Thread: AVX-ECM
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Old 2020-11-29, 18:13   #76
bsquared's Avatar
Feb 2007

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Originally Posted by Prime95 View Post
Have you played with improving PRAC?

I recently did and gained one or two percent. This may be because prime95 can store data FFTed which may change the costing functions. A double costs 10 transforms, an add costs 12 transforms. Also, prime95 is usually dealing with larger numbers and can afford to spend a little more time searching for the best chain.

Glad to share the C code for the changes.
I tried to adjust the balance of time optimizing chains, without notable success. I'd like to see your code, thanks for sharing.

I'm also looking into gmp-ecm's different parameterizations. "param 1" seems to be the default for me in most cases. It looks like they are using small parameters so that the multiply by (A+2)/4 is a single limb (saving a multiply when duplicating). Then not using PRAC at all, instead using Montgomery's ladder, which has a larger percentage of doublings, on a pre-multiplied set of B1 primes. Eliminating a multiply could save 10% or so. What I don't understand yet is how it can be single-limb if they are using montgomery multiplies (redc).

Last fiddled with by bsquared on 2020-11-29 at 18:16
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