On Wed, Oct 22, 2014 at 10:03 AM, Niels Möller nisse@lysator.liu.se wrote:
I think I will leave the curve25519 and eddsa code for now, even though there are several important optimizations left to do (see the just updated http://www.lysator.liu.se/~nisse/nettle/plan.html). I think it's getting time to do fat binaries. To make progress, I think it's best to start with something simple, relying on __attribute__((constructor) and/or __attribute__(ifunc ...)). For the case of memxor (where on x86_64, the fat binary mechanism needs to select between sse2 and non-sse2 code), I'm also considering some reorganization:
- Use smaller assembly routines doing one case each, and let the main entry point always be C code which can sort out the different cases and handle bytes at the beginning and end of the buffer.
- Fix the cases where the current current code reads a few bytes outside of input buffers (but luckily without crossing word boundaries, iirc).
- Add some internal entry points, for cases where alignment is known by the caller.
That would really be great news, and would be a very good incentive to port gnutls to nettle 3.x. If I could add to that list, I think that simplicity of 3rd party enhancements to that fat binary is also significant, as I believe you'd like to rely on others doing these optimizations for their CPU types.
regards, Nikos