test that invalid RegSpec constructions panic as expected

in the process, fix 64-bit rex-byte limit, 32/16-bit mode mask reg limit

1 files changed, 1 insertions, 1 deletions

diff --git a/src/real_mode/mod.rs b/src/real_mode/mod.rs
index 92c0592..74e1c37 100644
--- a/src/real_mode/mod.rs
+++ b/src/real_mode/mod.rs
@@ -179,7 +179,7 @@ impl RegSpec {
     /// construct a `RegSpec` for mask reg `num`
     #[inline]
     pub fn mask(num: u8) -> RegSpec {
-        if num >= 32 {
+        if num >= 8 {
             panic!("invalid x86 mask reg {}", num);
         }