update rpuzzle

docs/rpuzzle.rst

@@ -11,19 +11,14 @@ More information can be found in the `R-Puzzle`_ talk.
     contract RPuzzle {
         Ripemd160 rhash;
 
-        constructor(Ripemd160 rhash) {
-            this.rhash = rhash;
-        }
-
-        function getSigR(Sig sigr): bytes {
-            bytes lenBytes = sigr[3:4];
-            int len = unpack(lenBytes);
-            bytes r = sigr[4:4+len];
-            return r;
+        // extract r from DER-encoded signature
+        static function extractRFromSig(Sig sig) : bytes {
+            int rlen = unpack(sig[3 : 4]);
+            return sig[4 : 4 + rlen];
         }
 
         public function unlock(Sig sig, PubKey pubKey, Sig sigr) {
-            require(this.rhash == hash160(this.getSigR(sigr)));
+            require(this.rhash == hash160(extractRFromSig(sigr)));
             require(checkSig(sigr, pubKey));
             require(checkSig(sig, pubKey));
         }