Re: round() on arm vs aarch64

Re: round() on arm vs aarch64

[Richard Earnshaw]

On 03/11/2022 14:13, Joel Sherrill wrote:
> Hi
> 
> This is likely not a newlib bug but I thought I would start here because
> I'm not sure what is going on and I thought someone on this list would have
> an idea: This is a simple C++ function that calls std::round. It compiles
> on arm but aarch64 says round isn't in the std namespace.
> 
> If you change the program to just use round() and not std::round() it
> compiles on both architectures.
> 
> The compiler versions are the same and report:
> 
> arm-rtems6-gcc (GCC) 12.2.1 20221014 (RTEMS 6, RSB
> cb8821e93378118e78a9cb25859789b126bd5761, Newlib 0b6342c)
> 
> =====================
> $ cat r.cc
> #include <cmath>
> 
> 
> 
> int wrap(double v)
> 
> {
> 
>    double r = std::round((float)v);
> 
>    return (r > 0);
> 
> }
> 
> [joel@devel round]$ arm-rtems6-gcc -Wall -c r.cc
> [joel@devel round]$ aarch64-rtems6-gcc -Wall -c r.cc
> r.cc: In function 'int wrap(double)':
> r.cc:5:19: error: 'round' is not a member of 'std'; did you mean 'round'?
>      5 |   double r = std::round((float)v);
>        |                   ^~~~~
> In file included from
> /home/joel/rtems-work/tools/6/lib/gcc/aarch64-rtems6/12.2.1/include/c++/cmath:45,
>                   from r.cc:1:
> /home/joel/rtems-work/tools/6/aarch64-rtems6/include/math.h:337:15: note:
> 'round' declared here
>    337 | extern double round (double);
> =====================
> 
> Any ideas what would cause this?
> 
> Thanks
> 
> --joel

Have you tried comparing the pre-processed output from the two versions? 
  It might give a clue as to what's going on.

R.

Re: round() on arm vs aarch64

[Stephanos Ioannidis]

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On Tue, 2022-11-15 at 09:38 -0600, Joel Sherrill wrote:
> Digging a bit, I noticed a huge block of <cmath> is ifdef'ed out for
> aarch64.
> I found the file c++config.h which is different between the two.
> 
> Based on the diff of the arm and aarch64 versions, arm has
>  _GLIBCXX_USE_C99_MATH_TR1 defined but aarch64 does not.
> 
> I have no idea where the settings in this file come from but this
> appears to be the key difference.
> 
> More insight appreciated.

Funny how I came across a similar issue today. The following link might
be of help in understanding what is going on:

https://github.com/zephyrproject-rtos/sdk-ng/issues/566#issuecomment-1315165640

Regards,

Stephanos

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