Re: [Qemu-devel] [PATCH v4] fpu: add mechanism to check for invalid long double formats

[Andrew Dutcher]

I explicitly left the check off the comparison operations because I
misread the NaN check as something equivalent to the check I would be
adding. I'll add it shortly.

With regards to adding int32_indefinite, etc constants, I think I'll
leave it as is -- I'd prefer to have *what* happens clear (return this
number), then have *why* it happens be clear (return the integer
indefinite value).

And, finally, yes, I know what C++ and C-style comments are :P I just
think every argument I've ever read in favor of only using the latter
has been complete nonsense. Regardless! Guidelines are guidelines.

Thanks,
- Andrew

On Tue, Aug 16, 2016 at 6:34 AM, Peter Maydell <address@hidden> wrote:
> On 15 August 2016 at 23:27, Andrew Dutcher <address@hidden> wrote:
>> All operations that take a floatx80 as an operand need to have their
>> inputs checked for malformed encodings. In all of these cases, use the
>> function floatx80_invalid_encoding to perform the check. If an invalid
>> operand is found, raise an invalid operation exception, and then return
>> either NaN (for fp-typed results) or the integer indefinite value (the
>> minimum representable signed integer value, for int-typed results).
>>
>> Signed-off-by: Andrew Dutcher <address@hidden>
>> ---
>>
>> Version 4: Remove comments, since apparently it's still 1998. If anyone wants
>> to know what the value is for, they can check git blame.
>
> The code style gripe is not for having comments, it's for
> using the "//" style comment rather than "/* ... */". Yeah,
> we have some odd style requirements; at least we have a script
> which will detect them automatically. (By the way, you can run
> ./scripts/checkpatch.pl on your patch before sending it if you
> like; you don't have to wait for the patch robot to read your
> email :-))
>
> If you liked you could  define a constant for the 32-bit and
> 64-bit indefinite values rather than using 1 << 31 &c directly;
> 'return int32_indefinite;' is sufficiently self-documenting
> not to need a comment.
>
> I don't mind whether you do that, or not; your choice.
>
> The code changes you have here are good, but you've forgotten
> one piece: the comparison ops also need to handle the invalid
> encodings.
>
> floatx80_compare_internal() needs to raise float_flag_invalid
> and return float_relation_unordered if either of its inputs are
> invalid encodings.
>
> There are also separate single-comparison functions:
> floatx80_eq(), floatx80_le(), floatx80_lt(), floatx80_unordered(),
> floatx80_eq_quiet(), floatx80_le_quiet(), floatx80_lt_quiet(),
> floatx80_unordered_quiet(). The i386 guest doesn't use them but
> I think for consistency we should treat invalid encodings like
> NaNs there: raise float_flag_invalid and return 0.
>
> thanks
> -- PMM