Return the value of BigInteger as a byte array. - Java java.math

Java examples for java.math:BigInteger

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Description

Return the value of BigInteger as a byte array.

Demo Code


//package com.java2s;
import java.math.BigInteger;

public class Main {
    public static void main(String[] argv) throws Exception {
        BigInteger value = new BigInteger("1234");
        System.out.println(java.util.Arrays
                .toString(toMinimalByteArray(value)));
    }/*  w w w  . j av  a2  s .c  o m*/

    /**
     * Return the value of <tt>big</tt> as a byte array. Although BigInteger has
     * such a method, it uses an extra bit to indicate the sign of the number.
     * For elliptic curve cryptography, the numbers usually are positive. Thus,
     * this helper method returns a byte array of minimal length, ignoring the
     * sign of the number.
     * 
     * @param value
     *            the <tt>BigInteger</tt> value to be converted to a byte array
     * @return the value <tt>big</tt> as byte array
     */
    public static byte[] toMinimalByteArray(BigInteger value) {
        byte[] valBytes = value.toByteArray();
        if ((valBytes.length == 1) || (value.bitLength() & 0x07) != 0) {
            return valBytes;
        }
        byte[] result = new byte[value.bitLength() >> 3];
        System.arraycopy(valBytes, 1, result, 0, result.length);
        return result;
    }
}

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