package DNA.Cryptography;

import java.math.BigInteger;

public class Base58 {

/**

* base58编码的字母表

*/

public static final String ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

private static final BigInteger BASE = BigInteger.valueOf(ALPHABET.length());

/**

* 解码

* <param name="input">要解码的字符串</param>

* <returns>返回解码后的字节数组</returns>

*/

public static byte[] decode(String input) {

BigInteger bi = BigInteger.ZERO;

for (int i = input.length() - 1; i >= 0; i--) {

int index = ALPHABET.indexOf(input.charAt(i));

if (index == -1) {

throw new IllegalArgumentException();

}

bi = bi.add(BASE.pow(input.length() - 1 - i).multiply(BigInteger.valueOf(index)));

}

byte[] bytes = bi.toByteArray();

boolean stripSignByte = bytes.length > 1 && bytes[0] == 0 && bytes[1] < 0;

int leadingZeros = 0;

for (; leadingZeros < input.length() && input.charAt(leadingZeros) == ALPHABET.charAt(0); leadingZeros++);

byte[] tmp = new byte[bytes.length - (stripSignByte ? 1 : 0) + leadingZeros];

System.arraycopy(bytes, stripSignByte ? 1 : 0, tmp, leadingZeros, tmp.length - leadingZeros);

return tmp;

}

/**

* 编码

* <param name="input">要编码的字节数组</param>

* <returns>返回编码后的字符串</returns>

*/

public static String encode(byte[] input) {

BigInteger value = new BigInteger(1, input);

StringBuilder sb = new StringBuilder();

while (value.compareTo(BASE) >= 0) {

BigInteger[] r = value.divideAndRemainder(BASE);

sb.insert(0, ALPHABET.charAt(r[1].intValue()));

value = r[0];

}

sb.insert(0, ALPHABET.charAt(value.intValue()));

for (byte b : input) {

if (b == 0) {

sb.insert(0, ALPHABET.charAt(0));

} else {

break;

}

}

return sb.toString();

}

}