gistfile1.cs

    public static class LinkedListHelperExtensions {
        public static LinkedListNode<T> FindFirstBefore<T>(this LinkedListNode<T> thisNode, bool searchThisNode, Func<T, bool> predicate) {
            LinkedListNode<T> currentNode = (searchThisNode ? thisNode : thisNode.Previous);

            while (currentNode != null) {
                if (predicate(currentNode.Value)) {
                    break;
                }
                currentNode = currentNode.Previous;
            }

            return currentNode;
        }
    }