[J3] Draft interp on mathematical equivence

[John Reid]

Thomas,

I am not opposed to adding a non-normative note. It could be added as an 
option for J3 to choose..

John.


Thomas König wrote:
> John,
>
>> I have been contacted by Michael Rutter of Cambridge University over 
>> an issue that concerns him and some of the developers of gfortran.
>>
>> Almost all current computers support signed zeros and NaNs and the 
>> Standard mentions them in several places, for example, 7.4.3.2, 
>> 13.7.2.3.5,  16.9.22, 16.9.128, 16.9.189, 16.9.195. Some gfortran 
>> developers became convinced that the Standard required real-complex 
>> multiplication to be performed by first converting the real to 
>> complex, even if it involved a performance penalty, because the 
>> result can differ in the presence of NaNs and signed zeros. We 
>> believe that the performance penalty is not required because the 
>> Standard allows the use of a mathematically equivalent expression. It 
>> hinges on the exact meaning of mathematical equivalence. We see no 
>> need for edits to the Standard, but do see a formal interpretation as 
>> necessary to resolve the issue among the gfortran developers.
>>
>> Our draft interp is attached. Do you have any comments before I send 
>> it in?
>
> Thank you for taking this on, and for the clarification.
>
> Since there is obvious room for different interpretations in the text
> "as is" (or the question would not have arisen), what do you think about
> adding a non-normative note?
>
> Best regards
>
>     Thomas
>
>