Re: Decimal: Formal review begins

From: Christopher Kormanyos (e_float_at_[hidden])
Date: 2025-01-20 20:59:44

 > All tests run on an i9-11900k with> Ubuntu 24.04 and the Intel(R) oneAPI> DPC++/C++ Compiler 2025.0.4> (2025.0.4.20241205). The Intel> benchmarks are written in C but> should be a faithful port. Bottom> line up front is the Intel library> is an order of magnitude faster.

> Thank you Matt. This reconciles> with what I know about everyone> using the Intel library (especially> the BSL proclamation about it> being 10 times faster). These> numbers should be added to the> documentation.
> I think there is some work to> be done to make Boost.Decimal> viable. i.e. We don't want to> be an order of magnitude slower> than what everyone else is actually> using today.
This post caused us to think andwe just kicked around a few ideas.
In the intermediate period, it wouldbe difficult to not reach the speedpublished by the Intel primitive routines.
One idea was to offer the opportunityto wrap a particular backend witha higher-level abstraction,akin to boost::multiprecision::numberwhich can wrap GMP or use our own BSLbackends. This would, however,be a new design.
We also noticed the Intel LIBsimply used float, double,long double and/or Intel's _Quadto perform elementary and specialfunctions. Fair enough, fast too.
So today we offer:  * BSL licensing  * Portability  * Boost-level testing  At the juncture of this review,I'm not sure if a 10-foldspeedup would be achievable.Maybe we would/will findab ig bottleneck in the backendintegral routines. But I feartable-lookup will always have theadvantage.
- Chris

    On Monday, January 20, 2025 at 09:28:50 PM GMT+1, Glen Fernandes via Boost <boost_at_[hidden]> wrote:  
 
 On Mon, Jan 20, 2025 at 3:11 PM Matt Borland  wrote:

> On Monday, January 20th, 2025 at 12:48 PM, Glen Fernandes  wrote:
>
> > I mentioned this to Matt, but I would like to see benchmarks comparing
> > boost::decimal64_fast to a Decimal64 backed by Intel's DFP library, which
> > is what I know to be in actual use today:
> >
> https://www.intel.com/content/www/us/en/developer/articles/tool/intel-decimal-floating-point-math-library.html
> > Not that the benchmarks comparing to GCC's Decimal64 (which is based on
> the
> > libbid which ships with libgcc) aren't useful, I personally don't know
> > anyone using that today.
> >
> > Benchmarks should ideally also include Intel's compiler, because at least
> > one of the relevant parties who motivated me to suggest the Decimal64
> > library (to Vinnie as a potential project) do use the Intel C++ compiler
> > (and their Fortran compiler) for areas where they perform better.
> >
> > (The non-fast versions don't matter to me. I don't know anyone who would
> > want to use them).
>
> Here are some preliminary results:
>
> All tests run on an i9-11900k with Ubuntu 24.04 and the Intel(R) oneAPI
> DPC++/C++ Compiler 2025.0.4 (2025.0.4.20241205). The Intel benchmarks are
> written in C but should be a faithful port. Bottom line up front is the
> Intel library is an order of magnitude faster.
>

Thank you Matt.  This reconciles with what I know about everyone using the
Intel library (especially the BSL proclamation about it being 10 times
faster). These numbers should be added to the documentation.

I think there is some work to be done to make Boost.Decimal viable. i.e. We
don't want to be an order of magnitude slower than what everyone else is
actually using today.

Glen

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