private static int hexDigit(int c) {
        if ('0' <= c && c <= '9') {
            return c - '0';
        } else if ('a' <= c && c <= 'f') {
            return c - 'a' + 10;
        } else if ('A' <= c && c <= 'F') {
            return c - 'A' + 10;
        } else {
            return 0;
        }
    }
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