public void unpop(RevCommit c) {Block b = head;if (b == null) {b = free.newBlock();b.resetToMiddle();b.add(c);head = b;tail = b;return;} else if (b.canUnpop()) {b.unpop(c);return;}b = free.newBlock();b.resetToEnd();b.unpop(c);b.next = head;head = b;}