Overhead when using a C library

[Jeremy DeHaan]

Hey guys!

I am working on a binding for D, and am almost finished! I 
started to think of some things I might like to work on to 
improve the binding after I get everything working, and one of 
the things I thought of was rewriting certain parts to use only D 
code instead of making calls to the C functions. Is there any 
kind of performance overhead in using C libraries to interact 
with your D program? If it isn't going to offer much performance 
gain then I probably don't need to bother writing extra code.

Thanks as usual!