Provide bn_mod_add_words() and bn_mod_sub_words() on amd64.

These use s2n-bignum's bignum_modadd() and bignum_modsub() routines.

ok tb@

2 files changed, 25 insertions, 2 deletions

diff --git a/src/lib/libcrypto/bn/arch/amd64/bn_arch.c b/src/lib/libcrypto/bn/arch/amd64/bn_arch.c
index 38a4350d17..97dc7b90c7 100644
--- a/src/lib/libcrypto/bn/arch/amd64/bn_arch.c
+++ b/src/lib/libcrypto/bn/arch/amd64/bn_arch.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_arch.c,v 1.9 2025/08/12 10:00:40 jsing Exp $ */
+/*      $OpenBSD: bn_arch.c,v 1.10 2025/08/14 15:17:19 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -60,6 +60,26 @@ bn_sub_words(BN_ULONG *rd, const BN_ULONG *ad, const BN_ULONG *bd, int n)
 }
 #endif
 
+#ifdef HAVE_BN_MOD_ADD_WORDS
+void
+bn_mod_add_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+    const BN_ULONG *m, size_t n)
+{
+        bignum_modadd(n, (uint64_t *)r, (const uint64_t *)a,
+            (const uint64_t *)b, (const uint64_t *)m);
+}
+#endif
+
+#ifdef HAVE_BN_MOD_SUB_WORDS
+void
+bn_mod_sub_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+    const BN_ULONG *m, size_t n)
+{
+        bignum_modsub(n, (uint64_t *)r, (const uint64_t *)a,
+            (const uint64_t *)b, (const uint64_t *)m);
+}
+#endif
+
 #ifdef HAVE_BN_MUL_ADD_WORDS
 BN_ULONG
 bn_mul_add_words(BN_ULONG *rd, const BN_ULONG *ad, int num, BN_ULONG w)
diff --git a/src/lib/libcrypto/bn/arch/amd64/bn_arch.h b/src/lib/libcrypto/bn/arch/amd64/bn_arch.h
index 927cd75208..d07a898b80 100644
--- a/src/lib/libcrypto/bn/arch/amd64/bn_arch.h
+++ b/src/lib/libcrypto/bn/arch/amd64/bn_arch.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_arch.h,v 1.14 2024/03/26 06:09:25 jsing Exp $ */
+/*      $OpenBSD: bn_arch.h,v 1.15 2025/08/14 15:17:19 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -27,6 +27,9 @@
 
 #define HAVE_BN_DIV_WORDS
 
+#define HAVE_BN_MOD_ADD_WORDS
+#define HAVE_BN_MOD_SUB_WORDS
+
 #define HAVE_BN_MUL_ADD_WORDS
 #define HAVE_BN_MUL_COMBA4
 #define HAVE_BN_MUL_COMBA8