Java BigInteger to bigIntToSortableBytes(BigInteger bigInt, int bigIntSize, byte[] result, int offset)

Description

Encodes a BigInteger value such that unsigned byte order comparison is consistent with BigInteger#compareTo(BigInteger) .

License

Apache License

Declaration

public static void bigIntToSortableBytes(BigInteger bigInt, int bigIntSize, byte[] result, int offset) 

Method Source Code

//package com.java2s;
/*/*  ww w .j av a2  s .c  o  m*/
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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;
import java.util.Arrays;

public class Main {
    /** 
     * Encodes a BigInteger {@code value} such that unsigned byte order comparison
     * is consistent with {@link BigInteger#compareTo(BigInteger)}. This also sign-extends
     * the value to {@code bigIntSize} bytes if necessary: useful to create a fixed-width size.
     * @see #sortableBytesToBigInt(byte[], int, int)
     */
    public static void bigIntToSortableBytes(BigInteger bigInt, int bigIntSize, byte[] result, int offset) {
        byte[] bigIntBytes = bigInt.toByteArray();
        byte[] fullBigIntBytes;

        if (bigIntBytes.length < bigIntSize) {
            fullBigIntBytes = new byte[bigIntSize];
            System.arraycopy(bigIntBytes, 0, fullBigIntBytes, bigIntSize - bigIntBytes.length, bigIntBytes.length);
            if ((bigIntBytes[0] & 0x80) != 0) {
                // sign extend
                Arrays.fill(fullBigIntBytes, 0, bigIntSize - bigIntBytes.length, (byte) 0xff);
            }
        } else if (bigIntBytes.length == bigIntSize) {
            fullBigIntBytes = bigIntBytes;
        } else {
            throw new IllegalArgumentException(
                    "BigInteger: " + bigInt + " requires more than " + bigIntSize + " bytes storage");
        }
        // Flip the sign bit so negative bigints sort before positive bigints:
        fullBigIntBytes[0] ^= 0x80;

        System.arraycopy(fullBigIntBytes, 0, result, offset, bigIntSize);

        assert sortableBytesToBigInt(result, offset, bigIntSize).equals(bigInt) : "bigInt=" + bigInt + " converted="
                + sortableBytesToBigInt(result, offset, bigIntSize);
    }

    /**
     * Decodes a BigInteger value previously written with {@link #bigIntToSortableBytes}
     * @see #bigIntToSortableBytes(BigInteger, int, byte[], int)
     */
    public static BigInteger sortableBytesToBigInt(byte[] encoded, int offset, int length) {
        byte[] bigIntBytes = new byte[length];
        System.arraycopy(encoded, offset, bigIntBytes, 0, length);
        // Flip the sign bit back to the original
        bigIntBytes[0] ^= 0x80;
        return new BigInteger(bigIntBytes);
    }
}

Related

1. bigIntToArray(BigInteger data)
2. bigIntToHash(BigInteger keyValue)
3. bigIntToHex(BigInteger big)
4. bigIntToIpV6(BigInteger argInt)
5. BigIntToPaddedByteArray(BigInteger bi, int length)
6. biToHex(BigInteger bi)
7. byteConvert32Bytes(BigInteger n)
8. concat(BigInteger left, BigInteger right)
9. convert(BigInteger value, int base, boolean extra)