From: Andy Moreton <andrewjmoreton@gmail.com>
To: 32463@debbugs.gnu.org
Subject: bug#32463: 27.0.50; (logior -1) => 4611686018427387903
Date: Fri, 17 Aug 2018 14:24:02 +0100 [thread overview]
Message-ID: <vz1o9e15dot.fsf@gmail.com> (raw)
In-Reply-To: <b4m8t55llg6.fsf@jpl.org>
On Fri 17 Aug 2018, Pip Cet wrote:
> On Fri, Aug 17, 2018 at 9:34 AM Andy Moreton <andrewjmoreton@gmail.com> wrote:
> Paul committed a patch in the meantime (independently, I think?) which
> does add tests. I'll try to write some more.
Thanks. I should have done that with my patches to fix some bignum bugs.
>> The tdiv/fdiv were
>> added to give expected results. Pay particular attention to values around
>> most-positive-fixnum and most-negative-fixnum.
>
> I don't think they do give the expected results. We should discuss
> that in more detail, but first, can we agree that lsh and ash behave
> the same for bignums? If so, clearly one branch of the code you quoted
> is incorrect, and I think it's the tdiv one.
I agree that for bignums lsh and ash should behave the same way. I can
easily belive that there are bugs in this code, as I was fighting
problems with 64bit Windows having 32bit long at the same time.
> I ran:
>
> (require 'cl)
>
> (let ((i 0))
> (while (< i 128)
> (message "%d %x" i (lsh (- (lsh -1 i) 1) -1))
> (incf i)))
Or equivalently:
(dotimes (i 128) (message "%d %x" i (lsh (1- (lsh -1 i)) -1)))
> and got this output:
>
> [...]
> 57 -100000000000001
> 58 -200000000000001
> 59 -400000000000001
> 60 -800000000000001
> 61 -1000000000000000
> 62 -2000000000000000
> 63 -4000000000000000
> 64 -8000000000000000
> [...]
>
> Something is wrong there.
Yes, this is clearly not behaving correctly and needs to be fixed.
Thanks for investigating this.
AndyM
next prev parent reply other threads:[~2018-08-17 13:24 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-17 3:29 bug#32463: 27.0.50; (logior -1) => 4611686018427387903 Katsumi Yamaoka
2018-08-17 5:59 ` Pip Cet
2018-08-17 7:40 ` Katsumi Yamaoka
2018-08-17 9:27 ` Andy Moreton
2018-08-17 11:36 ` Pip Cet
2018-08-17 11:53 ` Pip Cet
2018-08-17 13:27 ` Andy Moreton
2018-08-18 22:43 ` Paul Eggert
2018-08-17 13:24 ` Andy Moreton [this message]
2018-08-18 18:48 ` Paul Eggert
2018-08-18 18:59 ` Eli Zaretskii
2018-08-18 19:58 ` Pip Cet
2018-08-18 22:27 ` Paul Eggert
2018-08-19 15:03 ` Eli Zaretskii
2018-08-18 19:59 ` Paul Eggert
2018-08-18 19:45 ` Andy Moreton
2018-08-19 10:43 ` Live System User
2018-08-20 3:02 ` Richard Stallman
2018-08-20 3:47 ` Paul Eggert
2018-08-21 3:37 ` Richard Stallman
2018-08-18 22:56 ` Paul Eggert
2018-08-18 23:17 ` Paul Eggert
2018-08-19 10:34 ` Andy Moreton
2018-08-19 10:48 ` Pip Cet
2018-08-19 10:59 ` Paul Eggert
2018-08-19 11:32 ` Pip Cet
2018-08-21 9:40 ` Paul Eggert
2018-08-21 10:50 ` Andy Moreton
2018-08-21 14:36 ` Eli Zaretskii
2018-08-21 14:52 ` Andy Moreton
2018-08-21 17:24 ` Paul Eggert
2018-08-19 10:52 ` Paul Eggert
2018-08-22 2:29 ` Paul Eggert
2018-08-22 16:56 ` Tom Tromey
2018-08-22 17:52 ` Paul Eggert
2018-08-22 18:25 ` Eli Zaretskii
2018-08-23 0:28 ` Paul Eggert
2018-08-23 2:39 ` Eli Zaretskii
2018-08-19 18:00 ` Andy Moreton
2018-08-22 2:34 ` Paul Eggert
2018-08-22 23:27 ` Andy Moreton
2018-08-23 14:05 ` Eli Zaretskii
2018-08-22 2:56 ` Paul Eggert
2018-08-22 8:20 ` Andy Moreton
2018-08-22 8:39 ` Andy Moreton
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