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Re: Patch to add missing PPC instruction
- From: degger at fhm dot edu
- To: dje at watson dot ibm dot com
- Cc: gcc-patches at gcc dot gnu dot org, gcc at gcc dot gnu dot org
- Date: Mon, 17 Dec 2001 22:28:49 +0100 (CET)
- Subject: Re: Patch to add missing PPC instruction
- Reply-to: degger at fhm dot edu
On 17 Dec, David Edelsohn wrote:
> fres is floating-point reciprocal ESTIMATE Single, not a
> single-precision reciprocal.
Right, I got that wrong.
> It is accurate to one part in either 256 or 4096,
According to the PPC Programming Environment manual page 8-88,
the error is less or equal to 1/256.
> not IEEE 754 Single Precision accuracy.
A candidate for -ffast-math? I originally meant it that way but forgot
about it between the time I wrote the patch and sent it here
(>4 months).
For some applications (those who are using single precision arithmetics)
it might actually be enough to such an unaccurate reciprocal but I
definitely see your point when you say it's not acceptable to be used in
general.
--
Servus,
Daniel