Where can I get the source code of top?

["Kun Niu" <haoniukun%gmail.com@localhost>]

Dear all,
I'm trying to write a utility for system monitor.
My netbsd version is 3.1.
It needs to gather information about the system cpu usage data like
cpu load in user mode, system mode, idle task and so on.
On linux, I have the file "/proc/stat".
But I don't have it on netbsd.
However, I find that top can get the information I want.
So which file should I rely on on netbsd?
Or where can I get the source code of top for netbsd?
Thanks in advance for any hint.

Kun