Re: Decimal: Formal review begins

From: Matt Borland (matt_at_[hidden])
Date: 2025-01-20 20:11:43

On Monday, January 20th, 2025 at 12:48 PM, Glen Fernandes via Boost <boost_at_[hidden]> 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).
> 

> Glen

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.

Intel

===== Comparisons =====
Comparisons    <Decimal32  >: 73831      us
Comparisons    <Decimal64  >: 76725      us

===== Addition =====
Addition       <Decimal32  >: 81544      us
Addition       <Decimal64  >: 86667      us

===== Subtraction =====
Subtraction    <Decimal32  >: 81736      us
Subtraction    <Decimal64  >: 86587      us

===== Multiplication =====
Multiplication <Decimal32  >: 81631      us
Multiplication <Decimal64  >: 86939      us

Proposal and built-in types

===== Comparisons =====
comparisons<float      >: 73013      us
comparisons<double     >: 104019     us
comparisons<dec32_fast >: 562165     us
comparisons<dec64_fast >: 592997     us

===== Addition =====
Addition<float      >: 78622      us
Addition<double     >: 74393      us
Addition<dec32_fast >: 1164565    us
Addition<dec64_fast >: 1045147    us

===== Subtraction =====
Subtraction<float      >: 78787      us
Subtraction<double     >: 73223      us
Subtraction<dec32_fast >: 1076833    us
Subtraction<dec64_fast >: 920855     us

===== Multiplication =====
Multiplication<float      >: 78457      us
Multiplication<double     >: 74345      us
Multiplication<dec32_fast >: 1208233    us
Multiplication<dec64_fast >: 803870     us

This paper was linked in their readme: https://www.lirmm.fr/arith18/papers/CorneaM_Decimal_ARITH18.pdf. Their advantage seems to stem from leveraging lookup tables extensively.

Matt