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Jiffle is a raster algebra language that can be used to create new images from logical and mathematical expressions involving source images and user defined variables. It is intended to let users concentrate on algorithms rather than tedious boiler-plate code.

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/*
 * Copyright 2011 Michael Bedward
 * 
 * This file is part of jai-tools.
 *
 * jai-tools is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the 
 * License, or (at your option) any later version.
 *
 * jai-tools is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public 
 * License along with jai-tools.  If not, see .
 * 
 */

package jaitools.jiffle.parser;

import java.util.Map;

import jaitools.CollectionFactory;

/**
 * A lookup for named constants used by the Jiffle compiler.
 * 
 * The following constants are recognized:
 * 
 * M_E     The base of natural logarithms (e)
 * M_PI    Pi
 * M_PI_2  Pi / 2
 * M_PI_4  Pi / 4
 * M_SQRT2 Squre root of 2
 * 
 * In addition, any of the following can be used for {@code Double.NaN}
 *  * M_NaN
 * M_NAN
 * NaN
 * NAN
 * 
 * 
 * @author Michael Bedward
 * @since 1.1
 * @version $Id: ConstantLookup.java 1383 2011-02-10 11:22:29Z michael.bedward $
 */
public class ConstantLookup {

    private static final Map constants;
    static {
        constants = CollectionFactory.map();
        
        constants.put("M_E", Math.E);
        constants.put("M_PI", Math.PI);
        constants.put("M_PI_2", Math.PI / 2);
        constants.put("M_PI_4", Math.PI / 4);
        constants.put("M_SQRT2", Math.sqrt(2.0));
        
        // be generous with NaN names
        constants.put("M_NaN", Double.NaN);
        constants.put("M_NAN", Double.NaN);
        constants.put("NaN", Double.NaN);
        constants.put("NAN", Double.NaN);
    }
    
    /**
     * Checks if a constant is recognized by Jiffle.
     * 
     * @param name the name
     * 
     * @return {@code true} if the constant is recognized;
     *         {@code false} otherwise
     */
    public static boolean isDefined(String name) {
        return constants.containsKey(name);
    }

    /**
     * Gets the value of a named constant.
     * 
     * @param name the constant
     * 
     * @return the value
     * 
     * @throws IllegalArgumentException if {@code name} is not recognized
     */
    public static double getValue(String name) {
        Double value = constants.get(name);
        if (value == null) {
            throw new IllegalArgumentException("Unknown constant: " + name);
        }
        return value;
    }
 
}