The efforts to eliminate the dual-representation of zero and to ensure

bignums are passed in and out of functions and APIs in a consistent form
has highlighted that zero-valued bignums don't need any allocated word
data. The use of BN_set_word() to initialise a bignum to zero causes
needless allocation and gives it a return value that must be checked. This
change converts BN_zero() to a self-contained macro that has no
return/expression value and does not cause any expansion of bignum data.

Note, it would be tempting to rewrite the deprecated version as a
success-valued comma expression, such as;
   #define BN_zero(a) ((a)->top = (a)->neg = 0, 1)
However, this evaluates 'a' twice and would confuse initialisation loops
(eg. while(..) { BN_zero(bn++) } ). As such, the deprecated version
continues to use BN_set_word().

diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index f58d5f55a07bd58420ce6d63bf5254b317e4f6c3..a01f193daaf212b8b16333280e2f465eb73032ec 100644 (file)
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -372,7 +372,17 @@ int BN_GENCB_call(BN_GENCB *cb, int a, int b);
 #define BN_is_odd(a)       (((a)->top > 0) && ((a)->d[0] & 1))
 
 #define BN_one(a)      (BN_set_word((a),1))
+#define BN_zero_ex(a) \
+       do { \
+               BIGNUM *_tmp_bn = (a); \
+               _tmp_bn->top = 0; \
+               _tmp_bn->neg = 0; \
+       } while(0)
+#ifdef OPENSSL_NO_DEPRECATED
+#define BN_zero(a)     BN_zero_ex(a)
+#else
 #define BN_zero(a)     (BN_set_word((a),0))
+#endif
 /* BN_set_sign(BIGNUM *, int) sets the sign of a BIGNUM
  * (0 for a non-negative value, 1 for negative) */
 #define BN_set_sign(a,b) ((a)->neg = (b))