Defect Report #426

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Submitter: Fred J. Tydeman
Submission Date: 2013-01-07
Source: WG 14
Reference Document: N1670
Version: 1.1
Date: October 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:

I believe it matters for at least these cases:

  1. 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.
  2. 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.
  3. 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

Oct 2013 meeting

Committee Discussion

Proposed Technical Corrigendum

In the table in G.5.1 #2, change

-yv

to

(-y)v
in three places.

In the table in G.5.1 #3, change

-x/v

to

(-x)/v
in two places.


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