Provide optimised bn_mulw() for riscv64.

This provides a 1.5-2x performance gain for BN multiplication, with a
similar improvement being seen for RSA operations.

1 files changed, 11 insertions, 7 deletions

diff --git a/src/lib/libcrypto/bn/arch/riscv64/bn_arch.h b/src/lib/libcrypto/bn/arch/riscv64/bn_arch.h
index 354774cde3..66256acad0 100644
--- a/src/lib/libcrypto/bn/arch/riscv64/bn_arch.h
+++ b/src/lib/libcrypto/bn/arch/riscv64/bn_arch.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_arch.h,v 1.4 2023/02/16 10:41:03 jsing Exp $ */
+/*      $OpenBSD: bn_arch.h,v 1.5 2023/07/07 16:10:32 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -15,15 +15,17 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <openssl/bn.h>
+
 #ifndef HEADER_BN_ARCH_H
 #define HEADER_BN_ARCH_H
 
 #ifndef OPENSSL_NO_ASM
 
-#if 0 /* Needs testing and enabling. */
 #if defined(__GNUC__)
-#define 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)
 {
@@ -34,15 +36,17 @@ bn_mulw(BN_ULONG a, BN_ULONG b, BN_ULONG *out_r1, BN_ULONG *out_r0)
          * of these instructions is important, as they can potentially be fused
          * into a single operation.
          */
-        __asm__ ("mulh %0, %2, %3; mul %1, %2, %3"
-            : "=&r"(r1), "=r"(r0)
-            : "r"(a), "r"(b));
+        __asm__ (
+            "mulhu %[r1], %[a], %[b] \n"
+            "mul   %[r0], %[a], %[b] \n"
+            : [r1]"=&r"(r1), [r0]"=r"(r0)
+            : [a]"r"(a), [b]"r"(b));
 
         *out_r1 = r1;
         *out_r0 = r0;
 }
+
 #endif /* __GNUC__ */
-#endif
 
 #endif
 #endif