bn/bn_exp.c: prefer MULX/AD*X over AVX2.

37de2b5c · Andy Polyakov · 2d752737 · 37de2b5c
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crypto/bn/bn_exp.c crypto/bn/bn_exp.c +2 -1

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--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -691,7 +691,8 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
 	 * RSAZ exponentiation. For further information see
 	 * crypto/bn/rsaz_exp.c and accompanying assembly modules.
 	 */
-	if ((16 == a->top) && (16 == p->top) && (BN_num_bits(m) == 1024)
+	if (((OPENSSL_ia32cap_P[2]&0x80100) != 0x80100) /* check for MULX/AD*X */
+	    && (16 == a->top) && (16 == p->top) && (BN_num_bits(m) == 1024)
 	    && rsaz_avx2_eligible())
 	    	{
 		if (NULL == bn_wexpand(rr, 16)) goto err;