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#include <stdlib.h>
#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;
	
	if (item->object.flags & this_mark) {
		/*
		  printf("%d already seen %s %x\n",
		  this_mark
		  sha1_to_hex(posn->parent->sha1),
		  posn->parent->flags);
		*/
		/* do nothing; this indicates that this side
		 * split and reformed, and we only need to
		 * mark it once.
		 */
		*list_p = (*list_p)->next;
	} else if (item->object.flags & other_mark) {
		return item;
	} else {
		/*
		  printf("%d based on %s\n",
		  this_mark,
		  sha1_to_hex(posn->parent->sha1));
		*/
		pop_most_recent_commit(list_p);
		item->object.flags |= this_mark;
	}
	return NULL;
}

struct commit *common_ancestor(struct commit *rev1, struct commit *rev2)
{
	struct commit_list *rev1list = NULL;
	struct commit_list *rev2list = NULL;

	commit_list_insert(rev1, &rev1list);
	commit_list_insert(rev2, &rev2list);

	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);
		}
		if (ret) {
			free_commit_list(rev1list);
			free_commit_list(rev2list);
			return ret;
		}
	}
	return NULL;
}

int main(int argc, char **argv)
{
	struct commit *rev1, *rev2, *ret;
	unsigned char rev1key[20], rev2key[20];

	if (argc != 3 ||
	    get_sha1_hex(argv[1], rev1key) ||
	    get_sha1_hex(argv[2], rev2key)) {
		usage("merge-base <commit-id> <commit-id>");
	}
	rev1 = lookup_commit(rev1key);
	rev2 = lookup_commit(rev2key);
	ret = common_ancestor(rev1, rev2);
	if (!ret)
		return 1;
	printf("%s\n", sha1_to_hex(ret->object.sha1));
	return 0;
}