+int handle_revision_arg(const char *arg, struct rev_info *revs,
+ int flags,
+ int cant_be_filename)
+{
+ char *dotdot;
+ struct object *object;
+ unsigned char sha1[20];
+ int local_flags;
+
+ dotdot = strstr(arg, "..");
+ if (dotdot) {
+ unsigned char from_sha1[20];
+ const char *next = dotdot + 2;
+ const char *this = arg;
+ int symmetric = *next == '.';
+ unsigned int flags_exclude = flags ^ UNINTERESTING;
+
+ *dotdot = 0;
+ next += symmetric;
+
+ if (!*next)
+ next = "HEAD";
+ if (dotdot == arg)
+ this = "HEAD";
+ if (!get_sha1(this, from_sha1) &&
+ !get_sha1(next, sha1)) {
+ struct commit *a, *b;
+ struct commit_list *exclude;
+
+ a = lookup_commit_reference(from_sha1);
+ b = lookup_commit_reference(sha1);
+ if (!a || !b) {
+ die(symmetric ?
+ "Invalid symmetric difference expression %s...%s" :
+ "Invalid revision range %s..%s",
+ arg, next);
+ }
+
+ if (!cant_be_filename) {
+ *dotdot = '.';
+ verify_non_filename(revs->prefix, arg);
+ }
+
+ if (symmetric) {
+ exclude = get_merge_bases(a, b, 1);
+ add_pending_commit_list(revs, exclude,
+ flags_exclude);
+ free_commit_list(exclude);
+ a->object.flags |= flags;
+ } else
+ a->object.flags |= flags_exclude;
+ b->object.flags |= flags;
+ add_pending_object(revs, &a->object, this);
+ add_pending_object(revs, &b->object, next);
+ return 0;
+ }
+ *dotdot = '.';
+ }
+ dotdot = strstr(arg, "^@");
+ if (dotdot && !dotdot[2]) {
+ *dotdot = 0;
+ if (add_parents_only(revs, arg, flags))
+ return 0;
+ *dotdot = '^';
+ }
+ local_flags = 0;
+ if (*arg == '^') {
+ local_flags = UNINTERESTING;
+ arg++;
+ }
+ if (get_sha1(arg, sha1))
+ return -1;
+ if (!cant_be_filename)
+ verify_non_filename(revs->prefix, arg);
+ object = get_reference(revs, arg, sha1, flags ^ local_flags);
+ add_pending_object(revs, object, arg);
+ return 0;
+}
+