From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: integer overflow handling for most-negative-fixnum
Date: Sat, 21 Jul 2018 14:42:32 -0400 [thread overview]
Message-ID: <jwv7elophkk.fsf-monnier+Inbox@gnu.org> (raw)
In-Reply-To: <83d0vgxxx8.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 21 Jul 2018 21:10:11 +0300")
>> Not sure what "fix the reader" would do here. Do you mean read
>> #x2000000000000000 as a negative number?
> Yes. More importantly, I'd like it to read #x3fffffffffffffff as -1.
Hmm... me don't like that at all.
>> When/why/where would that be a good idea?
> When wouldn't it be a good idea?
When the user wrote #x3fffffffffffffff to mean "the positive number
written as 3fffffffffffffff in hexadecimal" (which as far as I know is
what "#x3fffffffffffffff" means in Elisp).
You can only read it as "-1" based on an assumption of fixed-width
two's-complement representation but the bitwidth of Emacs numbers is
something that can change between Emacs versions and
compilation options. [ Especially since the leading digit is "3"
rather than "f", which means it can only be treated as -1 under the
assumption that the author really knew *exactly* how many bits his
particular Emacs build uses for integers. ]
Stefan
next prev parent reply other threads:[~2018-07-21 18:42 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-19 2:39 integer overflow handling for most-negative-fixnum Andy Moreton
2018-07-20 22:10 ` Paul Eggert
2018-07-21 5:22 ` Helmut Eller
2018-07-21 9:47 ` Andy Moreton
2018-07-21 10:14 ` Eli Zaretskii
2018-07-21 13:06 ` Andy Moreton
2018-07-21 17:15 ` Stefan Monnier
2018-07-21 17:48 ` Paul Eggert
2018-07-21 18:12 ` Stefan Monnier
2018-07-23 19:18 ` Paul Eggert
2018-07-23 19:57 ` Stefan Monnier
2018-07-23 23:09 ` Paul Eggert
2018-07-21 20:10 ` Helmut Eller
2018-07-21 21:02 ` Helmut Eller
2018-07-23 19:40 ` Paul Eggert
2018-07-21 18:10 ` Eli Zaretskii
2018-07-21 18:17 ` Paul Eggert
2018-07-21 18:23 ` Eli Zaretskii
2018-07-21 18:42 ` Stefan Monnier [this message]
2018-07-21 18:51 ` Eli Zaretskii
2018-07-21 20:42 ` Stefan Monnier
2018-07-21 12:42 ` Helmut Eller
2018-07-21 17:46 ` Paul Eggert
2018-07-23 11:49 ` Andy Moreton
2018-07-23 17:30 ` Paul Eggert
2018-07-23 21:11 ` Andy Moreton
2018-07-24 12:14 ` Andreas Schwab
2018-07-24 13:06 ` Andy Moreton
2018-07-21 9:49 ` Paul Eggert
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