a.java

    /**
     * If you know you have an ASCII ByteList you should do something else.  This will continue walking the
     * bytelist 'while' as long as each continues to be true.  When it stops being true it will return the
     * last byte index processed (on full walk it will be length otherwise the beginning of the codepoint
     * which did not satisfy each.
     *
     * @param bytelist of the mbc-laden bytes
     * @param offset place in bytes to search past begin
     * @param each the closure which walks the codepoints
     * @return length if all codepoints match.  index (ignoring begin) if not.
     */
    public static int eachCodePointWhile(ByteList bytelist, int offset, CodePoint each) {
        byte[] bytes = bytelist.unsafeBytes();
        int len = bytelist.getRealSize();
        Encoding encoding = bytelist.getEncoding();
        int begin = bytelist.begin();
        int end = begin + len;
        int n;

        for (int i = 0, p = begin + offset; p < len; i++, p += n) {
            n = StringSupport.length(encoding, bytes, p, end);
            if (!each.call(i, encoding.mbcToCode(bytes, p, end), encoding)) {
                return p;
            }
        }

        return len;
    }