// Copyright (C) 2003 Adam Megacz <adam@xwt.org> all rights reserved.
//
// You may modify, copy, and redistribute this code under the terms of
// the GNU Library Public License version 2.1, with the exception of
// the portion of clause 6a after the semicolon (aka the "obnoxious
// relink clause")

package org.xwt.util;
import java.io.*;
import java.util.*;

/** packs 8-bit bytes into a String of 7-bit chars (to avoid the UTF-8 non-ASCII penalty) */
public class PackBytesIntoString {

    public static String pack(byte[] b, int off, int len) throws IllegalArgumentException {
        if (len % 7 != 0) throw new IllegalArgumentException("len must be a multiple of 7");
        StringBuffer ret = new StringBuffer();
        for(int i=off; i<off+len; i += 7) {
            long l = 0;
            for(int j=6; j>=0; j--) {
                l <<= 8;
                l |= (b[i + j] & 0xff);
            }
            for(int j=0; j<8; j++) {
                ret.append((char)(l & 0x7f));
                l >>= 7;
            }
        }
        return ret.toString();
    }

    public static byte[] unpack(String s) throws IllegalArgumentException {
        if (s.length() % 8 != 0) throw new IllegalArgumentException("string length must be a multiple of 8");
        byte[] ret = new byte[(s.length() / 8) * 7];
        for(int i=0; i<s.length(); i += 8) {
            long l = 0;
            for(int j=7; j>=0; j--) {
                l <<= 7;
                l |= (s.charAt(i + j) & 0x7fL);
            }
            for(int j=0; j<7; j++) {
                ret[(i / 8) * 7 + j] = (byte)(l & 0xff);
                l >>= 8;
            }
        }
        return ret;
    }
}