From cdcc651948fa49d18040b9e23f960d64e97f1eda Mon Sep 17 00:00:00 2001
From: Joel Sing <jsing@cvs.openbsd.org>
Date: Sun, 25 Jun 2023 11:42:27 +0000
Subject: Provide additional BN primitives for BN_ULLONG architectures.

On BN_ULLONG architectures, the C compiler can usually do a decent job
of optimising primitives, however it struggles to see through primitive
calls due to type narrowing. As such, providing explicit versions of
compound primitives can result in the production of more optimal code.
For example, on arm the bn_mulw_addw_addw() primitive can be replaced
with a single umaal instruction, which provides significant performance
gains.

Rather than intermingling #ifdef/#else throughout the header, the
BN_ULLONG defines are pulled up above the normal functions. This also
allows complex compound primitives to be reused. The conditionals have also
been changed from BN_LLONG to BN_ULLONG, since that is what really matters.

ok tb@
---
 lib/libcrypto/bn/bn_internal.h | 100 ++++++++++++++++++++++++++++++++---------
 1 file changed, 79 insertions(+), 21 deletions(-)

(limited to 'lib')

diff --git a/lib/libcrypto/bn/bn_internal.h b/lib/libcrypto/bn/bn_internal.h
index b712b736f6a..fd04bc9f8aa 100644
--- a/lib/libcrypto/bn/bn_internal.h
+++ b/lib/libcrypto/bn/bn_internal.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bn_internal.h,v 1.14 2023/06/21 07:48:41 jsing Exp $ */
+/*	$OpenBSD: bn_internal.h,v 1.15 2023/06/25 11:42:26 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -80,12 +80,18 @@ bn_clzw(BN_ULONG w)
  */
 
 /*
- * bn_addw() computes (r1:r0) = a + b, where both inputs are single words,
- * producing a double word result. The value of r1 is the carry from the
- * addition.
+ * Default implementations for BN_ULLONG architectures.
+ *
+ * On these platforms the C compiler is generally better at optimising without
+ * the use of inline assembly primitives. However, it can be difficult for the
+ * compiler to see through primitives in order to combine operations, due to
+ * type changes/narrowing. For this reason compound primitives are usually
+ * explicitly provided.
  */
+#ifdef BN_ULLONG
+
 #ifndef HAVE_BN_ADDW
-#ifdef BN_LLONG
+#define HAVE_BN_ADDW
 static inline void
 bn_addw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
 {
@@ -96,8 +102,75 @@ bn_addw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
 	*out_r1 = r >> BN_BITS2;
 	*out_r0 = r & BN_MASK2;
 }
-#else
+#endif
+
+#ifndef HAVE_BN_ADDW_ADDW
+#define HAVE_BN_ADDW_ADDW
+static inline void
+bn_addw_addw(BN_ULONG a, BN_ULONG b, BN_ULONG c, BN_ULONG *out_r1,
+    BN_ULONG *out_r0)
+{
+	BN_ULLONG r;
+
+	r = (BN_ULLONG)a + (BN_ULLONG)b + (BN_ULLONG)c;
+
+	*out_r1 = r >> BN_BITS2;
+	*out_r0 = r & BN_MASK2;
+}
+#endif
+
+#ifndef HAVE_BN_MULW
+#define HAVE_BN_MULW
+static inline void
+bn_mulw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
+{
+	BN_ULLONG r;
+
+	r = (BN_ULLONG)a * (BN_ULLONG)b;
+
+	*out_r1 = r >> BN_BITS2;
+	*out_r0 = r & BN_MASK2;
+}
+#endif
+
+#ifndef HAVE_BN_MULW_ADDW
+#define HAVE_BN_MULW_ADDW
+static inline void
+bn_mulw_addw(BN_ULONG a, BN_ULONG b, BN_ULONG c, BN_ULONG *out_r1,
+    BN_ULONG *out_r0)
+{
+	BN_ULLONG r;
+
+	r = (BN_ULLONG)a * (BN_ULLONG)b + (BN_ULLONG)c;
+
+	*out_r1 = r >> BN_BITS2;
+	*out_r0 = r & BN_MASK2;
+}
+#endif
 
+#ifndef HAVE_BN_MULW_ADDW_ADDW
+#define HAVE_BN_MULW_ADDW_ADDW
+static inline void
+bn_mulw_addw_addw(BN_ULONG a, BN_ULONG b, BN_ULONG c, BN_ULONG d,
+    BN_ULONG *out_r1, BN_ULONG *out_r0)
+{
+	BN_ULLONG r;
+
+	r = (BN_ULLONG)a * (BN_ULLONG)b + (BN_ULLONG)c + (BN_ULLONG)d;
+
+	*out_r1 = r >> BN_BITS2;
+	*out_r0 = r & BN_MASK2;
+}
+#endif
+
+#endif /* !BN_ULLONG */
+
+/*
+ * bn_addw() computes (r1:r0) = a + b, where both inputs are single words,
+ * producing a double word result. The value of r1 is the carry from the
+ * addition.
+ */
+#ifndef HAVE_BN_ADDW
 static inline void
 bn_addw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
 {
@@ -112,7 +185,6 @@ bn_addw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
 	*out_r0 = r0;
 }
 #endif
-#endif
 
 /*
  * bn_addw_addw() computes (r1:r0) = a + b + c, where all inputs are single
@@ -230,19 +302,6 @@ bn_qwsubqw(BN_ULONG a3, BN_ULONG a2, BN_ULONG a1, BN_ULONG a0, BN_ULONG b3,
  * producing a double word result.
  */
 #ifndef HAVE_BN_MULW
-#ifdef BN_LLONG
-static inline void
-bn_mulw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
-{
-	BN_ULLONG r;
-
-	r = (BN_ULLONG)a * (BN_ULLONG)b;
-
-	*out_r1 = r >> BN_BITS2;
-	*out_r0 = r & BN_MASK2;
-}
-
-#else /* !BN_LLONG */
 /*
  * Multiply two words (a * b) producing a double word result (h:l).
  *
@@ -339,7 +398,6 @@ bn_mulw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
 	*out_r0 = (acc1 << BN_BITS4) | acc0;
 }
 #endif
-#endif /* !BN_LLONG */
 #endif
 
 #ifndef HAVE_BN_MULW_LO
-- 
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