From: Eric Wong <normalperson@...>
Date: 2013-08-16T19:32:20+00:00
Subject: [ruby-core:56659] Re: [ruby-trunk - Feature #8796][Open] Use GMP to accelerate Bignum operations

"akr (Akira Tanaka)" <akr@fsij.org> wrote:
> If a user don't want to use GMP, a configure option, --without-gmp,
> disables this feature.
> Since GMP is licensed as LGPL, some people would need it.
> However I think most people can accept LGPL as Ruby 1.8's regex engine.
> So, my patch uses GMP by default, if it is available.

I'm happy with LGPL :)

> It converts bignums from RBignum to mpz_t and back for each
> large Bignum multiplication.
> RBignum structure itself is not changed and ABI compatible.
> (So, this is different from ko1's idea mentioned in Feature #6083)
> 
> The conversion cost is O(n).
> It is negligible for operations slower than O(n) with large inputs.
> Multiplication is a kind of such operation.

Is there more performance improvement without the conversion?

How about push the conversion cost to legacy C API users to make
Bignum faster for pure-Ruby use in a future patch?

I'm mainly curious about "smaller" Bignums for users on 32-bit systems,
but I suspect much of that cost is object allocation.