Bug #3167: Problems with QName hash-codes in trieWithCollation() - SaxonJS - Saxonica Developer Community

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Bug #3167

closed

Problems with QName hash-codes in trieWithCollation()

Added by John Lumley about 7 years ago. Updated over 6 years ago.

Status:

Closed

Priority:

Normal

Assignee:

Debbie Lockett

Category:

Sprint/Milestone:

Start date:

2017-03-14

Due date:

% Done:

100%

Estimated time:

Applies to JS Branch:

Trunk

Fix Committed on JS Branch:

Trunk

Fixed in JS Release:

Saxon-JS 1.0.1

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Description

In cases where the key for a map entry is a QName@, rather than 'string-like', a hash function wasn't being assigned. This requires some careful alterations to the logic in @Compare.js#trieWithCollation()

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Updated by Michael Kay almost 7 years ago

There are two further problems here:

(a) for non-string keys, we are treating keys as equal if their hash codes are equal.

(b) For QNames, we have a very poor hash function, specifically:

return this.uri.substring(this.uri.length - 3) + ":" + this.local.substring(0, 3);

A better one would be

return this.uri.substring(this.uri.length - 3) + ":" + new XdmString(this.local).hashCode()

Test case: try grouping elements by node-name() where there are elements whose names don't vary in the first four characters.

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Updated by Michael Kay almost 7 years ago

Assignee changed from Michael Kay to Debbie Lockett

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Updated by Debbie Lockett almost 7 years ago

Found in version deleted (~~1.0.0~~)

trieWithCollation is new development code since the release of Saxon-JS 1.0.0.

It may be worth testing whether the same bug arises when grouping by element name using Saxon-JS 1.0.0. Or whether it is just now broken in the development version. (For now I'm declassifying this bug from being 'found in version Saxon-JS 1.0.0'.)

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Updated by Debbie Lockett almost 7 years ago

Status changed from New to Resolved

XSLT 3.0 test for-each-group-082 added.

Saxon-JS code fixes:

Atomic.XdmQName.hashCode updated as suggested in (b).
New method matchKey() added to all classes for primitive types. matchKey() returns a string representation of the value, such that

![]((a.equals(b)) implies (matchKey(a) ) i.e. the matchKey strings are always different for different values. (Note that this condition is not always true for hash codes, so they are not always suitable.)

matchKey() can then be used by matchFn() in Compare.trieWithCollation.

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