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Date: Tue, 02 Dec 2014 20:13:27 +0100
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: Re: [PATCH 2/4] cimag and friends shouldn't return an lvalue
Am Dienstag, den 02.12.2014, 12:58 -0500 schrieb Rich Felker:
> On Tue, Nov 25, 2014 at 03:49:55PM +0100, Jens Gustedt wrote:
> > This is nothing imperative, but is a bit more user friendly, because it
> > should error out in situations that a user of these macros can't expect
> > to work.
> >
> > If __GNU__ is detected, this uses the "__imag__" extension of gcc and
> > friends. This should be the less costly solution. It should not create a
> > temporary object, even in absence of optimization. This extension is
> > arround in all versions of gcc that provide complex arithmetic.
> > ---
> > include/complex.h | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/complex.h b/include/complex.h
> > index 3e14e04..be5bd7e 100644
> > --- a/include/complex.h
> > +++ b/include/complex.h
> > @@ -101,8 +101,13 @@ double creal(double complex);
> > float crealf(float complex);
> > long double creall(long double complex);
> >
> > +#ifdef __GNUC__
> > +#define __CIMAG(x, t) \
> > + (__extension__ __imag__ (_Complex t)(x))
> > +#else
> > #define __CIMAG(x, t) \
> > - ((union { _Complex t __z; t __xy[2]; }){(_Complex t)(x)}.__xy[1])
> > + (+(union { _Complex t __z; t __xy[2]; }){(_Complex t)(x)}.__xy[1])
> > +#endif
>
> Short of a good reason to need the GNU-specific version (like subtle
> non-conformance, performance issues, or other problems in the portable
> version),
no temporary would be a reason for me, and using the tool that is
forseen by the compiler makers would be another
but I don't have a strong opinion on that
Jens
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