From: Helmut Eller <eller.helmut@gmail.com>
To: emacs-devel@gnu.org
Subject: Re: integer overflow handling for most-negative-fixnum
Date: Sat, 21 Jul 2018 14:42:20 +0200 [thread overview]
Message-ID: <m2o9f0lpzn.fsf@gmail.com> (raw)
In-Reply-To: 866018yl76.fsf@gmail.com
> Either the print routines or the reader have a bug.
Read and print work just fine:
(= (read (prin1-to-string most-negative-fixnum))
most-negative-fixnum) => t
The problem is (format "%x" most-negative-fixnum) => "2000000000000000".
If this should return "-1" that would obviously be an incompatible
change. And in many cases one really wants to "see" the two complement
representation of negative fixnums. Just like in gdb: p/x -1 prints
0xffffff. Interestingly, gdb doesn't seem to have a mode to print hex
numbers with a negative sign; so I guess nobody ever wanted that.
In contrast, it should be unproblematic to add an optional base argument
to number-to-string. So (number-to-string -1 16) could return
"-2000000000000000" without breaking anything. Actually, I occasionally
wondered why string-to-number accepts a base argument but
number-to-string doesn't.
(Of course, the question what (format "%x" <bignum>) should do is still
open; the easiest would probably be to signal an error.)
Helmut
next prev parent reply other threads:[~2018-07-21 12:42 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
2018-07-21 18:51 ` Eli Zaretskii
2018-07-21 20:42 ` Stefan Monnier
2018-07-21 12:42 ` Helmut Eller [this message]
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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