From: Steffen Nurpmeso <steffen@sdaoden.eu>
Subject: Re: exact floating point calculations in roff(7)
To: Ingo Schwarze <schwarze@usta.de>
Cc: j@bitminer.ca, tech@openbsd.org
Date: Sat, 05 Apr 2025 22:22:35 +0200

Ingo Schwarze wrote in
 <Z-56l-go74Cf70fQ@isnote.usta.de>:
 ...
 |Before i wrote the double arithmetic code, that code did use integer
 |arithmetic.  I had written that integer arithmetic code several years
 |earlier.
 |
 |> decided, instead, to adopt doubles.
 |
 |I deemed the change necessary because the roff(7) input syntax
 |supports decimal fractions.
 |
 |Admittedly, it might be possible to parse 23.999 as *two* integers
 |(23 and 999), scale both parts separately, do some kind of carry,
 |and finally add both results, all using integer arithmetics.
 |I admit i did not consider that possibility when switching this
 |code to floating point, but it does not feel like a simple solution.

I mean, you *could* also ask "which is the largest output size
i want to support" on the one hand, and on the other count
fraction digits.  Ie, always work with "super-scaled" 64-bit
integer arithmetic.  Just wanted to add that.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)