At 2006-05-15 11:19 +0200, David Landwehr wrote:
Reading XPath 1.0 it states that a predicate evaluating to a number
will return true if equal to the proximity position of the current
node. I was wondering if there is a reason the evaluated number
isn't rounded by the XPath engine? Because XPath is based on IEEE
754 the result of an evaluation might be inaccurate on the last
digit which will cause a predicate to return false where it should
return true. I'm just asking this out of curiosity and accepts that
an author has to call the round function if she uses arithmetic
which can give inaccurate results.
As the typical use is merely ordinal position in a node set I've
never had to worry about this in a predicate ... but I did have to
think about position() and rounding in a standalone <xsl:if> when
doing a two-column display in XSL-FO and I wanted to introduce a
column break in a standalone block ... I might have wanted to use
floor() instead of round() in the following:
<xsl:if test="position()=round(last() div 2)">
<block break-before="column"/>
</xsl:if>
... but I cannot readily extrapolate that into an XPath predicate.
I think you summarized correctly that if the author is doing things
that might give inaccurate results they should do it explicitly ...
as in my case they might want to make the decision between floor()
and ceiling() but in a predicate rather than just round(), so I don't
believe it makes sense to just implement round() by default.
I hope this helps.
. . . . . . . . . Ken
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