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Re: round-off error in std::pow(std::complex<T>, double) in C++11

From: Paolo Carlini <paolo dot carlini at oracle dot com>
To: Jordi Gutiérrez Hermoso <jordigh at octave dot org>
Cc: Gabriel Dos Reis <gdr at integrable-solutions dot net>, Ed Meyer <eem2314 at gmail dot com>, libstdc++ at gcc dot gnu dot org, Octave Maintainers List <octave-maintainers at octave dot org>
Date: Fri, 25 Jan 2013 16:44:03 +0100
Subject: Re: round-off error in std::pow(std::complex<T>, double) in C++11
References: <CAPHS2gyA32jcz9mgCLicWRbULNKSRr63jGDbfhXRHo_Zi2WyEA@mail.gmail.com> <alpine.DEB.2.02.1301231611430.3767@laptop-mg.saclay.inria.fr> <CAPHS2gzF6d01ibHT_a4T8nPe03-7=ZZmsUnYRYz5WLhOxC4Hiw@mail.gmail.com> <alpine.DEB.2.02.1301232228160.3767@laptop-mg.saclay.inria.fr> <CAAiZkiAFt99teD=eVSBWFtcoAwE4etaaRHBj+=-KaC00kCk2MA@mail.gmail.com> <CAKWV3Rp9i0K+TxvD-=FovxoPAhZK_LS1ftDmu+JViPUaC7KmmA@mail.gmail.com> <CAAiZkiDViJCC2PP2sLTqq61Pv1pF3L6iJaYHJCTx=tJWk-C=EQ@mail.gmail.com> <CAPHS2gwUPpDzkVD7FvkU_MiVVGWrKE6Zgick-SqeBQYO51w8Ew@mail.gmail.com> <5102A1A1.9010706@oracle.com>

.. oops, I just noticed what Marc suggested in the PR about changing pow(const complex<>&, const _Tp&) to *actually* forward to the complex builtins when not fast math. That seems a good idea, because we are normally *not* forwarding directly to the builtins in this specific mixed case, sorry I was wrong. I'd like to ear Gaby about this, however, because even for not fast math it seems a bit weird to not exploit the knowledge that the exponent is real...

Paolo.

Follow-Ups:
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Paolo Carlini

References:
- round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Jordi GutiÃrrez Hermoso
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Marc Glisse
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Jordi GutiÃrrez Hermoso
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Marc Glisse
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Gabriel Dos Reis
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Gabriel Dos Reis
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Jordi GutiÃrrez Hermoso
- Re: round-off error in std::pow(std::complex<T>, double) in C++11
  - From: Paolo Carlini

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