From: Paul Eggert <eggert@cs.ucla.edu>
To: Andy Moreton <andrewjmoreton@gmail.com>, emacs-devel@gnu.org
Subject: Re: integer overflow handling for most-negative-fixnum
Date: Fri, 20 Jul 2018 15:10:07 -0700 [thread overview]
Message-ID: <b713841d-ad3d-bf68-049a-7ae31f9297ee@cs.ucla.edu> (raw)
In-Reply-To: <867elsq78b.fsf@gmail.com>
On 07/18/2018 07:39 PM, Andy Moreton wrote:
>> + (should-error (read (format "#x%x" most-negative-fixnum))
>> + :type 'overflow-error)
>> + (should-error (read (format "#o%o" most-negative-fixnum))
>> + :type 'overflow-error)
> However, these tests (and the overflow behaviour) seem completely wrong
> to me. The reported error is for an out of range fixnum, when what was
> tested was an explicitly valid integer value.
Here, the code is executing something like (read "#x2000000000000000"),
which is indeed out of range for a fixnum, since fixnums are signed and
go up only to #x1fffffffffffffff (on 64-bit hosts).
> Why are non-base10 numbers treated as signed ?
Emacs fixnums are signed; there is no 'unsigned' type in Emacs Lisp.
Although we could of course add such a type, it'd be better to expend
our limited development resources on adding bignums. The 'unsigned' type
in C has been a glitch magnet.
It might perhaps be useful to add an Emacs Lisp syntax for negative
hexadecimal numbers, e.g., -#x10 would be equivalent to -16.
> Why does the error message ignore the base of the input value ? It
> should give a more accurate description of the problematic input.
Yes, it should. I'll see if I can pry loose some time to look into that.
next prev parent reply other threads:[~2018-07-20 22:10 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 [this message]
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
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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