Looks ok to me.
I am left wondering if the code should just do that
add32_with_carry3(sum, result >> 32, result);
in the caller instead - right now pretty much every return point in
do_csum() effectively does that, with the exception of
- the 0-length case, which is presumably not really an issue in real
life and could as well just return 0
- the 8-byte case that does two 32-bit loads instead, but could just
do a single 8-byte load and return it (and then the generic version in
the caller would do a shift).
That would simplifiy the code a bit - it wouldn't need to pass in
"sum" to do_csum at all, and we'd have just a single case of that
special 3-input carry add..
But I'm certainly ok with it as-is. I'm not sure how performance
critical the whole csum routine is, but at least now it doesn't
introduce a lot of new complex asm.
And this version might be reasonable to make generic, so that non-x86
architectures could use the same approach. That's what we ended up
doing for the dcache word-at-a-time code too in the end.
Linus
