[SOLVED] Are HAS_SUBNORM and __STDC_IEC_559_

Are HAS_SUBNORM and __STDC_IEC_559__ dependent?

Are HAS_SUBNORM and __STDC_IEC_559__ dependent? For example:

If __STDC_IEC_559__ is 1, then HAS_SUBNORM is 1.
If HAS_SUBNORM is 0, then __STDC_IEC_559__ is not 1.

Solution

Are HAS_SUBNORM and __STDC_IEC_559__ dependent?

I'd suggest no.
__STDC_IEC_559__ == 1 and xxx_HAS_SUBNORM != 1 possible.

C17 Appendix F specifies what is needed to conform to __STDC_IEC_559__: "An implementation that defines __STDC_IEC_559__ shall conform to the specifications in this annex."

Appendix F does not specify support of subnormal's and even has in 2 places describing functions:

... When subnormal results are supported, the returned value is exact and is independent of the current rounding direction mode. C17dr § F.10.7.2&3 2.

This at least implies subnormal support is not required for those functions. Also see @Ian Abbott

Nit:

"__STDC_IEC_559__ is not 1." is more like "__STDC_IEC_559__ not defined", not "if defined and not 1".