minor hash improvements

data/HashMap.h

@@ -247,10 +247,14 @@ private:
     }
 
     Hash fullHash(int key) const {
+        static_assert(sizeof(key) == sizeof(Hash),
+                      "unwanted loose of precision in hash");
         return key;
     }
 
     Hash fullHash(unsigned int key) const {
+        static_assert(sizeof(key) == sizeof(Hash),
+                      "unwanted loose of precision in hash");
         return key;
     }
 

utils/StringBuffer.h

@@ -17,7 +17,7 @@ class StringBuffer final {
     char data[N];
 
     void addToHash(char c) {
-        hash = 2120251889 * hash + c;
+        hash = static_cast<Hash>(2120251889) * hash + static_cast<Hash>(c);
     }
 
     void addToHash(int from, int to) {