|
From: | Dmitry Antipov |
Subject: | Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings] |
Date: | Thu, 04 Sep 2014 08:59:35 +0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 |
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
[Prev in Thread] | Current Thread | [Next in Thread] |