ec_cvt.c: ARM comparison results were wrong, clarify the background.

	 * 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...

	 *						<appro>

	 */

	meth = EC_GFp_mont_method();