I see. Well, I'm no expert on this, but I can point you to a couple of open-source implementations of libc. Here you can find the math functions not specific to a platform (if I understand correctly):
The platform-dependant implementations of log and exp can be found in the sysdeps directory. Look for the fpu directory under each of the platform directories.
You can also get a local copy of the whole library for easier access:
I hope this helps.