From: Dmitry Antipov <dmantipov@yandex.ru>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings]
Date: Thu, 04 Sep 2014 08:59:35 +0400 [thread overview]
Message-ID: <5407F1B7.6090704@yandex.ru> (raw)
In-Reply-To: <540744F5.2010804@cs.ucla.edu>
On 09/03/2014 08:42 PM, Paul Eggert wrote:
> For GCC, we can define struct Lisp_Cons via 'struct __attribute__ ((aligned (GCALIGNMENT))) Lisp_Cons { ... };'.
> For compilers that don't support this syntax we can align the struct by hand, by using a character-array compound
> literal that's a bit too large, aligning the resulting pointer by hand, and then using the aligned pointer.
Yes, that seems to work:
Lisp_Object obj;
struct Lisp_Cons *c = ((struct Lisp_Cons *)
(((uintptr_t) (char [2 * sizeof (struct Lisp_Cons) - 1]) {}
+ (GCALIGNMENT - 1)) & ~(GCALIGNMENT - 1)));
c->car = Qnil;
c->u.cdr = Qnil;
XSETCONS (obj, c);
But I don't see how to fold this snippet into a macro which can be used as an rvalue, just like:
Lisp_Object obj = scoped_cons (Qnil, Qnil);
Dmitry
next prev parent reply other threads:[~2014-09-04 4:59 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-02 12:55 [RFC] temporary Lisp_Strings Dmitry Antipov
2014-09-02 13:21 ` Andreas Schwab
2014-09-02 13:47 ` Dmitry Antipov
2014-09-02 14:14 ` Andreas Schwab
2014-09-02 15:00 ` Eli Zaretskii
2014-09-02 14:00 ` Stefan Monnier
2014-09-02 15:13 ` Dmitry Antipov
2014-09-02 17:32 ` Stefan Monnier
2014-09-03 10:23 ` Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings] Dmitry Antipov
2014-09-03 13:14 ` Stefan Monnier
2014-09-03 14:39 ` Paul Eggert
2014-09-03 15:39 ` Dmitry Antipov
2014-09-03 16:42 ` Paul Eggert
2014-09-03 17:47 ` Stefan Monnier
2014-09-03 18:00 ` Paul Eggert
2014-09-04 4:59 ` Dmitry Antipov [this message]
2014-09-04 5:13 ` Paul Eggert
2014-09-04 5:51 ` Dmitry Antipov
2014-09-04 6:45 ` Paul Eggert
2014-09-04 13:11 ` Stefan Monnier
2014-09-04 13:37 ` Dmitry Antipov
2014-09-04 14:46 ` Dmitry Antipov
2014-09-04 16:03 ` Paul Eggert
2014-09-05 4:00 ` Dmitry Antipov
2014-09-05 4:24 ` Stefan Monnier
2014-09-05 9:28 ` Dmitry Antipov
2014-09-05 7:15 ` Paul Eggert
2014-09-05 9:16 ` Dmitry Antipov
2014-09-05 14:35 ` Paul Eggert
2014-09-05 15:35 ` Stefan Monnier
2014-09-08 10:33 ` Dmitry Antipov
2014-09-08 12:01 ` Dmitry Antipov
2014-09-08 13:30 ` Stefan Monnier
2014-09-08 12:44 ` Stefan Monnier
2014-09-08 13:30 ` Stefan Monnier
2014-09-02 14:37 ` [RFC] temporary Lisp_Strings Paul Eggert
2014-09-02 15:24 ` Dmitry Antipov
2014-09-02 15:28 ` Dmitry Antipov
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