yield op code for yielding coroutine computation

core/vm/instructions.go

@@ -817,6 +817,26 @@ func opStaticCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext)
 	return ret, nil
 }
 
+func opYield(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
+  // Save current Environment as coroutine
+  coroutine := NewCoroutine(*pc + 1, *scope.Stack)
+
+  // Push coroutine to the stack
+  scope.PushCoroutine(coroutine)
+
+  log.Printf("Coroutine %d yielded with %v", coroutine.PC, coroutine.Stack)
+
+  // Call the next coroutine
+  nextCoroutine, err := scope.PopCoroutine()
+  if err != nil {
+    return nil, err
+  }
+  ret, err := nextCoroutine.ExecuteCoroutine(interpreter, scope)
+  log.Printf("Coroutine %d returned with %v", nextCoroutine.PC, ret)
+
+  return nil, errStopToken
+}
+
 func opReturn(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
 	offset, size := scope.Stack.pop(), scope.Stack.pop()
 	ret := scope.Memory.GetPtr(int64(offset.Uint64()), int64(size.Uint64()))

core/vm/interpreter.go

@@ -275,7 +275,6 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		err = nil // clear stop token error
 	}
 
-  log2.Println("returning from run with", res, err)
   // Res is array of bytes located in scope.Memory
 	return res, err
 }

core/vm/jump_table.go

@@ -1044,6 +1044,12 @@ func newFrontierInstructionSet() JumpTable {
 			maxStack:    maxStack(7, 1),
 			memorySize:  memoryCall,
 		},
+    YIELD: {
+      execute:     opYield,
+      constantGas: 1, //TODO: set this to something reasonable
+      minStack:    minStack(0, 0),
+      maxStack:    maxStack(0, 0),
+    },
 		RETURN: {
 			execute:    opReturn,
 			dynamicGas: gasReturn,

core/vm/opcodes.go

@@ -219,6 +219,7 @@ const (
 
 	STATICCALL   OpCode = 0xfa
   SPAWN        OpCode = 0xfb
+  YIELD        OpCode = 0xfc
 	REVERT       OpCode = 0xfd
 	INVALID      OpCode = 0xfe
 	SELFDESTRUCT OpCode = 0xff
@@ -393,6 +394,7 @@ var opCodeToString = map[OpCode]string{
 	DELEGATECALL: "DELEGATECALL",
 	CREATE2:      "CREATE2",
 	STATICCALL:   "STATICCALL",
+  YIELD:        "YIELD",
 	REVERT:       "REVERT",
 	INVALID:      "INVALID",
 	SELFDESTRUCT: "SELFDESTRUCT",
@@ -448,6 +450,7 @@ var stringToOp = map[string]OpCode{
 	"BLOBHASH":       BLOBHASH,
 	"DELEGATECALL":   DELEGATECALL,
 	"STATICCALL":     STATICCALL,
+  "YIELD":          YIELD,
 	"CODESIZE":       CODESIZE,
 	"CODECOPY":       CODECOPY,
 	"GASPRICE":       GASPRICE,