[Vm-dev] Re: [squeak-dev] New Cog VMs available

[Luciano Notarfrancesco]

Hi Eliot,
My only point is performance. GMP is highly optimized, it includes
optimizations made by hand for each particular processor, so for example
the multiplication of large enough integers should be much faster than our
implementation in Slang. And it seems that we wouldn't need to change
anything in the image or do any conversions or marshaling, just call the
mpn_* low-level functions from the large integers plugin. But if we have to
marshal everything it doesn't make much sense to use GMP, because it will
be slower for relatively small large integers.

I'm working on computer algebra in Smalltalk and I'd like to be competitive
with other computer algebra systems (GAP, Magma, etc), and in many cases
the bottleneck is large integer arithmetic.

So I'm very happy about the recent speed up using 32 bits legs and avoiding
function calls for type checking. That will have an impact in my
benchmarks. Thanks!


On Wed, Jul 13, 2016 at 12:52 PM, Eliot Miranda <eliot.miranda at gmail.com>
wrote:

> 1. the existing code is functional and adequate.  GMP offers no new
> functionality and may offer performance improvements or may not.  But the
> existing code is capable of being tuned also.
>
> 2. The existing plugin is internal; with the "new" linkage I wrote two
> years ago now internal plugins have a much simpler call interface into the
> VM (no double calls through a pointer anymore; just direct calls on the VM
> functions). But LGPL forces us to make the plugin external.  Hence using
> GMP implies a loss of performance in marshaling arguments and allocating
> and returning results.
>
> IMO these two together make GMP irrelevant.  Less compelling reasons are
>
> 3. Yet another library to install on all build environments; AFAIA it's
> not present on non-Linux platforms
>
> 4. Being a library we don't control we're dependent on others fixing it.
>
> What reasons, other than brand identity are there for using GMP?
>
> Could we use it if was already installed in the host platform? It seems to
> me that it would be quite straight forward to call to the GMP low-level API
> from the LargeIntegersPlugin, without making any changes in the image.
> https://gmplib.org/manual/Low_002dlevel-Functions.html
>
>
>
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