doubleparser.java

一个开源的JAVA虚拟机

/*
    libaegisvm - The Aegis Virtual Machine for executing Java bytecode
    Copyright (C) 2001-2002  Philip W. L. Fong

    This library 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 2.1 of the License, or (at your option) any later version.

    This library 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 this library; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/

//
// Taken from Kore 0.0.7
//

package aegis;

public final class DoubleParser {
    private char[] chars;
    private int length;
    private int index;

    private int parseUnsignedInt() throws NumberFormatException	{
	if (index >= length)
	    throw new NumberFormatException();

	int start = index;
	int value = 0;

	for ( ; index < length; index++) {
	    int d = Character.digit(chars[index], 10);
	    if (d < 0)
		break;
	    value *= 10;
	    value += d;
	}

	if (index == start)
	    throw new NumberFormatException();

	return value;
    }

    private int parseSignedInt() throws NumberFormatException {
	if (index >= length)
	    throw new NumberFormatException();

	char sign = '+';

	switch (chars[index]) {
	case '-':
	    sign = '-';
	    index++;
	    break;
	case '+':
	    sign = '+';
	    index++;
	    break;
	}

	int value = parseUnsignedInt();

	return (sign == '-') ? -value : value;
    }

    private double parseIntegerPart() throws NumberFormatException {
	if (index >= length)
	    throw new NumberFormatException();
	double value = 0.0;
	for ( ; index < length; index++) {
	    int d = Character.digit(chars[index], 10);
	    if (d < 0)
		break;
	    value *= 10;
	    value += d;
	}

	return value;
    }
    private double parseFractionalPart(boolean nonEmpty)
	throws NumberFormatException {
	if (index >= length)
	    throw new NumberFormatException();

	int start = index;
	double value = 0.0;
	int c = 0;

	for ( ; index < length; index++) {
	    int d = Character.digit(chars[index], 10);
	    if (d < 0)
		break;
	    c++;
	    if (c < negexp.length)
		value += negexp[c] * d;
	}

	if (nonEmpty && (index == start))
	    throw new NumberFormatException();
	
	return value;
    }

    private static final double negexp[] = {
	1e-0, 1e-1, 1e-2, 1e-3, 1e-4,
	1e-5, 1e-6, 1e-7, 1e-8, 1e-9,
	1e-10, 1e-11, 1e-12, 1e-13, 1e-14,
	1e-15, 1e-16, 1e-17, 1e-18, 1e-19,
	1e-20, 1e-21, 1e-22, 1e-23, 1e-24,
	1e-25, 1e-26, 1e-27, 1e-28, 1e-29
    };
    private double parseExponent(double value) throws NumberFormatException {
	if (index >= chars.length)
	    return value;

	switch (chars[index]) {
	case 'e':
	case 'E':
	    index++;
	    break;
	default:
	    throw new NumberFormatException();
	}

	int exponent = parseSignedInt();

	if (index < chars.length)
	    throw new NumberFormatException();

	if (exponent >= 0) {
	    for (int i = 0; i < exponent; i++)
		value *= 10.0;
	    return value;
	} else if (exponent > -negexp.length) {
	    return value * negexp[-exponent];
	} else {
	    for (int i = 0; i > exponent; i--)
		value /= 10.0;
	    return value;
	}
    }

    public double parse() throws NumberFormatException {
	if (index >= chars.length)
	    throw new NumberFormatException();

	char sign = '+';

	switch (chars[index]) {
	case '-':
	    sign = '-';
	    index++;
	    break;

	case '+':
	    sign = '+';
	    index++;
	    break;
	}

	if (index >= chars.length)
	    throw new NumberFormatException();

	double value;

	if (chars[index] == '.') {
	    index++;
	    value = parseFractionalPart(true);
	    value = parseExponent(value);
	} else {

	    value = parseIntegerPart();

	    if (index >= chars.length)
		throw new NumberFormatException();
	    if (chars[index] != '.') {
		throw new NumberFormatException();
	    }

	    index++;

	    value += parseFractionalPart(false);
	    value = parseExponent(value);
	}

	return (sign == '-') ? -value : value;
    }

    public DoubleParser(String s) {
	chars = s.toCharArray();
	length = chars.length;
	index = 0;
    }

    public static double parseDouble(String s) throws NumberFormatException {
	DoubleParser p = new DoubleParser(s);
	return p.parse();
    }
}