net.siisise.io.BASE58 Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of softlib Show documentation
Java simple API Packet io, base64, etc...
There is a newer version: 1.1.15
/*
 * Copyright 2023 okome.
 *
 * 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.
 */
package net.siisise.io;

import java.math.BigInteger;
import java.util.Arrays;

/**
 * Base58を可変長にしたもの.
 * その他サイズでもよい。
 */
public class BASE58 implements TextEncode {

    static final String BITCOIN = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
    static final String RIPPLE  = "rpshnaf39wBUDNEGHJKLM4PQRST7VWXYZ2bcdeCg65jkm8oFqi1tuvAxyz";

    private char[] enc;
    private short[] rbit;
    private BigInteger FE;
    
    public static final BASE58 BTC = new BASE58(BITCOIN);
    public static final BASE58 XRP = new BASE58(RIPPLE);

    public BASE58() {
        this(BITCOIN);
    }

    /**
     * 
     * @param code 符号に使用するASCII文字列 code 127まで サロゲートペア未
     */
    public BASE58(String code) {
        enc = code.toCharArray();
        FE = BigInteger.valueOf(enc.length);
        int max = 0;
        for (int i = 0; i < enc.length; i++) {
            if ( enc[i] > max) {
                max = enc[i];
            }
        }
        max++;
        rbit = new short[max];
        Arrays.fill(rbit, (short)max);
        for (int i = 0; i < enc.length; i++) {
            rbit[enc[i]] = (byte) i;
        }
    }

    /**
     * BASE58 符号化
     *
     * @param bytes 元データ
     * @param offset 符号化開始位置
     * @param length サイズ
     * @return 符号化文字列
     */
    @Override
    public String encode(byte[] bytes, int offset, int length) {
        int zpad = 0;
        byte[] tmp = Arrays.copyOfRange(bytes, offset, offset + length);
        for (int i = 0; i < tmp.length; i++) {
            if (tmp[i] != 0) {
                zpad = i;
                break;
            }
        }
        BigInteger bi = new BigInteger(1, tmp);
        StringBuilder sb = new StringBuilder();

        while (!bi.equals(BigInteger.ZERO)) {
            BigInteger[] dar = bi.divideAndRemainder(FE);
            sb.insert(0, enc[dar[1].intValue()]);
            bi = dar[0];
        }
        if (zpad > 0) {
            char[] t = new char[zpad];
            Arrays.fill(t, enc[0]);
            sb.insert(0, t);
        }
        return sb.toString();
    }

    @Override
    public byte[] decode(String encoded) {
        BigInteger v = BigInteger.ZERO;
        char[] chs = encoded.toCharArray();
        int zpad = chs.length;
        for (int i = 0; i < chs.length; i++) {
            if (chs[i] != enc[0]) {
                zpad = i;
                break;
            }
        }

        for (char ch : chs) {
            if ( ch >= rbit.length) {
                throw new java.lang.IllegalStateException();
            }
            int r = rbit[ch];
            if ( r >= rbit.length ) {
                throw new java.lang.IllegalStateException();
            }
            v = v.multiply(FE).add(BigInteger.valueOf(r));
        }
        int len = (v.bitLength() + 7) / 8;
        byte[] tmp = v.toByteArray();
        if (tmp.length < len + zpad) {
            byte[] n = new byte[len + zpad];
            System.arraycopy(tmp, 0, n, len - tmp.length, tmp.length);
            tmp = n;
        }
        if (tmp.length > len + zpad) {  // 桁数は減ることもありそう
            byte[] n = new byte[len + zpad];
            System.arraycopy(tmp, tmp.length - n.length, n, 0, n.length);
        }
        return tmp;
    }

}