GNU bug report logs - #43764
Calc shift right broken

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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#43764: closed (Calc shift right broken)
Date: Tue, 13 Oct 2020 09:58:02 +0000

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Your message dated Tue, 13 Oct 2020 11:56:50 +0200
with message-id <550C4DEF-DBAA-4175-98BC-DB484A3B89CF <at> acm.org>
and subject line Re: bug#43764: Calc shift right broken
has caused the debbugs.gnu.org bug report #43764,
regarding Calc shift right broken
to be marked as done.

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help-debbugs <at> gnu.org.)


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From: Vincent Belaïche <vincent.b.1 <at> hotmail.fr>
To: "bug-gnu-emacs <at> gnu.org" <bug-gnu-emacs <at> gnu.org>
Subject: Calc shift right broken
Date: Fri, 2 Oct 2020 15:28:22 +0000

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Not sure whether this has to do with the other one.
I am on another machine, it is GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20) of 2020-05-17, modified by Debian

Anyway, I do this:

2 RET
;; display in hexa
d 6 RET
;; Raise to the power 32
32 ^
;; Shitf right by 30
C-u 32 b r
;; I get 0, whereas I expected 4

I have the impression that the old bigpos bigneg lisp based big intergers have been replaced by C bigintegers, and this is the root of all these regression.
Well, just a speculation.
  V.

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Vincent Belaïche <vincent.b.1 <at> hotmail.fr>
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>, 43764-done <at> debbugs.gnu.org
Subject: Re: bug#43764: Calc shift right broken
Date: Tue, 13 Oct 2020 11:56:50 +0200

9 okt. 2020 kl. 17.34 skrev Vincent Belaïche <vincent.b.1 <at> hotmail.fr>:

> 	• set bit width 0 would remove the automatic clipping meaning infinite width.

The previously mentioned patch implementing this has now been pushed to Emacs master. Thanks again for the suggestion!

I should also note the rationale for disabling left/right rotation when the word size is set to zero: while it would make sense to define

 (rotate-left x 1) =>
 x≥0: (shift-left x 1)
 x<0: (+ (shift-left x 1) 1)

 (rotate-right x 1) =>
 x≥0, x even: (shift-right x 1)
 x<0, x odd:  (shift-right x 1),

the two remaining cases of rotate right with {x≥0, x odd} or {x<0, x even} cannot result in a finite integer.

If someone has a better idea, or would like rotation to be implemented as a partial function according to the above definition, please comment. For now the bug is closed.

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