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[Bug target/32392] Support using -mrecip w/o additional Newton-Raphson run
- From: "burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 18 Jun 2007 15:03:09 -0000
- Subject: [Bug target/32392] Support using -mrecip w/o additional Newton-Raphson run
- References: <bug-32392-13404@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #1 from burnus at gcc dot gnu dot org 2007-06-18 15:03 -------
Initial suggestion, see:
http://gcc.gnu.org/ml/gcc-patches/2007-06/msg01068.html
Richard's remark:
http://gcc.gnu.org/ml/gcc-patches/2007-06/msg01224.html
> Two NR steps don't make sense, they wouldn't improve accuracy because of the
> extra roundings we get for the NR. And of course it would be slower.
(However, two NR are said to be enough for double precision. I don't know
whether doing rsqrt+(2x NR) is faster than 1/sqrt() for double or not.)
Related - closed - PRs:
PR 31723 - Use reciprocal and reciprocal square root with -ffast-math (FIXED)
PR 32352 - Using rsqrt, Polyhedron's aermod test crashes (WONTFIX)
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32392