@Immutable
    public static Memory strrpos(Environment env, TraceInfo trace, String haystack, Memory needle) {
        return strrpos(env, trace, haystack, needle, null);
    }
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