Java BigInteger from Stream readBigInteger(InputStream input)

Description

Read the signed arbitrary sized BigInteger BigInteger in vint format

License

Apache License

Parameter

Parameter	Description
input	the stream to read from

Exception

Parameter	Description
IOException	an exception

Return

the read BigInteger

Declaration

static BigInteger readBigInteger(InputStream input) throws IOException 

Method Source Code

//package com.java2s;
/**// w  ww. j a  v a2 s .  com
 * 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.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import java.math.BigInteger;

public class Main {
    /**
     * Read the signed arbitrary sized BigInteger BigInteger in vint format
     * @param input the stream to read from
     * @return the read BigInteger
     * @throws IOException
     */
    static BigInteger readBigInteger(InputStream input) throws IOException {
        BigInteger result = BigInteger.ZERO;
        long work = 0;
        int offset = 0;
        long b;
        do {
            b = input.read();
            if (b == -1) {
                throw new EOFException("Reading BigInteger past EOF from " + input);
            }
            work |= (0x7f & b) << (offset % 63);
            offset += 7;
            // if we've read 63 bits, roll them into the result
            if (offset == 63) {
                result = BigInteger.valueOf(work);
                work = 0;
            } else if (offset % 63 == 0) {
                result = result.or(BigInteger.valueOf(work).shiftLeft(offset - 63));
                work = 0;
            }
        } while (b >= 0x80);
        if (work != 0) {
            result = result.or(BigInteger.valueOf(work).shiftLeft((offset / 63) * 63));
        }
        // convert back to a signed number
        boolean isNegative = result.testBit(0);
        if (isNegative) {
            result = result.add(BigInteger.ONE);
            result = result.negate();
        }
        result = result.shiftRight(1);
        return result;
    }
}

Related

1. readBigInteger(ByteArrayInputStream bais)
2. readBigInteger(DataInputStream dis)
3. readBigInteger(int n, DataInput dis)
4. readLineAsBigInteger(BufferedReader br)
5. readLuposBigInteger(final int numberOfBits, final InputStream is)