Where's the source code for __builtin__?

[Dustan]

I've been paging through the source code for various C modules in
python, and wanted to find the source of some of the builtin
functions. I searched through the Modules, Objects, Python, and Parser
folder, searched docs.python.org, searched the archived messages of
this group, searched the web, and got absolutely nowhere in finding a
__builtin__.c, or anything that contains the builtin source code.

Help?