Bugfix-- registers now appropriately truncated.

git-svn-id: http://www.cdkersey.com/harp/harptool@117 0246edb2-e076-4747-b392-db732a341fa2

src/include/core.h

@@ -24,8 +24,14 @@ namespace Harp {
     Reg(Word c, Word n): cpuId(c), regNum(n), val(0) {}
 
     Reg &operator=(T r) { val = r; doWrite(); return *this; }
+
     operator T() { doRead(); return val; }
 
+    void trunc(Size s) {
+      Word mask((~0ull >> (sizeof(Word)-s)*8));
+      val &= mask;
+    }
+
   private:
     Word cpuId, regNum;
     T val;