Java Double to doubleToRational(double number)

Description

double To Rational

License

Open Source License

Declaration

public static long[] doubleToRational(double number) 

Method Source Code

//package com.java2s;
/**// ww w .j  a  va2  s . c  o m
 * Copyright (c) 2014-2015 by Wen Yu.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Any modifications to this file must keep this entire header intact.
 */

public class Main {
    public static long[] doubleToRational(double number) {
        // Code below doesn't work for 0 and NaN - just check before
        if ((number == 0.0d) || Double.isNaN(number)) {
            throw new IllegalArgumentException(number + " cannot be represented as a rational number");
        }

        long bits = Double.doubleToLongBits(number);

        long sign = bits >>> 63;
        long exponent = ((bits >>> 52) ^ (sign << 11)) - 1023;
        long fraction = bits << 12; // bits are "reversed" but that's not a problem

        long a = 1L;
        long b = 1L;

        for (int i = 63; i >= 12; i--) {
            a = a * 2 + ((fraction >>> i) & 1);
            b *= 2;
        }

        if (exponent > 0)
            a *= 1 << exponent;
        else
            b *= 1 << -exponent;

        if (sign == 1)
            a *= -1;

        return new long[] { a, b };
    }
}

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