From: Eli Zaretskii <eliz@gnu.org>
To: Toru TSUNEYOSHI <t_tuneyosi@hotmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?
Date: Sat, 24 Oct 2009 15:00:03 +0200 [thread overview]
Message-ID: <83my3heylo.fsf@gnu.org> (raw)
In-Reply-To: <BLU0-SMTP851948576B95B32672B229E2BC0@phx.gbl>
> Date: Sat, 24 Oct 2009 20:59:47 +0900
> Cc: emacs-devel@gnu.org
> From: Toru TSUNEYOSHI <t_tuneyosi@hotmail.com>
>
> BTW, how does Emacs on 64-bit platforms eval the following expressions?
>
> (string-to-number "1152921504606846975") ; 2^60 - 1
> => 1.1529215046068467e+018 ; on 32-bit platforms
>
> On 64-bit platforms, string-to-number should return the number as type
> `EMACS_INT' (= `LONG'), I think.
Yes, it should.
> Although, the code of string-to-number (Fstring_to_number) deals with
> the number as type `double' (of variable `v').
Yes, it does. And thus it loses least significant digits:
(string-to-number "1152921504606846975") => 1152921504606846720
> #define make_fixnum_or_float(val) \
> (FIXNUM_OVERFLOW_P (val) \
> ? make_float (val) \
> : make_number ((EMACS_INT)(val)))
>
> In this code, FIXNUM_OVERFLOW_P (val) will returns 0.
> Then Emacs processes `make_number ((EMACS_INT)(val)))'.
> On that time, `val' is casted from type `double' to `EMACS_INT'.
> At last, can string-to-number return all digits of the number
> 1152921504606846975 properly?
>
> I guessed it can't.
> That is the reason why I made my former patch.
OK, but please make your patch compare against MOST_POSITIVE_FIXNUM,
instead of using INT_MAX or LONG_MAX. Also, if you know that the
value does not overflow an EMACS_INT, you can simply call make_number,
instead of make_fixnum_or_float.
next prev parent reply other threads:[~2009-10-24 13:00 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 [this message]
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
2009-10-25 8:51 ` Toru TSUNEYOSHI
[not found] ` <20091025.175131.55657724.t_tuneyosi@hotmail.com>
2009-10-25 11:30 ` Toru TSUNEYOSHI
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