GNU bug report logs - #47302
27.1; calc math-format-number formatting for floats without decimals is unusual

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Jelle Licht <jlicht <at> fsfe.org>
Subject: bug#47302: closed (Re: bug#47302: 27.1; calc math-format-number
 formatting for floats without decimals is unusual)
Date: Tue, 27 Apr 2021 16:16:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#47302: 27.1; calc math-format-number formatting for floats without decimals is unusual

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 47302 <at> debbugs.gnu.org.

-- 
47302: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=47302
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Dave Gillespie <Daveg <at> synaptics.com>
Cc: 47302-done <at> debbugs.gnu.org, Jelle Licht <jlicht <at> fsfe.org>,
 Stefan Kangas <stefan <at> marxist.se>
Subject: Re: bug#47302: 27.1; calc math-format-number formatting for floats
 without decimals is unusual
Date: Tue, 27 Apr 2021 18:15:43 +0200

26 apr. 2021 kl. 16.58 skrev Dave Gillespie <Daveg <at> synaptics.com>:
> 
> Yes, that patch makes sense.

Good, patch pushed as-is. It can be tweaked later on if needed. Jelle, hope this helps.

>  Thanks, and thanks for helping with this old beast!

Happy to give a hand. Nowhere else in Emacs -- and I mean this in the best possible way -- do I get a feeling of Mad Science as strongly as when dealing with Calc. "Surely Calc doesn't attempt to do this... oh yes. Yes it does."

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From: Jelle Licht <jlicht <at> fsfe.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.1; calc math-format-number formatting for floats without
 decimals is unusual
Date: Sun, 21 Mar 2021 22:54:50 +0100

[Message part 4 (text/plain, inline)]

Hey folks,

I run into the following behaviour when using calc in Emacs 27.1 (using
`emacs -Q'):

--8<---------------cut here---------------start------------->8---
(calc-eval "123.0") ; => "123."
(calc-eval "0.0") ; => "0."
--8<---------------cut here---------------end--------------->8---

I would expect this output to be either "123.0" or "123" and "0.0" or
"0" respectively.

I have attached a super simple patch that fixes this issue for me, but I
am not actually certain of the following:

- Was this formatting quirk perhaps there with a purpose? 
- Does my 'fix' have unintended consequences?

Thanks,
 Jelle

[0001-calc-Fix-formatting-of-floats-without-decimals.patch (text/x-patch, inline)]

From 88e52b073510c86b582487a65fa8ddf52a48e7dd Mon Sep 17 00:00:00 2001
From: Jelle Licht <jlicht <at> fsfe.org>
Date: Sun, 21 Mar 2021 22:39:41 +0100
Subject: [PATCH] (calc): Fix formatting of floats without decimals

* lisp/calc/calc.el (math-format-number): Fix formatting for floats
  without decimals.
---
 lisp/calc/calc.el | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lisp/calc/calc.el b/lisp/calc/calc.el
index ec09abb34c..fac9f70915 100644
--- a/lisp/calc/calc.el
+++ b/lisp/calc/calc.el
@@ -3193,8 +3193,9 @@ math-format-number
 		   ((= dpos 0)
 		    (setq str (concat "0" point str)))
 		   ((and (<= exp 0) (> dpos 0))
-		    (setq str (concat (substring str 0 dpos) point
-				      (substring str dpos))))
+                    (when (> len dpos)
+		      (setq str (concat (substring str 0 dpos) point
+				        (substring str dpos)))))
 		   ((> exp 0)
 		    (setq str (concat str (make-string exp ?0) point)))
 		   (t   ; (< dpos 0)
-- 
2.31.0

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