[Cfp-interest 1299] N2323

[Fred J. Tydeman]

On Mon, 22 Apr 2019 10:08:28 -0700 Jim Thomas wrote:
>
>> N2323<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2323.htm> 2018/12/10 Tydeman, SD3 1: DR 440: Test macros for FP being 754 types
>
>Agree with the need at least for a macro to say whether long double has an IEC 60559 format for annex F implementations.  
>
>What does " operations are those of an IEC 60559 basic, interchange or extended format" mean? Of what use is it without a binding? Interchange formats include basic formats. What if format is IEC 60559 but operations are not? Why mention operations?

I got those words from Joseph Myers N1730 paper that proposed this solution.
What do we want to do about implementations that use IEC formats, but not all values and/or operations?
There are hardwares that flush denormals to zero, yet use IEC format.

>IEC 60559 itself has formats, not types. 

OK, but I think there is no mention of IEC 60559 types.

>Does saying the type's values are those of an IEC 60559 type/format mean that subnormals and signed zeros and infinities are values of the type?

Yes

>How about just saying
>
>0      type does not have an IEC 60559 format
>1      type has an IEC 60559 format
>
>The number for bits in an IEC 60559 extended format is not defined.

OK.  But, each implementation will pick some number of bits .
So, for example:
LDBL_IS_IEC_60559 80
would apply to Intel's 80 bit format (which is double extended).


---
Fred J. Tydeman        Tydeman Consulting
tydeman at tybor.com      Testing, numerics, programming
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