+ *
+ * Now it is B's turn.  We mark its parent, C, reachable from B's side,
+ * and push it to the list:
+ *
+ *     list=C(3) A(2), result=empty
+ *
+ * Now pop C and notice it has flags==3.  It is placed on the result list,
+ * and the list now contains:
+ *
+ *     list=A(2), result=C(3)
+ *
+ * We pop A and do the same.
+ * 
+ *     list=B(3), result=C(3)
+ *
+ * Next, we pop B and something very interesting happens.  It has flags==3
+ * so it is also placed on the result list, and its parents are marked
+ * uninteresting, retroactively, and placed back on the list:
+ *
+ *    list=C(7), result=C(7) B(3)
+ * 
+ * Now, list does not have any interesting commit.  So we find the newest
+ * commit from the result list that is not marked uninteresting.  Which is
+ * commit B.
+ */
+
+static struct commit *common_ancestor(struct commit *rev1, struct commit *rev2)
 {
-	struct commit_list *rev1list = NULL;
-	struct commit_list *rev2list = NULL;
+	struct commit_list *list = NULL;
+	struct commit_list *result = NULL;
 
-	commit_list_insert(rev1, &rev1list);
-	rev1->object.flags |= 0x1;
-	commit_list_insert(rev2, &rev2list);
-	rev2->object.flags |= 0x2;
+	if (rev1 == rev2)
+		return rev1;
 
 	parse_commit(rev1);
 	parse_commit(rev2);
 
-	while (rev1list || rev2list) {
-		struct commit *ret;
-		if (!rev1list) {
-			// process 2
-			ret = process_list(&rev2list, 0x2, 0x1);
-		} else if (!rev2list) {
-			// process 1
-			ret = process_list(&rev1list, 0x1, 0x2);
-		} else if (rev1list->item->date < rev2list->item->date) {
-			// process 2
-			ret = process_list(&rev2list, 0x2, 0x1);
-		} else {
-			// process 1
-			ret = process_list(&rev1list, 0x1, 0x2);
+	rev1->object.flags |= 1;
+	rev2->object.flags |= 2;
+	insert_by_date(rev1, &list);
+	insert_by_date(rev2, &list);
+
+	while (interesting(list)) {
+		struct commit *commit = list->item;
+		struct commit_list *tmp = list, *parents;
+		int flags = commit->object.flags & 7;
+
+		list = list->next;
+		free(tmp);
+		if (flags == 3) {
+			insert_by_date(commit, &result);
+
+			/* Mark children of a found merge uninteresting */
+			flags |= UNINTERESTING;
 		}
-		if (ret) {
-			free_commit_list(rev1list);
-			free_commit_list(rev2list);
-			return ret;
+		parents = commit->parents;
+		while (parents) {
+			struct commit *p = parents->item;
+			parents = parents->next;
+			if ((p->object.flags & flags) == flags)
+				continue;
+			parse_commit(p);
+			p->object.flags |= flags;
+			insert_by_date(p, &list);
 		}
 	}
-	return NULL;
+	return interesting(result);
 }
 
 int main(int argc, char **argv)
@@ -60,10 +133,12 @@ int main(int argc, char **argv)
 	if (argc != 3 ||
 	    get_sha1(argv[1], rev1key) ||
 	    get_sha1(argv[2], rev2key)) {
-		usage("merge-base <commit-id> <commit-id>");
+		usage("git-merge-base <commit-id> <commit-id>");
 	}
-	rev1 = lookup_commit(rev1key);
-	rev2 = lookup_commit(rev2key);
+	rev1 = lookup_commit_reference(rev1key);
+	rev2 = lookup_commit_reference(rev2key);
+	if (!rev1 || !rev2)
+		return 1;
 	ret = common_ancestor(rev1, rev2);
 	if (!ret)
 		return 1;