From: Jeff Law <law@redhat.com>
To: Alexander Monakov <amonakov@ispras.ru>,
Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: Richard Biener <richard.guenther@gmail.com>,
GCC Patches <gcc-patches@gcc.gnu.org>, nd <nd@arm.com>
Subject: Re: [PATCH v2] Simplify pow with constant
Date: Fri, 25 Aug 2017 04:21:00 -0000 [thread overview]
Message-ID: <08021f24-4bbf-8897-fc28-6414a2810275@redhat.com> (raw)
In-Reply-To: <alpine.LNX.2.20.13.1708171835140.2420@monopod.intra.ispras.ru>
On 08/17/2017 09:43 AM, Alexander Monakov wrote:
> On Thu, 17 Aug 2017, Wilco Dijkstra wrote:
>
>> This patch simplifies pow (C, x) into exp (x * C1) if C > 0, C1 = log (C).
>
> Note this changes the outcome for C == +Inf, x == 0 (pow is specified to
> return 1.0 in that case, but x * C1 == NaN). There's another existing
> transform with the same issue, 'pow(expN(x), y) -> expN(x*y)', so this is
> not a new problem.
That may be part of the reason why they're guarded with -ffast-math. In
addition to the changes in accuracy. I haven't followed those
transformations on the GCC side to know with any certainty.
jeff
next prev parent reply other threads:[~2017-08-24 22:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-04 11:23 [PATCH] " Wilco Dijkstra
2017-08-04 12:26 ` Alexander Monakov
2017-08-04 12:44 ` Richard Biener
2017-08-04 15:28 ` Wilco Dijkstra
2017-08-17 14:19 ` [PATCH v2] " Wilco Dijkstra
2017-08-17 16:58 ` Alexander Monakov
2017-08-18 8:29 ` Richard Biener
2017-08-18 13:53 ` Wilco Dijkstra
2017-08-18 14:05 ` Richard Biener
2017-08-25 4:21 ` Jeff Law [this message]
2017-08-25 0:31 ` Jeff Law
2017-08-25 14:37 ` Wilco Dijkstra
2017-08-04 22:38 ` [PATCH] " Joseph Myers
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