Java BigInteger Calculate decodeToBigInteger(String input)

Description

decode To Big Integer

License

Apache License

Declaration

public static BigInteger decodeToBigInteger(String input)

Method Source Code

//package com.java2s;
/*// w w  w  .  ja v a  2s .  c o m
 * Copyright 2014 http://Bither.net
 *
 * 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 {
    private static final int[] INDEXES = new int[128];

    public static BigInteger decodeToBigInteger(String input) {
        return new BigInteger(1, decode(input));
    }

    public static byte[] decode(String input) {

        if (input.length() == 0) {
            return new byte[0];
        }
        // Get rid of any UTF-8 BOM marker. Those should not be present, but might have slipped in nonetheless,
        // since Java does not automatically discard them when reading a stream. Only remove it, if at the beginning
        // of the string. Otherwise, something is probably seriously wrong.
        if (input.charAt(0) == '\uFEFF')
            input = input.substring(1);

        byte[] input58 = new byte[input.length()];
        // Transform the String to a base58 byte sequence
        for (int i = 0; i < input.length(); ++i) {
            char c = input.charAt(i);

            int digit58 = -1;
            if (c >= 0 && c < 128) {
                digit58 = INDEXES[c];
            }
            if (digit58 < 0) {
                return null;
            }

            input58[i] = (byte) digit58;
        }
        // Count leading zeroes
        int zeroCount = 0;
        while (zeroCount < input58.length && input58[zeroCount] == 0) {
            ++zeroCount;
        }
        // The encoding
        byte[] temp = new byte[input.length()];
        int j = temp.length;

        int startAt = zeroCount;
        while (startAt < input58.length) {
            byte mod = divmod256(input58, startAt);
            if (input58[startAt] == 0) {
                ++startAt;
            }

            temp[--j] = mod;
        }
        // Do no add extra leading zeroes, move j to first non null byte.
        while (j < temp.length && temp[j] == 0) {
            ++j;
        }

        return copyOfRange(temp, j - zeroCount, temp.length);
    }

    private static byte divmod256(byte[] number58, int startAt) {
        int remainder = 0;
        for (int i = startAt; i < number58.length; i++) {
            int digit58 = (int) number58[i] & 0xFF;
            int temp = remainder * 58 + digit58;

            number58[i] = (byte) (temp / 256);

            remainder = temp % 256;
        }

        return (byte) remainder;
    }

    private static byte[] copyOfRange(byte[] source, int from, int to) {
        byte[] range = new byte[to - from];
        System.arraycopy(source, from, range, 0, range.length);

        return range;
    }
}

Java BigInteger Calculate decodeToBigInteger(String input)

Description

License

Declaration

Method Source Code

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