# RE: [XQuery] IBM-XQ-028 NaN Comparison

From: Michael Kay <mhk@mhk.me.uk>
Date: Fri, 9 Apr 2004 21:01:27 +0100
To: "'Andrew Eisenberg'" <andrew.eisenberg@us.ibm.com>, <public-qt-comments@w3.org>
Message-Id: <20040409200132.13D7EA0E84@frink.w3.org>
```Nice catch, Andrew!

(It should be classified as XPath, though)

Michael Kay

_____

[mailto:public-qt-comments-request@w3.org] On Behalf Of Andrew Eisenberg
Sent: 09 April 2004 18:59
Subject: [XQuery] IBM-XQ-028 NaN Comparison

I believe that "le" and "ge" return the wrong values when NaN values are
provided for either of the two operands.

Consider the following query:

let \$x := 1.0e0
let \$nan := xs:double('NaN')
return
\$x eq \$nan,        (: will return false :)
\$x lt \$nan,        (: will return false :)
\$x gt \$nan,        (: will return false :)
\$x le \$nan,        (: will return true :)
\$x ge \$nan,        (: will return true :)
\$x ne \$nan        (: will return true :)

I believe that "le" and "ge" should return false to be consistent with IEEE
754. They return true because:

1) The definition of op:numeric-less-than and  op:numeric-greater-than in
F&O both contain the following:

"If \$arg1 or \$arg2 is NaN, the function returns false."

2) The Binary Operator table in XQuery, B.2 Operator Mapping, contains the
following:

A ge B        numeric                numeric
fn:not(op:numeric-less-than(A, B))        xs:boolean
A le B        numeric                numeric
fn:not(op:numeric-greater-than(A, B))        xs:boolean

To effect the change I suggest, change the that two rows of the Binary
Operator table to the following:

A ge B        numeric                numeric
op:numeric-greater-than(A, B) or op:numeric-equal(A,B)        xs:boolean
A le B        numeric                numeric
op:numeric-less-than(A, B) or op:numeric-equal(A,B)        xs:boolean

-- Andrew

--------------------
Andrew Eisenberg
IBM
4 Technology Park Drive
Westford, MA  01886

andrew.eisenberg@us.ibm.com
Phone: 978-399-5158    Fax: 978-399-7012
```
Received on Friday, 9 April 2004 16:01:32 UTC

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