diff --git a/register.py b/register.py
index 2e6b700..67deaa5 100644
--- a/register.py
+++ b/register.py
@@ -10,16 +10,19 @@ class Register:
         self.value = 0
         Register.registers.append(self)
 
-    def truncate(self, value, bits=None):
+    def truncate_val(self, value, bits=None):
         if bits is None:
             bits = self.n_bits
-        return value & (1 << bits - 1)
+        return value & ((1 << bits) - 1)
+
+    def trucate(self):
+        self.value = self.truncate_val(self.value)
 
     def set(self, value):
         if value < 0:
-            self.value = self.truncate(abs(value), self.n_bits - 1)
+            self.value = self.truncate_val(abs(value), self.n_bits - 1)
             self.negate()
-        self.value = self.truncate(value)
+        self.trucate()
 
     def get(self):
         return self.value