Re: [PATCH v2 4/4] crypto: x86/sha256-ni - simplify do_4rounds

[Eric Biggers]

On Tue, Apr 16, 2024 at 12:04:56AM +0200, Stefan Kanthak wrote:
> "Eric Biggers" <ebiggers@xxxxxxxxxx> wrote:
> 
> > On Mon, Apr 15, 2024 at 10:41:07PM +0200, Stefan Kanthak wrote:
> [...]
> >> At last the final change: write the macro straightforward and SIMPLE,
> >> closely matching NIST.FIPS.180-4.pdf and their order of operations.
> >> 
> >> @@ ...
> >> +.macro  sha256  m0 :req, m1 :req, m2 :req, m3 :req
> >> +.if \@ < 4
> >> +        movdqu  \@*16(DATA_PTR), \m0
> >> +        pshufb  SHUF_MASK, \m0          # \m0 = {w(\@*16), w(\@*16+1), w(\@*16+2), w(\@*16+3)}
> >> +.else
> >> +                                        # \m0 = {w(\@*16-16), w(\@*16-15), w(\@*16-14), w(\@*16-13)}
> >> +                                        # \m1 = {w(\@*16-12), w(\@*16-11), w(\@*16-10), w(\@*16-9)}
> >> +                                        # \m2 = {w(\@*16-8),  w(\@*16-7),  w(\@*16-6),  w(\@*16-5)}
> >> +                                        # \m3 = {w(\@*16-4),  w(\@*16-3),  w(\@*16-2),  w(\@*16-1)}
> >> +        sha256msg1 \m1, \m0
> >> +        movdqa     \m3, TMP
> >> +        palignr    $4, \m2, TMP
> >> +        paddd      TMP, \m0
> >> +        sha256msg2 \m3, \m0             # \m0 = {w(\@*16), w(\@*16+1), w(\@*16+2), w(\@*16+3)}
> >> +.endif
> >> +        movdqa      (\@-8)*16(SHA256CONSTANTS), MSG
> >> +        paddd       \m0, MSG
> >> +        sha256rnds2 STATE0, STATE1      # STATE1 = {f', e', b', a'}
> >> +        punpckhqdq  MSG, MSG
> >> +        sha256rnds2 STATE1, STATE0      # STATE0 = {f", e", b", a"},
> >> +                                        # STATE1 = {h", g", d", c"}
> >> +.endm
> >> 
> >> JFTR: you may simplify this further using .altmacro and generate \m0 to \m3
> >>       as MSG%(4-\@&3), MSG%(5-\@&3), MSG%(6-\@&3) and MSG%(7-\@&3) within
> >>       the macro, thus getting rid of its 4 arguments.
> >> 
> >> @@ ...
> >> +.rept 4                                 # 4*4*4 rounds
> >> +        sha256  MSG0, MSG1, MSG2, MSG3
> >> +        sha256  MSG1, MSG2, MSG3, MSG0
> >> +        sha256  MSG2, MSG3, MSG0, MSG1
> >> +        sha256  MSG3, MSG0, MSG1, MSG2
> >> +.endr
> > 
> > Could you please send a real patch, following
> > Documentation/process/submitting-patches.rst?  It's hard to understand what
> > you're proposing here.
> 
> 1) I replace your macro (which unfortunately follows Tim Chens twisted code)
>    COMPLETELY with a clean and simple implementation: message schedule first,
>    update of state variables last.
>    You don't need ".if \i >= 12 && \i < 60"/".if \i >= 4 && \i < 52" at all!

It's probably intentional that the code does the message schedule computations a
bit ahead of time.  This might improve performance by reducing the time spent
waiting for the message schedule.

It would be worth trying a few different variants on different CPUs and seeing
how they actually perform in practice, though.

> 
> 2) I replace the .irp which invokes your macro with a .rept: my macro uses \@
>    instead of an argument for the round number.
> 
> <https://sourceware.org/binutils/docs/as.html#Macro>

The \@ feature is a bit obscure and maybe is best avoided.

- Eric