From: Segher Boessenkool <segher@kernel.crashing.org>
To: Roger Sayle <roger@eyesopen.com>
Cc: gcc@gcc.gnu.org, "Kaveh R. Ghazi" <ghazi@caip.rutgers.edu>
Subject: Re: Question on valid transformations for cbrt
Date: Wed, 10 Mar 2004 15:32:00 -0000 [thread overview]
Message-ID: <0564E1F0-72A8-11D8-98DF-000A95A4DC02@kernel.crashing.org> (raw)
In-Reply-To: <Pine.LNX.4.44.0403070640560.29012-100000@www.eyesopen.com>
> The problem with cbrt, unlike sqrt, is that its is more expressive than
> pow. i.e. cbrt(-29.7) = -3.1 but pow(-29.7,1.0/3.0) => EDOM. Hence
> we can't normalize cbrt(x) as pow(x,1.0/3.0),
You can "normalize" cbrt(x) as sign(x) * pow(abs(x), 1.0/3) -- maybe
that
helps some further optimizations?
> but we can safely go the
> other way pow(x,1.0/3.0) => cbrt(x).
Segher
next prev parent reply other threads:[~2004-03-10 15:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-06 18:54 Kaveh R. Ghazi
2004-03-07 15:11 ` Roger Sayle
2004-03-10 15:32 ` Segher Boessenkool [this message]
2004-03-10 16:06 ` Robert Dewar
2004-04-02 0:22 ` Geoff Keating
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