thodg/totp-rs

diff --git a/src/rfc.rs b/src/rfc.rs
index 2ad076d..d55bc74 100644
--- a/src/rfc.rs
+++ b/src/rfc.rs
@@ -27,7 +27,7 @@ impl std::fmt::Display for Rfc6238Error {
 }
 
 fn assert_digits(digits: &usize) -> Result<(), Rfc6238Error> {
-    if digits < &6 || digits > &8 {
+    if !(&6..=&8).contains(&digits) {
         Err(Rfc6238Error::InvalidDigits)
     } else {
         Ok(())