Implementing OP_2ROT for script operations

src/main/scala/org/scalacoin/script/interpreter/ScriptInterpreter.scala

@@ -52,6 +52,7 @@ trait ScriptInterpreter extends CryptoInterpreter with StackInterpreter with Con
         case OP_PICK :: t => loop(opPick(program))
         case OP_ROLL :: t => loop(opRoll(program))
         case OP_ROT :: t => loop(opRot(program))
+        case OP_2ROT :: t => loop(op2Rot(program))
         //arithmetic operations
         case OP_ADD :: t => loop(opAdd(program))
 

src/main/scala/org/scalacoin/script/stack/StackInterpreter.scala

@@ -153,6 +153,7 @@ trait StackInterpreter {
 
   /**
    * The top three items on the stack are rotated to the left.
+   * x1 x2 x3 -> x2 x3 x1
    * @param program
    * @return
    */
@@ -167,4 +168,21 @@ trait StackInterpreter {
     ScriptProgramImpl(newStack,program.script.tail,program.transaction,program.altStack)
   }
 
+  /**
+   * The fifth and sixth items back are moved to the top of the stack.
+   * x1 x2 x3 x4 x5 x6 -> x3 x4 x5 x6 x1 x2
+   * @param program
+   * @return
+   */
+  def op2Rot(program : ScriptProgram) : ScriptProgram = {
+    require(program.script.headOption.isDefined && program.script.head == OP_2ROT, "Top of script stack must be OP_2ROT")
+    require(program.stack.size > 5,"Stack must have at least 5 items on it for OP_2ROT")
+
+    val newStack = program.stack match {
+      case h :: h1 :: h2 :: h3 :: h4 :: h5 :: t => h4 :: h5 :: h :: h1 :: h2 :: h3 ::  t
+      case _ => throw new RuntimeException("Stack must have at least 5 items on it for OP_2ROT")
+    }
+    ScriptProgramImpl(newStack,program.script.tail,program.transaction,program.altStack)
+  }
+
 }

src/test/scala/org/scalacoin/script/stack/StackInterpreterTest.scala

@@ -149,6 +149,17 @@ class StackInterpreterTest extends FlatSpec with MustMatchers with StackInterpre
 
     newProgram.stack must be (List(ScriptConstantImpl("16"),ScriptConstantImpl("14"),ScriptConstantImpl("15")))
     newProgram.script.isEmpty must be (true)
+  }
 
+  it must "evaluate an OP_2ROT correctly" in {
+    val stack = List(ScriptConstantImpl("14"), ScriptConstantImpl("15"), ScriptConstantImpl("16"),
+      ScriptConstantImpl("17"), ScriptConstantImpl("18"), ScriptConstantImpl("19"))
+    val script = List(OP_2ROT)
+    val program = ScriptProgramImpl(stack,script,TestUtil.transaction,List())
+    val newProgram = op2Rot(program)
+
+    newProgram.stack must be (List(ScriptConstantImpl("18"),ScriptConstantImpl("19"),ScriptConstantImpl("14"),
+      ScriptConstantImpl("15"),ScriptConstantImpl("16"), ScriptConstantImpl("17")))
+    newProgram.script.isEmpty must be (true)
   }
 }