CompactEncoder.java

package org.ripple.power.blockchain.list;

import static org.ripple.bouncycastle.util.Arrays.concatenate;
import static org.ripple.bouncycastle.util.encoders.Hex.encode;

import java.io.ByteArrayOutputStream;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

import org.ripple.power.utils.ByteUtils;

public class CompactEncoder {

	private final static byte TERMINATOR = 16;
	private final static Map<Character, Byte> hexMap = new HashMap<Character, Byte>();
	static {
		hexMap.put('0', (byte) 0x0);
		hexMap.put('1', (byte) 0x1);
		hexMap.put('2', (byte) 0x2);
		hexMap.put('3', (byte) 0x3);
		hexMap.put('4', (byte) 0x4);
		hexMap.put('5', (byte) 0x5);
		hexMap.put('6', (byte) 0x6);
		hexMap.put('7', (byte) 0x7);
		hexMap.put('8', (byte) 0x8);
		hexMap.put('9', (byte) 0x9);
		hexMap.put('a', (byte) 0xa);
		hexMap.put('b', (byte) 0xb);
		hexMap.put('c', (byte) 0xc);
		hexMap.put('d', (byte) 0xd);
		hexMap.put('e', (byte) 0xe);
		hexMap.put('f', (byte) 0xf);
	}

	public static byte[] packNibbles(byte[] nibbles) {
		int terminator = 0;
		if (nibbles[nibbles.length - 1] == TERMINATOR) {
			terminator = 1;
			nibbles = Arrays.copyOf(nibbles, nibbles.length - 1);
		}
		int oddlen = nibbles.length % 2;
		int flag = 2 * terminator + oddlen;
		if (oddlen != 0) {
			byte[] flags = new byte[] { (byte) flag };
			nibbles = concatenate(flags, nibbles);
		} else {
			byte[] flags = new byte[] { (byte) flag, 0 };
			nibbles = concatenate(flags, nibbles);
		}
		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
		for (int i = 0; i < nibbles.length; i += 2) {
			buffer.write(16 * nibbles[i] + nibbles[i + 1]);
		}
		return buffer.toByteArray();
	}

	public static byte[] unpackToNibbles(byte[] str) {
		byte[] base = binToNibbles(str);
		base = Arrays.copyOf(base, base.length - 1);
		if (base[0] >= 2) {
			base = ByteUtils.appendByte(base, TERMINATOR);
		}
		if (base[0] % 2 == 1) {
			base = Arrays.copyOfRange(base, 1, base.length);
		} else {
			base = Arrays.copyOfRange(base, 2, base.length);
		}
		return base;
	}

	public static byte[] binToNibbles(byte[] str) {
		byte[] hexEncoded = encode(str);
		ByteBuffer slice = ByteBuffer.allocate(hexEncoded.length + 1);
		for (byte b : hexEncoded) {
			slice.put(hexMap.get((char) b));
		}
		slice.put(TERMINATOR);
		return slice.array();
	}

	public static byte[] binToNibblesNoTerminator(byte[] str) {
		byte[] hexEncoded = encode(str);
		ByteBuffer slice = ByteBuffer.allocate(hexEncoded.length);
		for (byte b : hexEncoded) {
			slice.put(hexMap.get((char) b));
		}
		return slice.array();
	}
}