Where can i find the code of the glRotatef function ?
http://mesa3d.sourceforge.net/
http://oss.sgi.com/projects/ogl-sample/index.html
The first one is Mesa, the OpenGL software implementation for Linux. The second one is the reference implementation by Sun.
But if you only want to know how to calculate a rotation matrix, there is an appendix in the Redbook with the matrices that are generated by the transformation functions. It’s available here:
http://www.opengl.org/documentation/red_book_1.0/