[J3] Draft interp on mathematical equivence

[Thomas König]

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