[Cfp-interest 2490] Re: 5.2.4.2.3 and IEC 60559

[Jim Thomas]

> On Aug 3, 2022, at 9:08 AM, Fred J. Tydeman <tydeman at tybor.com> wrote:
> 
> On Tue, 2 Aug 2022 09:56:10 +0200 Vincent Lefevre wrote:
>> 
>> On 2022-08-01 22:46:01 -0500, Fred J. Tydeman wrote:
>>> It appears to me that section 5.2.4.2.3 assumes that decimal floating point (DFP) is IEC 60559 DFP..
>>> Yet, I do not see such a requirement in 5.2.4.2.3.
>>> 
>>> I do see in 6.2.5#12 that the formats are IEC 60559 DFP.
>> 
>> I think that should also be put in 5.2.4.2.3.
>> 
>> BTW, does the standard clearly say that these types are optional?
>> This just seems to be suggested by 5.2.4.2.3, but 6.2.5#12 says
>> no more than "There are three decimal floating types, designated
>> as _Decimal32, _Decimal64, and _Decimal128. Respectively, they
>> have the IEC 60559 formats: decimal32, decimal64, and decimal128.
>> Decimal floating types are real floating types.", which could be
>> interpreted as such types being mandatory. Compare with _Complex,
>> for which it is said "Complex types are a conditional feature that
>> implementations need not support;".
>> 
>> Moreover, it seems that if one of these 3 types is supported, then
>> the 3 of them need to be supported. Is this wanted?
> 
> Page 183, 6.10.9.3 Conditional feature macros
> __STDC_IEC_60559_DFP__ The integer constant 202311L, intended to indicate support of decimal
> floating types and conformance to Annex F (IEC 60559 floating-point arithmetic) for
> decimal floating-point arithmetic.
> 
> Page 474, B.6.1  Characteristics of decimal floating types
> The following macros are provided only if the implementation defines __STDC_IEC_60559_DFP__ .
> N is 32, 64 and 128.
> DEC_INFINITY
> DECN_MANT_DIG
> DECN _MIN_EXP
> DECN _SNAN
> DEC_NAN
> DECN_MAX_EXP
> DECN _MIN
> DECN_EPSILON
> DECN_MAX
> DECN _TRUE_MIN
> 
> Page 547, #4 (H.2.1): "An implementation that defines __STDC_IEC_60559_DFP__
> provides the decimal floating types _Decimal32 , _Decimal64 , and
> _Decimal128 (6.2.5)."
> 
> Given the above, it seems to me that the first sentence in:
> 5.2.4.2.3 Characteristics of decimal floating types in <float.h>:
> 
> This subclause specifies macros in <float.h> that provide characteristics of decimal floating types
> in terms of the model presented in 5.2.4.2.2.
> 
> should be changed to:
> 
> This subclause specifies macros in <float.h> that provide characteristics of IEC 60559 decimal floating types
> (an optional feature) in terms of the model presented in 5.2.4.2.2.

Mention of IEC 60559 is not necessary. It doesn’t add anything.

I wouldn’t object to adding “(an optional feature)” but don’t think we should be asking for such local clarifications at this stage.

- Jim Thomas

> 
> 
> ---
> Fred J. Tydeman        Tydeman Consulting
> tydeman at tybor.com      Testing, numerics, programming
> +1 (702) 608-6093      Vice-chair of PL22.11 (ANSI "C")
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