Well, there is always Lisp: http://psg.com/~dlamkins/sl/chapter18.html http://psg.com/~dlamkins/sl/chapter18.html At least SBCL will generate efficient machin

Well, there is always Lisp: http://psg.com/~dlamkins/sl/chapter18.html http://psg.com/~dlamkins/sl/chapter18.html At least SBCL will generate efficient machine language for bit vector manipulations if you tell it the sizes of the vectors (or if it can infer that information). It might just be a matter of opinion, but I would say that Lisp beats the pants off C in terms of programming; you are almost never going to have to keep track of pointers or memory allocations, you have far less undefined behavior to deal with, and it is generally a more expressive language. SBCL and CMUCL also support a non-standard feature that is similar to inline assembly language in C, the VOP system, that allows you to utilize obscure instructions or change how your code will be generated, if there is some reason for doing that (e.g. if your encryption library will use AESNI). Of course, since you said "library," I assume you meant for this to be used in other programs, possibly programs not written in Lisp. Unfortunately, SBCL's support for that is still rough; commercial Lisp compilers may have better support for it. Of course, if you were targeting an OS written in Lisp, things would probably be different -- my view is that C's popularity is mostly a result of how many systems were written in C i.e. how much legacy code there is, and that were it not for that momentum C would be written off as an inexpressive and difficult to work with language.