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An OSGi bundle for Saxon-HE
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 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;
import net.sf.saxon.expr.instruct.Choose;
import net.sf.saxon.expr.parser.ExpressionTool;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.expr.parser.Token;
import net.sf.saxon.functions.NotFn;
import net.sf.saxon.functions.SystemFunctionCall;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.BooleanValue;
public class AndExpression extends BooleanExpression{
/**
* Construct a boolean AND expression
* @param p1 the first operand
* @param p2 the second operand
*/
public AndExpression(Expression p1, Expression p2) {
super(p1, Token.AND, p2);
}
/**
* Perform optimisation of an expression and its subexpressions.
*
* 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.
*
* @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 XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
Expression e = super.optimize(visitor, contextItemType);
if (e != this) {
return e;
}
// If the value can be determined from knowledge of one operand, precompute the result
final TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
if (Literal.isConstantBoolean(operand0, false) || Literal.isConstantBoolean(operand1, false)) {
// A and false() => false()
// false() and B => false()
return Literal.makeLiteral(BooleanValue.FALSE);
} else if (Literal.isConstantBoolean(operand0, true)) {
// true() and B => B
return forceToBoolean(operand1, th);
} else if (Literal.isConstantBoolean(operand1, true)) {
// A and true() => A
return forceToBoolean(operand0, th);
}
// Rewrite (A and B) as (if (A) then B else false()). The benefit of this is that when B is a recursive
// function call, it is treated as a tail call (test qxmp290). To avoid disrupting other optimizations
// of "and" expressions (specifically, where clauses in FLWOR expressions), do this ONLY if B is a user
// function call (we can't tell if it's recursive), and it's not in a loop.
if (e == this &&
operand1 instanceof UserFunctionCall &&
th.isSubType(operand1.getItemType(th), BuiltInAtomicType.BOOLEAN) &&
!visitor.isLoopingSubexpression(null)) {
Expression cond = Choose.makeConditional(operand0, operand1, Literal.makeLiteral(BooleanValue.FALSE));
ExpressionTool.copyLocationInfo(this, cond);
return cond;
}
return this;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
/*@NotNull*/
public Expression copy() {
return new AndExpression(operand0.copy(), operand1.copy());
}
/**
* Return the negation of this boolean expression, that is, an expression that returns true
* when this expression returns false, and vice versa
*
* @return the negation of this expression
*/
public Expression negate() {
// Apply de Morgan's laws
// not(A and B) ==> not(A) or not(B)
NotFn not0 = (NotFn) SystemFunctionCall.makeSystemFunction("not", new Expression[]{operand0});
NotFn not1 = (NotFn) SystemFunctionCall.makeSystemFunction("not", new Expression[]{operand1});
return new OrExpression(not0, not1);
}
/**
* Evaluate as a boolean.
*/
public boolean effectiveBooleanValue(XPathContext c) throws XPathException {
return operand0.effectiveBooleanValue(c) && operand1.effectiveBooleanValue(c);
}
}