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: Mattias Engdegård <mattiase <at> acm.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#47302: closed (27.1; calc math-format-number formatting for
 floats without decimals is unusual)
Date: Tue, 27 Apr 2021 16:16:02 +0000

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Your message dated Tue, 27 Apr 2021 18:15:43 +0200
with message-id <58E10359-2CE0-4BF8-936E-47E5DCDA77E4 <at> acm.org>
and subject line Re: bug#47302: 27.1; calc math-format-number formatting for floats without decimals is unusual
has caused the debbugs.gnu.org bug report #47302,
regarding 27.1; calc math-format-number formatting for floats without decimals is unusual
to be marked as done.

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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

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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

[Message part 5 (message/rfc822, inline)]

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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