Submitter:Fred Tydeman
Submission Date: 2018-12-12
Document: WG14 N2319
Reference Documents: N2124

Summary

There are (at least) two kinds of round to nearest. For FLT_ROUNDS to reflect the execution-time rounding mode, each of the round to nearest choices needs to be possible values of FLT_ROUNDS.

Technical Corrigendum:

Change §5.2.4.2.2#9 from

The rounding mode for floating-point addition is characterized by the implementation-defined value of FLT_ROUNDS:23) 
-1 indeterminable
 0 toward zero
 1 to nearest
 2 toward positive infinity
 3 toward negative infinity

to:

The rounding mode for floating-point addition is characterized by the implementation-defined value of FLT_ROUNDS: 
-1 indeterminable
 0 toward zero
 1 to nearest, ties to even
 2 toward positive infinity
 3 toward negative infinity
 4 to nearest, ties away from zero

and remove:

*) The value 1 is intended for any mode that rounds to nearest, regardless of how it rounds halfway cases.
from the footnote that was added by n2124.

Also, move existing footnote 23

23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through the function fesetround in <fenv.h>.

to be part of paragraph 9.

Change §7.6, paragraph 8 from:

Each of the macros 
   
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD

is defined if and only if the implementation supports getting and setting the represented rounding direction by means of the fegetround and fesetround functions.

to:

Each of the macros 
   
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD
FE_TONEARESTFROMZERO

is defined if and only if the implementation supports getting and setting the represented rounding direction by means of the fegetround and fesetround functions.

I need to see Annex F after TS 18661-1 is applied to see if any references to FLT_ROUNDS there need to be changed.