Re: [Qemu-devel] [PATCH] softfloat: rename make_float[x80|128]_init to const_float[x80|128]

[Eric Blake]

On 09/19/2017 11:30 AM, Richard Henderson wrote:
> On 09/18/2017 05:46 AM, Laurent Vivier wrote:
>> Redefine make_floatx80() and make_float128() as make_float16(),
>> make_float32() and make_float64() using a variable and not only
>> a cast.

>> -#define make_floatx80(exp, mant) ((floatx80) { mant, exp })
>> -#define make_floatx80_init(exp, mant) { .low = mant, .high = exp }
>> +#define make_floatx80(exp, mant) __extension__ \
>> +    ({ floatx80 f80_val = { .low = mant, .high = exp }; f80_val; })
>> +#define const_floatx80(exp, mant) { .low = mant, .high = exp }

> 
> I don't like this part -- (type){ init } is a standard C99 compound literal.
> There's no point using a gcc extension instead.

The C99 compound literal is not a const initializer in all situations,
though :(  Here's another thread where we had a similar discussion, but
there, the solution was to just make the macro behave as an initializer
(which is C99 compliant, but loses some type safety) instead of relying
on a gcc extension:

https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg06566.html

I suspect you're running into the same issues that Laszlo already helped
us understand regarding QLit.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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