Re: [eigen] fix double-promotion in 3.3 Core/SpecialFunctions.h

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

Thanks, the patch looks good, I pushed it. The first cast was not really 
necessary, I guess, but it does not hurt either.

I will also add the -Wdouble-promotion to our standard compile-flags. It 
looks like our code was mostly clean with regard to that (except some 
test-code which I will fix now).

I guess -Wconversion would also make sense (we already enable 
-Wshorten-64-to-32 on clang), but at the moment it generates too much 
noise. I'll probably add a bugzilla entry for that.

Cheers,
Christoph

On 2016-05-04 10:57, Ola Røer Thorsen wrote:
> Hi,
>
> I'm trying out the current Eigen default branch ("almost-3.3"), compiling
> code that has been using Eigen 3.2 until now.
>
> I'm using the GCC warnings -Wdouble-promotion and -Wfloat-conversion as
> these are really helpful to uncover performance bugs on some of the ARM
> CPUs I am using (only single-precision FPU, use of double is very slow).
>
> This uncovered some slight bugs in Core/SpecialFunctions.h where some
> expressions were using double-precision when they should use floats, such as
>
> extern/eigen3/Eigen/src/Core/SpecialFunctions.h:762:13: error: implicit
> conversion from 'float' to 'double' to match other operand of binary
> expression [-Werror=double-promotion]
>         c *= x/r;
>
> extern/eigen3/Eigen/src/Core/SpecialFunctions.h:767:25: error: conversion
> to 'float' from 'double' may alter its value [-Werror=float-conversion]
>       return (ans * ax / a);
>
> Attached here is a small patch that fixes the issues I found. It was
> created against the default branch as of this morning. I'm not experienced
> with Mercurial so I hope i made the file correctly - please let me know if
> it should be done differently.
>
> Best regards,
> Ola

--
 Dipl. Inf., Dipl. Math. Christoph Hertzberg

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