Provide bn_div_rem_words() and make use of it.

Provide a function that divides a double word (h:l) by d, returning the
quotient q and the remainder r, such that q * d + r is equal to the
numerator. Call this from the three places that currently implement this
themselves.

This is implemented with some slight indirection, which allows for per
architecture implementations, replacing the define/macro tangle, which
messes with variables that are not passed to it.

Also remove a duplicate of bn_div_words() for the BN_ULLONG && BN_DIV2W
case - this is already handled.

ok tb@

2 files changed, 52 insertions, 2 deletions

diff --git a/src/lib/libcrypto/bn/arch/amd64/bn_arch.h b/src/lib/libcrypto/bn/arch/amd64/bn_arch.h
index 065f6b1c3b..6b7eaf5eee 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 1.7 2023/01/23 12:17:57 jsing Exp $ */
+/*      $OpenBSD: bn_arch.h,v 1.8 2023/01/28 16:33:34 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -15,6 +15,8 @@
  * 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
 
@@ -36,5 +38,28 @@
 
 #define HAVE_BN_SUB_WORDS
 
+#if defined(__GNUC__)
+#define HAVE_BN_DIV_REM_WORDS_INLINE
+
+static inline void
+bn_div_rem_words_inline(BN_ULONG h, BN_ULONG l, BN_ULONG d, BN_ULONG *out_q,
+    BN_ULONG *out_r)
+{
+        BN_ULONG q, r;
+
+        /*
+         * Unsigned division of %rdx:%rax by d with quotient being stored in
+         * %rax and remainder in %rdx.
+         */
+        __asm__ volatile ("divq %4"
+            : "=a"(q), "=d"(r)
+            : "d"(h), "a"(l), "rm"(d)
+            : "cc");
+
+        *out_q = q;
+        *out_r = r;
+}
+#endif /* __GNUC__ */
+
 #endif
 #endif
diff --git a/src/lib/libcrypto/bn/arch/i386/bn_arch.h b/src/lib/libcrypto/bn/arch/i386/bn_arch.h
index 681c2090a7..e2b4957efc 100644
--- a/src/lib/libcrypto/bn/arch/i386/bn_arch.h
+++ b/src/lib/libcrypto/bn/arch/i386/bn_arch.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_arch.h,v 1.6 2023/01/23 12:17:57 jsing Exp $ */
+/*      $OpenBSD: bn_arch.h,v 1.7 2023/01/28 16:33:34 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -15,6 +15,8 @@
  * 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
 
@@ -35,5 +37,28 @@
 
 #define HAVE_BN_SUB_WORDS
 
+#if defined(__GNUC__)
+#define HAVE_BN_DIV_REM_WORDS_INLINE
+
+static inline void
+bn_div_rem_words_inline(BN_ULONG h, BN_ULONG l, BN_ULONG d, BN_ULONG *out_q,
+    BN_ULONG *out_r)
+{
+        BN_ULONG q, r;
+
+        /*
+         * Unsigned division of %edx:%eax by d with quotient being stored in
+         * %eax and remainder in %edx.
+         */
+        __asm__ volatile ("divl %4"
+            : "=a"(q), "=d"(r)
+            : "a"(l), "d"(h), "rm"(d)
+            : "cc");
+
+        *out_q = q;
+        *out_r = r;
+}
+#endif /* __GNUC__ */
+
 #endif
 #endif