Here you can find the source of bigIntegerToUnsignedByteArray(BigInteger a, int len)
public static final byte[] bigIntegerToUnsignedByteArray(BigInteger a, int len) throws NumberFormatException
//package com.java2s; /**/*from ww w.j a va 2s.c om*/ * Hoofprints - An Extensible Testbed for Route-Servers * Copyright (C) 2009 Sebastian Spies * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program 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 General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. * */ import java.math.BigInteger; public class Main { public static final byte[] bigIntegerToUnsignedByteArray(BigInteger a, int len) throws NumberFormatException { byte[] buf = new byte[len]; if (a.bitLength() > len * 8) throw new NumberFormatException("BigInteger doesn't fit into array"); byte[] b = a.toByteArray(); if (b.length == len + 1) if (b[0] == 0) for (int i = 0; i < buf.length; i++) buf[i] = b[i + 1]; else throw new NumberFormatException("Internal Error"); else if (b.length <= len) for (int i = 0; i < b.length; i++) buf[buf.length - 1 - i] = b[b.length - 1 - i]; else throw new NumberFormatException("Internal Error"); return buf; } }