[Cfp-interest 3003] Fwd: [SC22WG14.24752] __STDC_WANT_IEC_60559_EXT__ and DFP interfaces

[Jim Thomas]

Here's another one to be added to CFP's C2Y issues list.

- Jim Thomas

> Begin forwarded message:
> 
> From: Joseph Myers <josmyers at redhat.com>
> Subject: [SC22WG14.24752] __STDC_WANT_IEC_60559_EXT__ and DFP interfaces
> Date: February 15, 2024 at 12:43:12 PM PST
> To: sc22wg14 at open-std.org
> 
> The following is a technical issue, so *not* something that can be 
> addressed now for C23, or indeed for C2y until we have a paper, or an 
> issue tracker with a relevant issue in it (it's now the 11th item on my 
> list of things to file in an issue tracker once we have one, as I think it 
> will be appropriate to handle through such an issue-handling mechanism), 
> but CFP should probably look at it.
> 
> Some decimal floating-point interfaces in <math.h> are conditional on the 
> user defining __STDC_WANT_IEC_60559_EXT__, but others aren't.  
> Specifically, _Decimal32_t, _Decimal64_t, HUGE_VAL_D32, HUGE_VAL_D64, 
> HUGE_VAL_D128 are conditional on the user defining that macro, while 
> DEC_INFINITY, DEC_NAN, FP_FAST_* for decimal types, and all functions 
> other than those in Annex F are not.
> 
> I don't think this division of dependency on that macro makes sense.  My 
> understanding of the intent of what was agreed after the October 2020 
> discussion of N2570 was that only the interfaces defined in Annex F should 
> be conditional on __STDC_WANT_IEC_60559_EXT__ - that is, the totalorder 
> and payload functions and CR_DECIMAL_DIG, but the decimal interfaces 
> enumerated above should not be so conditional.  (FE_SNANS_ALWAYS_SIGNAL is 
> in Annex F but *not* conditional on __STDC_WANT_IEC_60559_EXT__.  Since 
> FE_* is a reserved namespace for <fenv.h>, I think that's fine.)
> 
> -- 
> Joseph S. Myers
> josmyers at redhat.com
> 

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