soft-fp: Add FP_DENORM_ZERO

[Carlos O'Donell]

On 10/08/2014 08:57 PM, Joseph S. Myers wrote:
> On Wed, 8 Oct 2014, Carlos O'Donell wrote:
> 
>>> diff --git a/soft-fp/soft-fp.h b/soft-fp/soft-fp.h
>>> index 86bc7fa..05fcca0 100644
>>> --- a/soft-fp/soft-fp.h
>>> +++ b/soft-fp/soft-fp.h
>>> @@ -161,6 +161,11 @@
>>>  # define FP_HANDLE_EXCEPTIONS do {} while (0)
>>>  #endif
>>>  
>>> +/* Whether to flush subnormal inputs to zero with the same sign.  */
>>> +#ifndef FP_DENORM_ZERO
>>> +# define FP_DENORM_ZERO 0
>>> +#endif
>>
>> OK, but...
>>
>> For the record this is an instance of the "centralized defaults" pattern
>> which we try to avoid in glibc. What if the target accidentally defines:
> 
> I am unconvinced this can readily be avoided in the soft-fp code without a 
> lot of duplication of common definitions in different sfp-machine.h files 
> (of which there are a lot, when you consider those in libgcc and the Linux 
> kernel as well as glibc).

I am not sufficiently familiar with the code to make that judgement, I was
only noting that we're trying to avoid that kind of pattern in glibc in
general. However, "in general" may not apply to this specific case for
soft-fp.

Cheers,
Carlos.