Module#<=

VALUE
rb_class_inherited_p(VALUE mod, VALUE arg)
{
    if (mod == arg) return Qtrue;

    if (RB_TYPE_P(arg, T_CLASS) && RB_TYPE_P(mod, T_CLASS)) {
        // comparison between classes
        size_t mod_depth = RCLASS_SUPERCLASS_DEPTH(mod);
        size_t arg_depth = RCLASS_SUPERCLASS_DEPTH(arg);
        if (arg_depth < mod_depth) {
            // check if mod < arg
            return RCLASS_SUPERCLASSES(mod)[arg_depth] == arg ?
                Qtrue :
                Qnil;
        }
        else if (arg_depth > mod_depth) {
            // check if mod > arg
            return RCLASS_SUPERCLASSES(arg)[mod_depth] == mod ?
                Qfalse :
                Qnil;
        }
        else {
            // Depths match, and we know they aren't equal: no relation
            return Qnil;
        }
    }
    else {
        if (!CLASS_OR_MODULE_P(arg) && !RB_TYPE_P(arg, T_ICLASS)) {
            rb_raise(rb_eTypeError, "compared with non class/module");
        }
        if (class_search_ancestor(mod, RCLASS_ORIGIN(arg))) {
            return Qtrue;
        }
        /* not mod < arg; check if mod > arg */
        if (class_search_ancestor(arg, mod)) {
            return Qfalse;
        }
        return Qnil;
    }
}