Defect Report #426
Previous Defect Report < - > Next Defect Report
Submitter: Fred J. Tydeman
Submission Date: 2013-01-07
Source: WG 14
Reference Document: N1670
Version: 1.0
Date: April 2013
Subject: G.5.1: -yv and -x/v are ambiguous
Summary
The tables in G.5.1 have the mathematical formulas -yv and
-x/v. I believe that they are ambiguous as they could have two
meanings:
- (-y)/v and (-x)/v
- -(y/v) and -(x/v)
I believe it matters for at least these cases:
- The two operands are different NaNs, negate flips the sign
of a NaN, and the result of * and / depends upon the sign and
value of the NaN.
- The result is a NaN from non-NaN operands, negate does not
flip the sign of a NaN, while both * and / set the sign of the
result as the XOR of the signs of the operands.
- All operands are non-NaN, the result is inexact and
non-NaN, and a rounding that is not symmetric about zero is in
effect.
Suggested Technical Corrigendum
Apr 2013 meeting
Committee Discussion
- The committee sees the mathematical formulae as unambiguous since the regroupings presented in the paper are mathematically equivalent, and should not be construed as C expressions. As such, there was considerable skepticism expressed that this was indeed a defect.
- The author promised to provide a supplemental paper that would substantiate his concern about this as a defect.
Previous Defect Report < - >
Next Defect Report