vm: implement DELEGATECALL

Godeps/_workspace/src/github.com/tendermint/tendermint/vm/vm.go

@@ -147,6 +147,32 @@ func (vm *VM) Call(caller, callee *Account, code, input []byte, value int64, gas
 	return
 }
 
+
+// [This implementation is up for review].
+// DelegateCall is executed by the DELEGATECALL opcode, introduced as off Ethereum Homestead.
+// The intent of delegate call is to run the code of the callee in the storage context of the caller;
+// while preserving the original caller to the previous callee.
+// [ -->] Different to the normal CALL or CALLCODE, the value does not need to be transferred to the callee. [<-- CORRECT?]
+func (vm *VM) DelegateCall(caller, callee *Account, code, input []byte, value int64, gas *int64) (output []byte, err error) {
+	
+	exception := new(string)
+	// fire the post call event (including exception if applicable)
+	defer vm.fireCallEvent(exception, &output, caller, callee, input, value, gas)
+	
+	// DelegateCall does not transfer the value to the callee.
+
+	if len(code) > 0 {
+		vm.callDepth += 1
+		output, err = vm.call(caller, callee, code, input, value, gas)
+		vm.callDepth -= 1
+		if err != nil {
+			*exception = err.Error()
+		}
+	}
+
+	return
+}
+
 // Try to deduct gasToUse from gasLeft.  If ok return false, otherwise
 // set err and return true.
 func useGasNegative(gasLeft *int64, gasToUse int64, err *error) bool {
@@ -799,6 +825,11 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value int64, gas
 						return nil, firstErr(err, ErrUnknownAddress)
 					}
 					ret, err = vm.Call(callee, callee, acc.Code, args, value, gas)
+				} else if op == DELEGATECALL {
+					if acc == nil {
+						return nil, firstErr(err, ErrUnknownAddress)
+					}
+					ret, err = vm.DelegateCall(caller, callee, acc.Code, args, value, gas)
 				} else {
 					// nil account means we're sending funds to a new account
 					if acc == nil {