Re: Decimal: Formal review begins.

From: Matt Borland (matt_at_[hidden])
Date: 2025-01-20 17:57:28

On Monday, January 20th, 2025 at 11:52 AM, Klemens Morgenstern via Boost <boost_at_[hidden]> wrote:

> 

> 

> On Wed, Jan 15, 2025 at 5:34 PM John Maddock via Boost <
> boost_at_[hidden]> wrote:
> 

> > The review of the proposed Decimal Number library by Matt Borland and
> > Chris Kormanyos begins today and runs until 22nd Jan.
> > 

> > You will find documentation here:
> > https://cppalliance.org/decimal/decimal.html
> > 

> > And the code repository is here: https://github.com/cppalliance/decimal/
> > 

> > Boost.Decimal is an implementation of IEEE 754
> > https://standards.ieee.org/ieee/754/6210/ and ISO/IEC DTR 24733
> > https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2009/n2849.pdf
> > Decimal Floating Point numbers. The library is header-only, has no
> > dependencies, and requires C++14.
> 

> 

> Thanks to Matt & Chris for submitting your library for review. From
> glancing at the docs it looks great. However, I got a very basic question:
> 

> What are the actual applications for decimal floating points? Where are
> they used or where would potential users want to use them?
> 

The canonical example is finance. We have an example[1] where a user can parse a CSV of stock pricing data without the rounding error that would come with binary floating point, and then are able to perform analysis leveraging Boost.Math.   

> Why wouldn't one just use fixed-point arithmetic when the binary floating
> points don't provide the proper rounding behaviour?
> 

In one of Reuben's questions he asked about emulating fixed-point and I believe that is possible, but have not tried to do it myself. We have a user who was using fixed-point arithmetic, but when they needed to support bitcoins it exceeded the precision of their fixed-point system so they either had to re-write or use an off the shelf solution like we offer here. They chose the latter and to my knowledge it has worked out for them.

Matt

[1] https://github.com/cppalliance/decimal/blob/develop/examples/statistics.cpp