From d8ea368c41ae6716af6b48f55f9b888a32c37e06 Mon Sep 17 00:00:00 2001 From: Andy Polyakov Date: Sat, 21 May 2011 08:40:18 +0000 Subject: [PATCH] ec_cvt.c: ARM comparison results were wrong, clarify the background. --- crypto/ec/ec_cvt.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/crypto/ec/ec_cvt.c b/crypto/ec/ec_cvt.c index a99d762d3b..dffd70521a 100644 --- a/crypto/ec/ec_cvt.c +++ b/crypto/ec/ec_cvt.c @@ -85,15 +85,21 @@ EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a, const BIGNUM * 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, 50%-20% on ARM, 30%-90% on P4, 20%-25% + * 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. What effectively happens is that loop - * with bn_mul_add_words is put against bn_mul_mont, and 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... + * 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, or + * "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... * */ meth = EC_GFp_mont_method(); -- 2.25.1