| Re: [eigen] compile-time sqrt |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] compile-time sqrt
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Wed, 10 Feb 2010 19:57:33 -0500
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Hi,
The problem lies even deeper than that: ei_meta_sqrt takes an integer,
and actually floats can't be template parameters. So you can't use
ei_meta_sqrt for that.
In contexts where you're happy with just GCC, it's been able to
evaluate sqrt at compile time for a while. Since GCC 4.3, a lot more
functions are evaluated at compile time using MPFR. GCC 4.5 introduces
the same thing for complex numbers.
Thus, for lack of a better solution, you might just do a sqrt call and
rely on the compiler to optimize it at compile time.
An alternative is to compare x*x < eps instead of comparing x < sqrt(eps).
Benoit
2010/2/10 Thomas Capricelli <orzel@xxxxxxxxxxxxxxx>:
>
> Hi.
>
> I sometimes need to use sqrt of epsilon (typically in unsupported/Eigen/src/NonLinearOptimization/chkder.h)
> Currently i do
> const Scalar eps = ei_sqrt(NumTraits<Scalar>::epsilon());
>
> but i'd like to have it computed at compile-time.. i'm not sure how to do this. I've tried :
> const Scalar eps = ei_meta_sqrt<NumTraits<Scalar>::epsilon()>::ret;
>
> but the compiler complais that epsilon() is a function call hence the template can't be done.
>
> Thomas
> --
> Thomas Capricelli <orzel@xxxxxxxxxxxxxxx>
> http://www.freehackers.org/thomas
>
>
>