Issue 0CFP.06: Part 1: fetestexceptflag and exceptions passed to fegetexceptflag

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: WG14, Jim Thomas
Date: 2016-09-10
Reference document: N2077
Submitted against: Floating-point TS 18661 (C11 version, 2014-2016)
Status: Fixed
Fixed in: C23
Converted from: n2397.htm

Summary

This is about the issue raised by Joseph Myers in email SC22WG14.14328:

TS 18661-1 says, for fetestexceptflag, "The value of *flagp shall have been set by a previous call to fegetexceptflag.".

This contrasts with the C11 wording for fesetexceptflag, "The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point exceptions represented by the argument excepts.".  So what happens if more exceptions are specified in the call to fetestexceptflag than were specified in the call to fegetexceptflag?  Then fegetexceptflag may or may not have stored any meaningful representation of the state of the extra exceptions being tested.

I think fetestexceptflag should have the same wording for this issue as fesetexceptflag: "whose second argument represented at least those floating-point exceptions represented by the argument excepts".

fesetexceptflag sets global state, typically a hardware register, whereas fetestexceptflag just reads a variable. It seems more important to avoid spurious data in the former.

Still, there’s no utility in testing spurious flag settings, and placing the same restrictions on fetestexceptflag as on fesetexceptflag might be less error prone.

Suggested Technical Corrigendum

In 15.2, in the new text for C 7.6.2.4a#2, change:

The value of *flagp shall have been set by a previous call to fegetexceptflag.

to:

The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point exceptions represented by the argument excepts.

Comment from WG14 on 2018-10-18:

Oct 2016 meeting

Committee Discussion

The committee agrees that this is a defect and accepts the Suggested Technical Corrigendum

Proposed Technical Corrigendum

In 15.2, in the new text for C 7.6.2.4a#2, change:

The value of *flagp shall have been set by a previous call to fegetexceptflag.

to:

The value of *flagp shall have been set by a previous call to fegetexceptflag whose second argument represented at least those floating-point exceptions represented by the argument excepts.