GNU bug report logs - #17681
24.3.91; "Arithmetic Error" in hide-ifdef mode when using shift operators

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: David Engster <deng <at> randomsample.de>
Subject: bug#17681: closed (Re: bug#17681: 24.3.91; "Arithmetic Error" in
 hide-ifdef mode when using shift operators)
Date: Sun, 26 Jun 2016 04:54:02 +0000

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Your bug report

#17681: 24.3.91; "Arithmetic Error" in hide-ifdef mode when using shift operators

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 17681 <at> debbugs.gnu.org.

-- 
17681: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17681
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Noam Postavsky <npostavs <at> users.sourceforge.net>
To: 17681-done <at> debbugs.gnu.org
Subject: Re: bug#17681: 24.3.91; "Arithmetic Error" in hide-ifdef mode when
 using shift operators
Date: Sun, 26 Jun 2016 00:53:39 -0400

Version: 25.0.95

I see the problem in Emacs 24.5, but not Emacs 25.0.95, so it seems to
have been fixed sometime in between.

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From: David Engster <deng <at> randomsample.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.91;
 "Arithmetic Error" in hide-ifdef mode when using shift operators
Date: Tue, 03 Jun 2014 21:12:33 +0200

Recipe:

- Create a file "test.h" containing the following (this is from
  the file 'jiffies.h' in the Linux kernel):

#if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
#endif

- emacs -Q

- Load the file, activate hide-ifdef-mode

- C-c @ h  (hide-ifdefs)

The minibuffer will show "Arithmetic Error". Here is the backtrace:

Debugger entered--Lisp error: (arith-error)
  hif-divide(0 nil)
  (hif-shiftleft (hif-divide (hif-shiftleft (hif-lookup (quote NSEC_PER_SEC)) 2) (hif-lookup (quote TICK_NSEC))) (hif-minus (hif-lookup (quote SEC_JIFFIE_SC)) 2))
  (hif-logand (hif-shiftleft (hif-divide (hif-shiftleft (hif-lookup (quote NSEC_PER_SEC)) 2) (hif-lookup (quote TICK_NSEC))) (hif-minus (hif-lookup (quote SEC_JIFFIE_SC)) 2)) 2147483648.0)
  (hif-not (hif-logand (hif-shiftleft (hif-divide (hif-shiftleft (hif-lookup (quote NSEC_PER_SEC)) 2) (hif-lookup (quote TICK_NSEC))) (hif-minus (hif-lookup (quote SEC_JIFFIE_SC)) 2)) 2147483648.0))
  eval((hif-not (hif-logand (hif-shiftleft (hif-divide (hif-shiftleft (hif-lookup (quote NSEC_PER_SEC)) 2) (hif-lookup (quote TICK_NSEC))) (hif-minus (hif-lookup (quote SEC_JIFFIE_SC)) 2)) 2147483648.0)))
  hif-possibly-hide()
  hide-ifdef-guts()
  hide-ifdefs()

Earlier Emacsen did not throw an error here (although it is very
possible that the above line wasn't calculated correctly). Still, this
probably qualifies as a regression.

-David

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