From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Jeff Law <jeffreyalaw@gmail.com>
Cc: Andreas Schwab <schwab@suse.de>,
Jonathan Wakely <jwakely@redhat.com>,
libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [PATCH][risc-v] libstdc++: Preserve signbit of nan when converting float to double [PR113578]
Date: Tue, 7 May 2024 17:45:56 +0100 [thread overview]
Message-ID: <CAH6eHdSm=tfUKyrpX1KOOoAFk4kFp1sbi51FEr7GwJvS4AtBcQ@mail.gmail.com> (raw)
In-Reply-To: <CAH6eHdTx-QdmcNvxEVQPSEM3wcKz98-prpzo3LZz8DyJGp3-jA@mail.gmail.com>
On Tue, 7 May 2024 at 17:39, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>
> On Tue, 7 May 2024 at 17:33, Jeff Law wrote:
> >
> >
> >
> > On 5/7/24 9:36 AM, Andreas Schwab wrote:
> > > On Mai 07 2024, Jonathan Wakely wrote:
> > >
> > >> +#ifdef __riscv
> > >> + return _M_insert(__builtin_copysign((double)__f,
> > >> + (double)-__builtin_signbit(__f));
> > >
> > > Should this use static_cast<double>?
>
> Meh. It wouldn't fit in 80 columns any more with static_cast, and it
> means exactly the same thing.
>
> > And it's missing a close paren.
>
> Now that's more important! Thanks.
Also, I've just realised that signbit might return a negative value if
the signbit is set. The spec only says it returns non-zero if the
signbit is set.
So maybe we want:
#ifdef __riscv
const int __neg = __builtin_signbit(__f) ? -1 : 0;
return _M_insert(__builtin_copysign(static_cast<double>(__f),
static_cast<double>(__neg)));
#else
return _M_insert(static_cast<double>(__f));
#endif
next prev parent reply other threads:[~2024-05-07 16:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 13:49 Jonathan Wakely
2024-05-07 13:57 ` Jeff Law
2024-05-07 14:06 ` Jonathan Wakely
2024-05-07 14:11 ` Jonathan Wakely
2024-05-07 16:24 ` Palmer Dabbelt
2024-05-10 10:58 ` Jonathan Wakely
2024-05-07 15:25 ` Jeff Law
2024-05-07 15:36 ` Andreas Schwab
2024-05-07 16:31 ` Jeff Law
2024-05-07 16:39 ` Jonathan Wakely
2024-05-07 16:45 ` Jonathan Wakely [this message]
2024-05-08 10:32 ` Andrew Waterman
2024-05-08 10:40 ` Jonathan Wakely
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