[J3] IEEE Std 754-2019

[Robert Corbett]

David Hough expressed hope that the new edition of the IEEE floating-point standard will be publicly available by the end of this month.  The previous edition took about two and a half years to go from being published by IEEE to being published as an ISO/IEC/IEEE standard.

The new floating-point standard raises some issues for the Fortran standard.  The text of Clause 17 needs to be checked for consistency with the new f.p. standard.  Then there is the matter of new features.  The new f.p. standard includes a new rounding mode and some new operations intended to support "reproducible floating-point arithmetic".  There is an ongoing effort to define and implement libraries that should produce the same results for a variety of hardware and software platforms.  Whether that effort will succeed and whether the resulting libraries will see significant use is unclear.

The new features of the f.p. standard require hardware support for efficient implementation.  I do not know of any processor vendors who have announced that they intend to support the new features.

The new features of the f.p. standard could be regarded solely as support features for reproducible arithmetic.  If considered as such, a case could be made for not making those features available in Fortran.

The next edition of the Fortran standard should ensure that the features provided in Clause 17 are consistent with the new edition of the f.p. standard.

I think there is sufficient doubt about the new features of the f.p. standard to recommend against adding support for them in the next edition of the Fortran standard.  If hardware vendors announce support for the new features, I would reconsider my recommendation.

Robert Corbett