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Re: Make ARM fesetenv (FE_NOMASK_ENV) detect failure (bug 14866)
On 11/21/2012 02:08 PM, Joseph S. Myers wrote:
> On Wed, 21 Nov 2012, Richard Henderson wrote:
>
>> On 11/21/2012 12:28 PM, Joseph S. Myers wrote:
>>> + if (envp == FE_NOMASK_ENV)
>>> + {
>>> + /* VFPv3 and VFPv4 do not support trapping exceptions, so
>>> + test whether the relevant bits were set and fail if
>>> + not. */
>>> + _FPU_GETCW (temp);
>>> + if ((temp & _FPU_IEEE) != _FPU_IEEE)
>>> + return 1;
>>> + }
>>
>> Why test vs FE_NOMASK_ENV explicitly? In theory the exception value
>> could have come from just about anywhere.
>
> The fesetenv argument must either be one of the macros from fenv.h, or an
> environment previously obtained from one of the fenv.h functions in the
> same execution of the same program (and in the latter case, if these bits
> are set it means the processor supports them).
>
Yeah, but the fine point of "same execution same program" could easily be
missed. I was thinking of a distributed system containing a mix of VFPv2/v3
processors, in which fenv_t values were shared across nodes.
Not so very likely, but why not program more robustly? Especially if, as I
suspect, the more robust formulation actually results in fewer insns?
r~