Post with choice : sidebar options

Hello,

I’m trying to create my theme, and I learn slowly.

But I have a problem.

I would like to have, for posts, sidebar options in the posts admin :
– no sidebar.
– left sidebar.
– right sidebar.
– both sidebars.

In fact, as for pages with the page templates, but for the posts.

I saw this in several themes, but I don’t find how to do this.

(I don’t want to use plugin).

if you have any advice or links to do this, it would be great
Thanks.
(sorry for my english)