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Message-ID: <2ECD48ACEA9540C083E6B797CFD18027@H270>
From: "Stefan Kanthak" <stefan.kanthak@nexgo.de>
To: "Eric Biggers" <ebiggers@kernel.org>,
	<linux-crypto@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
References: <20240411162359.39073-1-ebiggers@kernel.org> <20240411162359.39073-5-ebiggers@kernel.org>
In-Reply-To: <20240411162359.39073-5-ebiggers@kernel.org>
Subject: Re: [PATCH v2 4/4] crypto: x86/sha256-ni - simplify do_4rounds
Date: Mon, 15 Apr 2024 22:41:07 +0200
Organization: Me, myself & IT
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"Eric Biggers" <ebiggers@kernel.org> wrote:

> Instead of loading the message words into both MSG and \m0 and then
> adding the round constants to MSG, load the message words into \m0 and
> the round constants into MSG and then add \m0 to MSG.  This shortens the
> source code slightly.  It changes the instructions slightly, but it
> doesn't affect binary code size and doesn't seem to affect performance.

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

Now that all code written by Tim Chen and Sean Gulley is gone,
remove their copyright notice and insert your and my name instead.

regards
Stefan

PS: see <https://skanthak.homepage.t-online.de/fips-180.html>
    (which I still polish) not just for this implementation.

PPS: if MASM had a counter like \@, I'd used it there.