From: Andy Polyakov <appro@openssl.org>
Date: Mon, 14 Nov 2011 21:14:53 +0000 (+0000)
Subject: ec_cvt.c: performance update from HEAD.
X-Git-Tag: OpenSSL_1_0_1-beta1~73
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=17674bfdf75bffa4e225f8328b9d42cb74504005;p=oweals%2Fopenssl.git

ec_cvt.c: performance update from HEAD.
---

diff --git a/crypto/ec/ec_cvt.c b/crypto/ec/ec_cvt.c
index bbed1da455..bfcbab35fe 100644
--- a/crypto/ec/ec_cvt.c
+++ b/crypto/ec/ec_cvt.c
@@ -78,7 +78,32 @@ EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a, const BIGNUM
 	const EC_METHOD *meth;
 	EC_GROUP *ret;
 
+#if defined(OPENSSL_BN_ASM_MONT)
+	/*
+	 * This might appear controversial, but the fact is that generic
+	 * prime method was observed to deliver better performance even
+	 * for NIST primes on a range of platforms, e.g.: 60%-15%
+	 * improvement on IA-64, ~25% on ARM, 30%-90% on P4, 20%-25%
+	 * in 32-bit build and 35%--12% in 64-bit build on Core2...
+	 * Coefficients are relative to optimized bn_nist.c for most
+	 * intensive ECDSA verify and ECDH operations for 192- and 521-
+	 * bit keys respectively. Choice of these boundary values is
+	 * arguable, because the dependency of improvement coefficient
+	 * from key length is not a "monotone" curve. For example while
+	 * 571-bit result is 23% on ARM, 384-bit one is -1%. But it's
+	 * generally faster, sometimes "respectfully" faster, sometimes
+	 * "tolerably" slower... What effectively happens is that loop
+	 * with bn_mul_add_words is put against bn_mul_mont, and the
+	 * latter "wins" on short vectors. Correct solution should be
+	 * implementing dedicated NxN multiplication subroutines for
+	 * small N. But till it materializes, let's stick to generic
+	 * prime method...
+	 *						<appro>
+	 */
+	meth = EC_GFp_mont_method();
+#else
 	meth = EC_GFp_nist_method();
+#endif
 	
 	ret = EC_GROUP_new(meth);
 	if (ret == NULL)