/*

   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 org.apache.batik.parser;

import java.io.IOException;

/**
 * This class represents a parser with support for numbers.
 *
 * @author <a href="mailto:stephane@hillion.org">Stephane Hillion</a>
 * @version $Id$
 */
public abstract class NumberParser extends AbstractParser {

    /**
     * Parses the content of the buffer and converts it to a float.
     */
    protected float parseFloat() throws ParseException, IOException {
        int     mant     = 0;
        int     mantDig  = 0;
        boolean mantPos  = true;
        boolean mantRead = false;

        int     exp      = 0;
        int     expDig   = 0;
        int     expAdj   = 0;
        boolean expPos   = true;

        switch (current) {
        case '-':
            mantPos = false;
            // fallthrough
        case '+':
            current = reader.read();
        }

        m1: switch (current) {
        default:
            reportUnexpectedCharacterError( current );
            return 0.0f;

        case '.':
            break;

        case '0':
            mantRead = true;
            l: for (;;) {
                current = reader.read();
                switch (current) {
                case '1': case '2': case '3': case '4':
                case '5': case '6': case '7': case '8': case '9':
                    break l;
                case '.': case 'e': case 'E':
                    break m1;
                default:
                    return 0.0f;
                case '0':
                }
            }

        case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
            mantRead = true;
            l: for (;;) {
                if (mantDig < 9) {
                    mantDig++;
                    mant = mant * 10 + (current - '0');
                } else {
                    expAdj++;
                }
                current = reader.read();
                switch (current) {
                default:
                    break l;
                case '0': case '1': case '2': case '3': case '4':
                case '5': case '6': case '7': case '8': case '9':
                }
            }
        }

        if (current == '.') {
            current = reader.read();
            m2: switch (current) {
            default:
            case 'e': case 'E':
                if (!mantRead) {
                    reportUnexpectedCharacterError( current );
                    return 0.0f;
                }
                break;

            case '0':
                if (mantDig == 0) {
                    l: for (;;) {
                        current = reader.read();
                        expAdj--;
                        switch (current) {
                        case '1': case '2': case '3': case '4':
                        case '5': case '6': case '7': case '8': case '9':
                            break l;
                        default:
                            if (!mantRead) {
                                return 0.0f;
                            }
                            break m2;
                        case '0':
                        }
                    }
                }
            case '1': case '2': case '3': case '4':
            case '5': case '6': case '7': case '8': case '9':
                l: for (;;) {
                    if (mantDig < 9) {
                        mantDig++;
                        mant = mant * 10 + (current - '0');
                        expAdj--;
                    }
                    current = reader.read();
                    switch (current) {
                    default:
                        break l;
                    case '0': case '1': case '2': case '3': case '4':
                    case '5': case '6': case '7': case '8': case '9':
                    }
                }
            }
        }

        switch (current) {
        case 'e': case 'E':
            current = reader.read();
            switch (current) {
            default:
                reportUnexpectedCharacterError( current );
                return 0f;
            case '-':
                expPos = false;
            case '+':
                current = reader.read();
                switch (current) {
                default:
                    reportUnexpectedCharacterError( current );
                    return 0f;
                case '0': case '1': case '2': case '3': case '4':
                case '5': case '6': case '7': case '8': case '9':
                }
            case '0': case '1': case '2': case '3': case '4':
            case '5': case '6': case '7': case '8': case '9':
            }

            en: switch (current) {
            case '0':
                l: for (;;) {
                    current = reader.read();
                    switch (current) {
                    case '1': case '2': case '3': case '4':
                    case '5': case '6': case '7': case '8': case '9':
                        break l;
                    default:
                        break en;
                    case '0':
                    }
                }

            case '1': case '2': case '3': case '4':
            case '5': case '6': case '7': case '8': case '9':
                l: for (;;) {
                    if (expDig < 3) {
                        expDig++;
                        exp = exp * 10 + (current - '0');
                    }
                    current = reader.read();
                    switch (current) {
                    default:
                        break l;
                    case '0': case '1': case '2': case '3': case '4':
                    case '5': case '6': case '7': case '8': case '9':
                    }
                }
            }
        default:
        }

        if (!expPos) {
            exp = -exp;
        }
        exp += expAdj;
        if (!mantPos) {
            mant = -mant;
        }

        return buildFloat(mant, exp);
    }

    /**
     * Computes a float from mantissa and exponent.
     */
    public static float buildFloat(int mant, int exp) {
        if (exp < -125 || mant == 0) {
            return 0.0f;
        }

        if (exp >=  128) {
            return (mant > 0)
                ? Float.POSITIVE_INFINITY
                : Float.NEGATIVE_INFINITY;
        }

        if (exp == 0) {
            return mant;
        }

        if (mant >= (1 << 26)) {
            mant++;  // round up trailing bits if they will be dropped.
        }

        return (float) ((exp > 0) ? mant * pow10[exp] : mant / pow10[-exp]);
    }

    /**
     * Array of powers of ten. Using double instead of float gives a tiny bit more precision.
     */
    private static final double[] pow10 = new double[128];

    static {
        for (int i = 0; i < pow10.length; i++) {
            pow10[i] = Math.pow(10, i);
        }
    }
}
