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Google App Engine compliant variation of FreeMarker. FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package freemarker.template.utility;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 */
public class OptimizerUtil {
    private static final BigInteger INTEGER_MIN = new BigInteger(Integer.toString(Integer.MIN_VALUE));
    private static final BigInteger INTEGER_MAX = new BigInteger(Integer.toString(Integer.MAX_VALUE));
    private static final BigInteger LONG_MIN = new BigInteger(Long.toString(Long.MIN_VALUE));
    private static final BigInteger LONG_MAX = new BigInteger(Long.toString(Long.MAX_VALUE));

    private OptimizerUtil() {
    }
    
    public static List optimizeListStorage(List list) {
        switch(list.size())
        {
            case 0:
            {
                return Collections.EMPTY_LIST;
            }
            case 1:
            {
                return Collections.singletonList(list.get(0));
            }
            default:
            {
                if (list instanceof ArrayList) {
                    ((ArrayList) list).trimToSize();
                }
                return list;
            }
        }
    }
    
    /**
     * This is needed to reverse the extreme conversions in arithmetic 
     * operations so that numbers can be meaningfully used with models that
     * don't know what to do with a BigDecimal. Of course, this will make
     * impossible for these models (i.e. Jython) to receive a BigDecimal even if 
     * it was originally placed as such in the data model. However, since 
     * arithmetic operations aggressively erase the information regarding the 
     * original number type, we have no other choice to ensure expected operation
     * in majority of cases.
     */
    public static Number optimizeNumberRepresentation(Number number) {
        if (number instanceof BigDecimal) {
            BigDecimal bd = (BigDecimal) number;
            if (bd.scale() == 0) {
                // BigDecimal -> BigInteger
                number = bd.unscaledValue();
            } else {
                double d = bd.doubleValue();
                if (d != Double.POSITIVE_INFINITY && d != Double.NEGATIVE_INFINITY) {
                    // BigDecimal -> Double
                    return Double.valueOf(d);
                }
            }
        }
        if (number instanceof BigInteger) {
            BigInteger bi = (BigInteger) number;
            if (bi.compareTo(INTEGER_MAX) <= 0 && bi.compareTo(INTEGER_MIN) >= 0) {
                // BigInteger -> Integer
                return Integer.valueOf(bi.intValue());
            }
            if (bi.compareTo(LONG_MAX) <= 0 && bi.compareTo(LONG_MIN) >= 0) {
                // BigInteger -> Long
                return Long.valueOf(bi.longValue());
            }
        }
        return number;
    }
}