From: Martin Jambor <mjambor@suse.cz>
To: Tejas Joshi <tejasjoshi9673@gmail.com>, gcc@gcc.gnu.org
Cc: hubicka@ucw.cz
Subject: Re: About GSOC.
Date: Thu, 30 May 2019 17:08:00 -0000 [thread overview]
Message-ID: <ri6muj3amzm.fsf@suse.cz> (raw)
In-Reply-To: <CACMrGjB41A2BSPJqGs3ckH+w4xX6iXyc7Kk1siPYFm-TreKWjg@mail.gmail.com>
Hi,
On Thu, May 30 2019, Tejas Joshi wrote:
> Hello.
> I tried to check the values for significand words using _Float128
> using a test program with value larger than 64 bit.
> Test program :
>
> int main ()
> {
> _Float128 x = 18446744073709551617.5; (i.e. 2^64 + 1.5 which is
> certainly longer than 64-bit)
> _Float128 y = __builtin_roundf128 (x);
> }
Interesting, I was also puzzled for a moment. But notice that:
int main ()
{
_Float128 x = 18446744073709551617.5f128;
_Float128 y = __builtin_roundf128 (x);
}
behaves as expected... the difference is of course the suffix pegged to
the literal constant (see
https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Floating-Types.html).
I would also expect GCC to use a larger type if a constant does not fit
into a double, but apparently that does not happen. I would have to
check but it is probably the right behavior according to the standard.
>
> The lower words of significand (sig[1] and sig[0] for 64-bit system)
> are still being zero. I haven't included the roundevenf128 yet but
> inspecting this on real_round function.
I figured out what was going on when I realized that in your testcase,
sig[0] was equal to 0x8000000000000000 and so some precision has been
lost. Then it was easy to guess that it was because it was represented
in a narrower type.
Hope this helps,
Martin
next prev parent reply other threads:[~2019-05-30 17:08 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CACMrGjCeaZ7EoYqjLYiAJXjOtOfpJNo9zcbWhfarfkiLMN8YYA@mail.gmail.com>
2018-10-13 4:43 ` Tejas Joshi
2018-10-23 10:47 ` Martin Jambor
2018-10-23 16:51 ` Joseph Myers
2018-11-16 16:50 ` Tejas Joshi
2018-11-16 19:00 ` Joseph Myers
2019-01-21 19:13 ` Tejas Joshi
2019-01-21 23:03 ` Joseph Myers
2019-01-23 2:55 ` Tejas Joshi
2019-01-23 4:00 ` Tejas Joshi
2019-01-23 17:37 ` Joseph Myers
2019-01-25 19:52 ` Tejas Joshi
2019-01-25 21:32 ` Joseph Myers
2019-01-28 17:00 ` Tejas Joshi
2019-02-04 14:39 ` Tejas Joshi
2019-02-04 15:06 ` Prathamesh Kulkarni
2019-02-04 15:56 ` Tejas Joshi
2019-02-04 16:44 ` Prathamesh Kulkarni
2019-02-04 17:22 ` Tejas Joshi
2019-02-24 12:05 ` Tejas Joshi
2019-03-30 11:24 ` Tejas Joshi
2019-04-01 19:53 ` Joseph Myers
2019-04-04 13:04 ` Tejas Joshi
2019-05-04 11:20 ` Tejas Joshi
2019-05-07 17:18 ` Joseph Myers
2019-05-07 19:38 ` Tejas Joshi
2019-05-07 21:01 ` Joseph Myers
2019-05-08 3:27 ` Tejas Joshi
2019-05-08 7:30 ` Tejas Joshi
2019-05-08 14:21 ` Tejas Joshi
2019-05-09 17:01 ` Joseph Myers
2019-05-09 16:55 ` Joseph Myers
2019-05-20 15:49 ` Martin Jambor
2019-05-20 21:48 ` Joseph Myers
2019-05-29 11:21 ` Tejas Joshi
2019-05-29 18:45 ` Tejas Joshi
2019-05-30 17:08 ` Martin Jambor [this message]
2019-05-30 21:38 ` Segher Boessenkool
2019-05-31 10:11 ` Martin Jambor
2019-05-31 10:28 ` Tejas Joshi
2019-06-03 16:38 ` Joseph Myers
2019-06-04 7:03 ` Tejas Joshi
2019-06-05 12:19 ` Tejas Joshi
2019-06-06 16:43 ` Joseph Myers
2019-06-09 4:48 ` Tejas Joshi
2019-06-10 20:26 ` Joseph Myers
2019-06-12 18:52 ` Tejas Joshi
2019-06-13 12:33 ` Tejas Joshi
2019-06-13 17:19 ` Expanding roundeven (Was: Re: About GSOC.) Martin Jambor
2019-06-13 21:16 ` Joseph Myers
2019-06-14 12:49 ` Tejas Joshi
2019-06-14 17:32 ` Martin Jambor
2019-06-17 7:50 ` Tejas Joshi
2019-06-17 17:15 ` Joseph Myers
2019-06-19 13:32 ` Tejas Joshi
2019-06-22 17:11 ` Tejas Joshi
2019-06-22 17:37 ` Jan Hubicka
2019-06-17 17:10 ` Joseph Myers
2019-05-31 11:13 ` About GSOC Segher Boessenkool
2019-05-31 11:16 ` Nathan Sidwell
2019-05-31 13:30 ` Eric Gallager
2019-06-03 9:37 ` Tejas Joshi
2019-06-06 16:56 ` Committing patches and other conventions (Was: Re: About GSOC) Martin Jambor
2019-06-09 4:57 ` Tejas Joshi
2019-06-12 13:48 ` Tejas Joshi
2019-06-13 17:02 ` Martin Jambor
2024-03-04 6:57 About gsoc mokshagnareddyc
2024-03-04 10:06 ` Jonathan Wakely
2024-03-05 2:02 ` Dave Blanchard
2024-03-05 9:31 ` Jonathan Wakely
2024-03-05 9:32 ` Jonathan Wakely
2024-03-11 1:17 ` Dave Blanchard
2024-03-11 9:08 ` Mark Wielaard
2024-03-07 12:26 ` Martin Jambor
2024-03-11 12:41 Julian Waters
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
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ri6muj3amzm.fsf@suse.cz \
--to=mjambor@suse.cz \
--cc=gcc@gcc.gnu.org \
--cc=hubicka@ucw.cz \
--cc=tejasjoshi9673@gmail.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.
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).