CGI::Escape#unescapeURIComponent

static VALUE
cgiesc_unescape_uri_component(int argc, VALUE *argv, VALUE self)
{
    VALUE str = (rb_check_arity(argc, 1, 2), argv[0]);

    StringValue(str);

    if (rb_enc_str_asciicompat_p(str)) {
        VALUE enc = accept_charset(argc-1, argv+1, self);
        return optimized_unescape(str, enc, 0);
    }
    else {
        return rb_call_super(argc, argv);
    }
}