private static boolean[] parseCharsetBitmap(Environment env, TraceInfo trace, String charset) {
        boolean[] bitmap = new boolean[256];

        int length = charset.length();
        for (int i = 0; i < length; i++) {
            char ch = charset.charAt(i);

            // XXX: the bitmap eventual might need to deal with unicode
            if (ch >= 256)
                continue;

            bitmap[ch] = true;

            if (length <= i + 3)
                continue;

            if (charset.charAt(i + 1) != '.' || charset.charAt(i + 2) != '.')
                continue;

            char last = charset.charAt(i + 3);

            if (last < ch) {
                env.warning(trace, "character set range is invalid: %s..%s", ch, last);
                continue;
            }

            i += 3;
            for (; ch <= last; ch++) {
                bitmap[ch] = true;
            }

            // TODO: handling of '@'?
        }

        return bitmap;
    }
Parses the cslashes bitmap returning an actual bitmap.

@param charset the bitmap string

@return the actual bitmap
exts/jphp-zend-ext/src/main/java/org/develnext/jphp/zend/ext/standard/StringFunctions.java