package net.sf.saxon.functions;
import net.sf.saxon.expr.*;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.om.EmptyIterator;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.AtomicValue;
import net.sf.saxon.value.NumericValue;
import net.sf.saxon.value.Int64Value;
import net.sf.saxon.value.EmptySequence;
/**
* Implements the XPath 2.0 subsequence() function
*/
public class Subsequence extends SystemFunction {
/**
* Determine the data type of the items in the sequence
* @return the type of the argument
* @param th the type hierarchy cache
*/
public ItemType getItemType(TypeHierarchy th) {
return argument[0].getItemType(th);
}
/**
* Get the static properties of this expression (other than its type). The result is
* bit-significant. These properties are used for optimizations. In general, if
* property bit is set, it is true, but if it is unset, the value is unknown.
*/
public int computeSpecialProperties() {
return argument[0].getSpecialProperties();
}
/**
* Determine the cardinality of the function.
*/
public int computeCardinality() {
if (getNumberOfArguments() == 3 && Literal.isConstantOne(argument[2])) {
return StaticProperty.ALLOWS_ZERO_OR_ONE;
}
return argument[0].getCardinality() | StaticProperty.ALLOWS_ZERO;
}
/**
* Perform optimisation of an expression and its subexpressions.
* <p/>
* <p>This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable, and after all type checking has been done.</p>
*
* @param visitor an expression visitor
* @param contextItemType the static type of "." at the point where this expression is invoked.
* The parameter is set to null if it is known statically that the context item will be undefined.
* If the type of the context item is not known statically, the argument is set to
* {@link net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws net.sf.saxon.trans.XPathException
* if an error is discovered during this phase
* (typically a type error)
*/
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
Expression e = super.optimize(visitor, contextItemType);
if (e != this) {
return e;
}
if (getNumberOfArguments() == 2 && Literal.isAtomic(argument[1])) {
NumericValue start = (NumericValue)((Literal)argument[1]).getValue();
start = start.round();
long intstart = start.longValue();
if (intstart > Integer.MAX_VALUE) {
return new Literal(EmptySequence.getInstance());
}
return new TailExpression(argument[0], (int)intstart);
}
return this;
}
/**
* Evaluate the function to return an iteration of selected nodes.
*/
public SequenceIterator iterate(XPathContext context) throws XPathException {
SequenceIterator seq = argument[0].iterate(context);
AtomicValue startVal0 = (AtomicValue)argument[1].evaluateItem(context);
NumericValue startVal = (NumericValue)startVal0;
if (argument.length == 2) {
long lstart;
if (startVal instanceof Int64Value) {
lstart = startVal.longValue();
if (lstart <= 1) {
return seq;
}
} else {
startVal = startVal.round();
if (startVal.compareTo(Int64Value.PLUS_ONE) <= 0) {
return seq;
} else if (startVal.compareTo(Int64Value.MAX_LONG) > 0) {
return EmptyIterator.getInstance();
} else if (startVal.isNaN()) {
return EmptyIterator.getInstance();
} else {
lstart = startVal.longValue();
}
}
if (lstart > Integer.MAX_VALUE) {
// we don't allow sequences longer than an this
return EmptyIterator.getInstance();
}
return TailIterator.make(seq, (int)lstart);
} else {
// There are three arguments
AtomicValue lengthVal0 = (AtomicValue)argument[2].evaluateItem(context);
NumericValue lengthVal = (NumericValue)lengthVal0;
if (startVal instanceof Int64Value && lengthVal instanceof Int64Value) {
long lstart = startVal.longValue();
if (lstart > Integer.MAX_VALUE) {
return EmptyIterator.getInstance();
}
long llength = lengthVal.longValue();
if (llength > Integer.MAX_VALUE) {
llength = Integer.MAX_VALUE;
}
if (llength < 1) {
return EmptyIterator.getInstance();
}
long lend = lstart + llength - 1;
if (lend < 1) {
return EmptyIterator.getInstance();
}
int start = (lstart < 1 ? 1 : (int)lstart);
return SubsequenceIterator.make(seq, start, (int)lend);
} else {
if (startVal.isNaN()) {
return EmptyIterator.getInstance();
}
if (startVal.compareTo(Int64Value.MAX_LONG) > 0) {
return EmptyIterator.getInstance();
}
startVal = startVal.round();
if (lengthVal.isNaN()) {
return EmptyIterator.getInstance();
}
lengthVal = lengthVal.round();
if (lengthVal.compareTo(Int64Value.ZERO) <= 0) {
return EmptyIterator.getInstance();
}
NumericValue rend = (NumericValue)ArithmeticExpression.compute(
startVal, Calculator.PLUS, lengthVal, context);
rend = (NumericValue)ArithmeticExpression.compute(
rend, Calculator.MINUS, Int64Value.PLUS_ONE, context);
if (rend.compareTo(Int64Value.ZERO) <= 0) {
return EmptyIterator.getInstance();
}
long lstart;
if (startVal.compareTo(Int64Value.PLUS_ONE) <= 0) {
lstart = 1;
} else {
lstart = startVal.longValue();
}
if (lstart > Integer.MAX_VALUE) {
return EmptyIterator.getInstance();
}
long lend;
if (rend.compareTo(Int64Value.MAX_LONG) >= 0) {
lend = Integer.MAX_VALUE;
} else {
lend = rend.longValue();
}
return SubsequenceIterator.make(seq, (int)lstart, (int)lend);
}
}
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//