Provide and use bn_copy_words() in BN_copy().

This is simpler than the current code, while still being well optimised by
compilers, across a range of architectures. In many cases we even get a
performance gain for the BN sizes that we primarily care about.

Joint work with tb@

diff --git a/lib/libcrypto/bn/bn_lib.c b/lib/libcrypto/bn/bn_lib.c
index 3ca2b7f..f25caa0 100644 (file)
--- a/lib/libcrypto/bn/bn_lib.c
+++ b/lib/libcrypto/bn/bn_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_lib.c,v 1.80 2023/04/01 12:44:56 tb Exp $ */
+/* $OpenBSD: bn_lib.c,v 1.81 2023/04/14 11:04:24 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -344,50 +344,34 @@ BN_dup(const BIGNUM *a)
        return t;
 }
 
+static inline void
+bn_copy_words(BN_ULONG *ap, const BN_ULONG *bp, int n)
+{
+       while (n > 0) {
+               ap[0] = bp[0];
+               ap++;
+               bp++;
+               n--;
+       }
+}
+
 BIGNUM *
 BN_copy(BIGNUM *a, const BIGNUM *b)
 {
-       int i;
-       BN_ULONG *A;
-       const BN_ULONG *B;
-
-
        if (a == b)
                return (a);
+
        if (!bn_wexpand(a, b->top))
                return (NULL);
 
-#if 1
-       A = a->d;
-       B = b->d;
-       for (i = b->top >> 2; i > 0; i--, A += 4, B += 4) {
-               BN_ULONG a0, a1, a2, a3;
-               a0 = B[0];
-               a1 = B[1];
-               a2 = B[2];
-               a3 = B[3];
-               A[0] = a0;
-               A[1] = a1;
-               A[2] = a2;
-               A[3] = a3;
-       }
-       switch (b->top & 3) {
-       case 3:
-               A[2] = B[2];
-       case 2:
-               A[1] = B[1];
-       case 1:
-               A[0] = B[0];
-       }
-#else
-       memcpy(a->d, b->d, sizeof(b->d[0]) * b->top);
-#endif
+       bn_copy_words(a->d, b->d, b->top);
 
        /* Copy constant time flag from b, but make it sticky on a. */
        a->flags |= b->flags & BN_FLG_CONSTTIME;
 
        a->top = b->top;
        a->neg = b->neg;
+
        return (a);
 }