// http://icu-project.org/docs/papers/gb18030.html#h7
// uFirst = 0x10000;
// bFirst = [0x90, 0x30, 0x81, 0x30];

int linear(byte bytes[4]) {
    return ((bytes[0]*10+bytes[1])*126+bytes[2])*10+bytes[3];
}

 int mapToUnicode(byte bytes[4]) {
    int lin=linear(bytes);
    for each range {
        if(linear(bFirst)<=lin&lt=linear(bLast)) {
            // range found
            return uFirst+(lin-linear(bFirst));
        }
    }
    // the byte sequence is not in any known range
    return error;
}