Java BigInteger to bigIntegerToBytes(BigInteger b, int numBytes)

Description

The regular java.math.BigInteger#toByteArray() method isn't quite what we often need: it appends a leading zero to indicate that the number is positive and may need padding.

License

Apache License

Parameter

Parameter	Description
b	the integer to format into a byte array
numBytes	the desired size of the resulting byte array

Return

numBytes byte long array.

Declaration

public static byte[] bigIntegerToBytes(BigInteger b, int numBytes)

Method Source Code

//package com.java2s;
/*// w  w w  .j a v a  2s . c o  m
 * Copyright 2011 Google Inc.
 * Copyright 2014 Andreas Schildbach
 *
 * Licensed 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.
 */

import java.math.BigInteger;

public class Main {
    /**
     * The regular {@link java.math.BigInteger#toByteArray()} method isn't quite what we often need: it appends a
     * leading zero to indicate that the number is positive and may need padding.
     *
     * @param b the integer to format into a byte array
     * @param numBytes the desired size of the resulting byte array
     * @return numBytes byte long array.
     */
    public static byte[] bigIntegerToBytes(BigInteger b, int numBytes) {
        byte[] bytes = new byte[numBytes];
        byte[] biBytes = b.toByteArray();
        int start = (biBytes.length == numBytes + 1) ? 1 : 0;
        int length = Math.min(biBytes.length, numBytes);
        System.arraycopy(biBytes, start, bytes, numBytes - length, length);
        return bytes;
    }
}