From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: Toru TSUNEYOSHI <t_tuneyosi@hotmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?
Date: Fri, 23 Oct 2009 17:14:26 -0400 [thread overview]
Message-ID: <jwvvdi57r5c.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <BLU0-SMTP78C64056174E8A0EBF01DCE2BD0@phx.gbl> (Toru TSUNEYOSHI's message of "Sat, 24 Oct 2009 02:51:47 +0900")
> I read the code of function `string-to-number', and traced functions or
> macros recursively.
> traces of string-to-number:
> data.c: Fstring_to_number
> lisp.h: make_fixnum_or_float
> lisp.h: FIXNUM_OVERFLOW_P
> citation of FIXNUM_OVERFLOW_P (in Emacs 23.1):
> /* Value is non-zero if C integer I doesn't fit into a Lisp fixnum. */
> #define FIXNUM_OVERFLOW_P(i) \
> ((EMACS_INT)(i) > MOST_POSITIVE_FIXNUM \
> || (EMACS_INT) (i) < MOST_NEGATIVE_FIXNUM)
> I think FIXNUM_OVERFLOW_P is problematic.
> The reason is that
> in case `i' is 4294967296.0 (2^32), (EMACS_INT)(i) returns 0
> with a executable program by some compiler
> (for example, Microsoft 32-bit C/C++ Compiler).
> As a result, FIXNUM_OVERFLOW_P(i) returns 0.
> In Microsoft 32-bit C/C++ Compiler:
> i (int)(i)
> ===============================================
> 2147483648.0 (2^31) -2147483648
> 2147483647.0 (2^31 - 1) 2147483647
> 4294967296.0 (2^32) 0
> 4294967295.0 (2^32 - 1) -1
> 8589934592.0 (2^33) 0
> 8589934591.0 (2^33 - 1) -1
> In gcc version 3.4.4 (cygming special):
> i (int)(i)
> ===============================================
> 2147483648.0 (2^31) -2147483648
> 2147483647.0 (2^31 - 1) 2147483647
> 4294967296.0 (2^32) -2147483648
> 4294967295.0 (2^32 - 1) -2147483648
> 8589934592.0 (2^33) -2147483648
> 8589934591.0 (2^33 - 1) -2147483648
> In conclusion, it needs casting to double, I think.
> #define FIXNUM_OVERFLOW_P(i) \
> ((double)(i) > (double)MOST_POSITIVE_FIXNUM \
> || (double)(i) < (double)MOST_NEGATIVE_FIXNUM)
> What do you think about it ?
I think the problem is that FIXNUM_OVERFLOW_P is written to handle an
integer argument, not a float argument. So rather than patch it to use
floats, I'd rather write a new macro that works for floats (and only
casts the MOST_POSITIVE_FIXNUM side).
Stefan
next prev parent reply other threads:[~2009-10-23 21:14 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-23 17:51 macro FIXNUM_OVERFLOW_P in lisp.h is valid ? Toru TSUNEYOSHI
2009-10-23 19:33 ` Eli Zaretskii
2009-10-24 1:50 ` Toru TSUNEYOSHI
2009-10-24 9:05 ` Eli Zaretskii
2009-10-24 11:59 ` Toru TSUNEYOSHI
2009-10-24 13:00 ` Eli Zaretskii
2009-10-24 18:45 ` Toru TSUNEYOSHI
2009-10-24 15:14 ` Andreas Schwab
2009-10-24 18:39 ` Stefan Monnier
2009-10-26 14:48 ` Toru TSUNEYOSHI
[not found] ` <20091024.105033.100383844.t_tuneyosi@hotmail.com>
2009-10-24 6:07 ` Toru TSUNEYOSHI
[not found] ` <20091024.150744.186061320.t_tuneyosi@hotmail.com>
2009-10-24 7:46 ` Toru TSUNEYOSHI
2009-10-24 10:11 ` Eli Zaretskii
2009-10-23 20:57 ` Andreas Schwab
2009-10-23 22:02 ` Eli Zaretskii
2009-10-24 1:05 ` Stefan Monnier
2009-10-24 9:15 ` Eli Zaretskii
2009-10-24 9:40 ` Andreas Schwab
2009-10-24 10:16 ` Eli Zaretskii
2009-10-24 10:01 ` Andreas Schwab
2009-10-23 21:14 ` Stefan Monnier [this message]
2009-10-25 8:51 ` Toru TSUNEYOSHI
[not found] ` <20091025.175131.55657724.t_tuneyosi@hotmail.com>
2009-10-25 11:30 ` Toru TSUNEYOSHI
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=jwvvdi57r5c.fsf-monnier+emacs@gnu.org \
--to=monnier@iro.umontreal.ca \
--cc=emacs-devel@gnu.org \
--cc=t_tuneyosi@hotmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).