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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr.sort;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.lib.StringCollator;
import net.sf.saxon.value.AtomicValue;
import net.sf.saxon.value.StringValue;
/**
* An AtomicComparer used for comparing strings, untypedAtomic values, and URIs using the Unicode codepoint
* collation.
* A CodepointCollatingComparer is used when it is known in advance that both operands will be of these
* types, and when the collation is the unicode codepoint collation.
* This enables all conversions and promotions to be bypassed: the string values of both operands
* are simply extracted and passed to the collator for comparison.
* The difference between using this class and using the underlying CodepointCollator directly is that
* the compare() method in this class expects two instances of AtomicValue as its operands, whereas the
* underlying class expects two instances of java.lang.String. This class makes use of the extra information
* held in the wrapping StringValue object, specifically, the knowledge of whether the string contains
* surrogate pairs.
*
*/
public class CodepointCollatingComparer implements AtomicComparer {
private static final CodepointCollator collator = CodepointCollator.getInstance();
private static final CodepointCollatingComparer THE_INSTANCE = new CodepointCollatingComparer();
/**
* Get the singular instance of this class
*
* @return the singleton instance
*/
public static CodepointCollatingComparer getInstance() {
return THE_INSTANCE;
}
private CodepointCollatingComparer() {
}
@Override
public StringCollator getCollator() {
return collator;
}
/**
* Supply the dynamic context in case this is needed for the comparison
*
* @param context the dynamic evaluation context
* @return either the original AtomicComparer, or a new AtomicComparer in which the context
* is known. The original AtomicComparer is not modified
*/
@Override
public AtomicComparer provideContext(XPathContext context) {
return this;
}
/**
* Compare two AtomicValue objects according to the rules for their data type. UntypedAtomic
* values are compared as if they were strings; if different semantics are wanted, the conversion
* must be done by the caller.
*
* @param a the first object to be compared. This must be either be an instance
* of AtomicValue, or null to represent an empty sequence. Empty collates before non-empty.
* @param b the second object to be compared. This must be either be an instance
* of AtomicValue, or null to represent an empty sequence.
* @return <0 if a<b, 0 if a=b, >0 if a>b
* @throws ClassCastException if the objects are not comparable
*/
@Override
public int compareAtomicValues(/*@Nullable*/ AtomicValue a, AtomicValue b) {
if (a == null) {
return (b == null ? 0 : -1);
} else if (b == null) {
return +1;
}
StringValue as = (StringValue) a;
StringValue bs = (StringValue) b;
//if (as.containsSurrogatePairs() || bs.containsSurrogatePairs()) {
return collator.compareStrings(as.getUnicodeStringValue(), bs.getUnicodeStringValue());
//} else {
// optimize to use UTF-16 binary comparison
// return as.getStringValue().compareTo(bs.getStringValue());
//}
}
/**
* Compare two AtomicValue objects for equality. The values must be instances of xs:string or a type
* derived from xs:string. The method will also handle xs:untypedAtomic and xs:anyURI values.
*
* @param a the first object to be compared.
* @param b the second object to be compared.
* @return true if the values are equal, false if not
* @throws ClassCastException if either value is not xs:string or a subtype
*/
@Override
public boolean comparesEqual(AtomicValue a, AtomicValue b) {
return ((StringValue)a).equals((StringValue)b);
}
/**
* Create a string representation of this AtomicComparer that can be saved in a compiled
* package and used to reconstitute the AtomicComparer when the package is reloaded
*
* @return a string representation of the AtomicComparer
*/
@Override
public String save() {
return "CCC";
}
}