From: "Thompson, David" <dthompson2@worcester.edu>
To: Mark H Weaver <mhw@netris.org>
Cc: guile-devel <guile-devel@gnu.org>
Subject: Re: Attempting to unbox struct fields
Date: Mon, 29 Feb 2016 09:26:26 -0500 [thread overview]
Message-ID: <CAJ=RwfbDZ72urKO1Aa+epa7Q-OctzGfpDV4AKpxYb5=gcXhEsg@mail.gmail.com> (raw)
In-Reply-To: <87h9gscgpt.fsf@netris.org>
Hi Mark,
On Sun, Feb 28, 2016 at 10:56 PM, Mark H Weaver <mhw@netris.org> wrote:
> Hi David,
>
> "Thompson, David" <dthompson2@worcester.edu> writes:
>> Here's a patch I came up with to enable (and fix where necessary) the
>> support for signed integer and double struct fields.
>
> Great, thanks for working on it! This is not a proper review, just a
> couple of questions and comments.
I'm not very knowledgeable in the finer points of writing portable C
code or the Guile C API, so this feedback is very valuable. Thanks!
>> Am I on the right track here?
>
> The first thing I noticed is that the patch assumes that doubles are the
> same size as pointers. Obviously this is not the case on 32-bit
> systems. What's the plan for those systems?
Yeah, I just hacked this together on my x86_64 system and paid no mind
to portability. I was hoping that you or Andy or Ludovic would have
an idea for how to address portability issues. :)
> The patch also currently assumes that longs and pointers are the same
> size, and this turns out to be false on LLP64 systems such as 64-bit
> Windows. See <https://debbugs.gnu.org/22406>. However, it should be
> straightforward to fix this issue.
>
>> + if ((prot != 'r' && prot != 'w') || inits_idx == n_inits)
>> + *mem = 0.0;
>
> Note that 'mem' is of type scm_t_bits*, so the 0.0 will be converted to
> the integer 0 and then stored as an integer, which I guess is not what
> you meant. Note that in practice this works on IEEE 754 systems, where
> 0.0 is represented as all zero bits, but the code is somewhat misleading
> and less portable than it could be.
D'oh! I forgot to cast here. Thanks for the explanation. It
explains why I didn't notice the issue when testing.
My current plan is to keep pressing onward and produce a
proof-of-concept, hacky patch set that allows unboxed struct fields on
x86_64. Then, with some help and guidance, I can sort out the
portability issues, code style issues, unit tests, and documentation
after confirmation that the prototype is on the right track.
Thanks,
- Dave
next prev parent reply other threads:[~2016-02-29 14:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-28 15:03 Attempting to unbox struct fields David Thompson
2016-02-28 21:30 ` Thompson, David
2016-02-29 3:56 ` Mark H Weaver
2016-02-29 14:26 ` Thompson, David [this message]
2016-02-29 17:43 ` Mark H Weaver
2016-02-29 21:09 ` Thompson, David
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