Status of fenv.h header and floating point environment support in newlib

[Joel Sherrill]

Ayush please add yourself to  https://devel.rtems.org/wiki/GSoC/2020.

Vaibhav.. we haven't asked others to add themselves to the table.
Please ping anyone we missed.

On the fenv.h side, there are some basic guidelines on how to provide
the fenv functionality and subtleties from the POSIX requirements.

First, the preferred origin of the implementation is another open source
project with FreeBSD and NetBSD being at the top of the list. For example,
here is the NetBSD implementation for the m68k:

https://github.com/NetBSD/src/blob/trunk/sys/arch/m68k/include/fenv.h

But there are differences between vanilla m68k and coldfire so that may
not support all CPU variations. Would have to be determined.

I have not found a SPARC implementation with an appropriate license.
Jiri may have a better source.

I would put ARM, PowerPC, and MIPS at the top of the desired list that we
should be able to find BSD implementations for. We don't have an aarch64
port yet but I wouldn't stop a GSoC student from adding it to newlib. Just
can't
be tested with RTEMS yet. Beyond that, architectures like the m68k where it
is porting, not writing from scratch are priorities. Covering as many
architectures
that are popular with RTEMS is the goal. SPARC64 would be down the list
based on that.

Next POSIX allows an implementation to not support much if it isn't there
in hardware.

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fenv.h.html#tag_13_12


The fact that an architecture may not support a feature is challenging to
testing.

--joel

On Mon, Feb 17, 2020 at 5:54 AM Jiri Gaisler <jiri at gaisler.se> wrote:

>
> On 2/17/20 11:16 AM, Vaibhav Gupta wrote:
>
>
>
> On Mon, Feb 17, 2020, 3:07 PM Ayush Dwivedi <21cencturyayush at gmail.com>
> wrote:
>
>> Hello Joel,
>> This is regarding the open project #2966 POSIX-Compliance #2971( Add
>> fenv.h to newlib). The task is about adding the floating point environment
>> header to the newlib library but the source code of the library already has
>> the header with the listed function declarations and data struct as needed.
>> The implementations for the following architectures are available in the
>> newlib-cygwin repository:
>> >RISCV
>> >i386
>> >x86_64
>> As pointed out in the POSIX Compliance project sub-task page the
>> implementations for following architectures are yet to be added:
>> >ARM(software float implementation for this exists but no fenv
>> implementation)
>> >AArch64(software float implementation for this exists but no fenv
>> implementation)
>> >SPARC and SPARC64(directories for these architectures are missing from
>> libm/machine/ so no implementation of any sort)
>>
>> I would like to try and implement the functions declared in the header
>> using BSD libc of FreeBSD as reference for the ARM and SPARC architectures.
>>
>> Following is the output after running test for posix fenv
>> header(psxfenv01.exe) for SPARC using sparc-rtems5-sis and
>> sparc-rtems5-gdb.(The Test failed)
>>
> Yes because testsuite needs modifications and moreover fenv on SPARC is
> not yet supported. Since the support for RISCV and x86_64 is present, you
> can make a testsuite for them. You can use qemu for running riscv files.
>
> Note that sis (riscv-rtems5-sis) also supports RISCV32 using the griscv
> BSP in RTEMS.
>
> Jiri.
>
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