RoundFunction.java

/*
 * @(#)RoundFunction.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
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 * This software is provided "AS IS," without a warranty of any kind. ALL
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package com.sun.xacml.cond;

import java.util.HashSet;
import java.util.List;
import java.util.Set;

import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.attr.AttributeValue;
import com.sun.xacml.attr.DoubleAttribute;

/**
 * A class that implements the round function. It takes one double operand, rounds that value to an
 * integer and returns that integer. If the operand is indeterminate, an indeterminate result is
 * returned.
 * 
 * @since 1.0
 * @author Steve Hanna
 * @author Seth Proctor
 * 
 *         Adding generic type support by Christian Mueller (geotools)
 */
public class RoundFunction extends FunctionBase {

    /**
     * Standard identifier for the round function.
     */
    public static final String NAME_ROUND = FUNCTION_NS + "round";

    /**
     * Creates a new <code>RoundFunction</code> object.
     * 
     * @param functionName
     *            the standard XACML name of the function to be handled by this object, including
     *            the full namespace
     * 
     * @throws IllegalArgumentException
     *             if the function is unknown
     */
    public RoundFunction(String functionName) {
        super(NAME_ROUND, 0, DoubleAttribute.identifier, false, 1, DoubleAttribute.identifier,
                false);

        if (!functionName.equals(NAME_ROUND))
            throw new IllegalArgumentException("unknown round function: " + functionName);
    }

    /**
     * Returns a <code>Set</code> containing all the function identifiers supported by this class.
     * 
     * @return a <code>Set</code> of <code>String</code>s
     */
    public static Set<String> getSupportedIdentifiers() {
        Set<String> set = new HashSet<String>();

        set.add(NAME_ROUND);

        return set;
    }

    /**
     * Evaluate the function, using the specified parameters.
     * 
     * @param inputs
     *            a <code>List</code> of <code>Evaluatable</code> objects representing the arguments
     *            passed to the function
     * @param context
     *            an <code>EvaluationCtx</code> so that the <code>Evaluatable</code> objects can be
     *            evaluated
     * @return an <code>EvaluationResult</code> representing the function's result
     */
    public EvaluationResult evaluate(List<? extends Expression> inputs, EvaluationCtx context) {

        // Evaluate the arguments
        AttributeValue[] argValues = new AttributeValue[inputs.size()];
        EvaluationResult result = evalArgs(inputs, context, argValues);
        if (result != null)
            return result;

        // Now that we have real values, perform the round operation
        double arg = ((DoubleAttribute) argValues[0]).getValue();
        double roundValue = Math.round(arg);

        // Make it round half even, not round nearest
        double lower = Math.floor(arg);
        double higher = lower + 1;

        if ((arg - lower) == (higher - arg)) {
            if ((lower % 2) == 0)
                roundValue = lower;
            else
                roundValue = higher;
        }

        return new EvaluationResult(new DoubleAttribute(roundValue));
    }
}