Provide and use bn_clzw() in place of bn_word_clz().

On some architectures, we can provide an optimised (often single
instruction) count-leading-zero implementation. In order to do this
effectively, provide bn_clzw() as a static inline that can be replaced
by an architecture specific version. The default implementation defers
to the bn_word_clz() function (which may also be architecture specific).

ok tb@

1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bn/bn_internal.h b/src/lib/libcrypto/bn/bn_internal.h
index f5c69c5d77..b712b736f6 100644
--- a/src/lib/libcrypto/bn/bn_internal.h
+++ b/src/lib/libcrypto/bn/bn_internal.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bn_internal.h,v 1.13 2023/06/21 07:41:55 jsing Exp $ */
+/*      $OpenBSD: bn_internal.h,v 1.14 2023/06/21 07:48:41 jsing Exp $ */
 /*
  * Copyright (c) 2023 Joel Sing <jsing@openbsd.org>
  *
@@ -58,6 +58,14 @@ bn_ct_eq_zero_mask(BN_ULONG w)
 }
 #endif
 
+#ifndef HAVE_BN_CLZW
+static inline int
+bn_clzw(BN_ULONG w)
+{
+        return bn_word_clz(w);
+}
+#endif
+
 /*
  * Big number primitives are named as the operation followed by a suffix
  * that indicates the number of words that it operates on, where 'w' means