Precompiled contract & Depth change

* Added pre-compiled contract 0x04 (mem cpy)
* Changed depth error to return the gas instead of consuming

core/execution.go

@@ -36,7 +36,8 @@ func (self *Execution) exec(code, contextAddr []byte, caller vm.ContextRef) (ret
 	evm := vm.New(env, vm.DebugVmTy)
 
 	if env.Depth() == vm.MaxCallDepth {
-		// Consume all gas (by not returning it) and return a depth error
+		caller.ReturnGas(self.Gas, self.price)
+
 		return nil, vm.DepthError{}
 	}
 

vm/address.go

@@ -21,19 +21,31 @@ func (self PrecompiledAccount) Call(in []byte) []byte {
 }
 
 var Precompiled = map[string]*PrecompiledAccount{
+	// ECRECOVER
 	string(ethutil.LeftPadBytes([]byte{1}, 20)): &PrecompiledAccount{func(l int) *big.Int {
 		return GasEcrecover
 	}, ecrecoverFunc},
+
+	// SHA256
 	string(ethutil.LeftPadBytes([]byte{2}, 20)): &PrecompiledAccount{func(l int) *big.Int {
 		n := big.NewInt(int64(l+31)/32 + 1)
 		n.Mul(n, GasSha256)
 		return n
 	}, sha256Func},
+
+	// RIPEMD160
 	string(ethutil.LeftPadBytes([]byte{3}, 20)): &PrecompiledAccount{func(l int) *big.Int {
 		n := big.NewInt(int64(l+31)/32 + 1)
 		n.Mul(n, GasRipemd)
 		return n
 	}, ripemd160Func},
+
+	string(ethutil.LeftPadBytes([]byte{4}, 20)): &PrecompiledAccount{func(l int) *big.Int {
+		n := big.NewInt(int64(l+31)/32 + 1)
+		n.Mul(n, GasMemCpy)
+
+		return n
+	}, memCpy},
 }
 
 func sha256Func(in []byte) []byte {
@@ -54,3 +66,7 @@ func ecrecoverFunc(in []byte) []byte {
 
 	return ethutil.LeftPadBytes(crypto.Sha3(crypto.Ecrecover(append(hash, sig...))[1:])[12:], 32)
 }
+
+func memCpy(in []byte) []byte {
+	return in
+}

vm/common.go

@@ -38,6 +38,7 @@ var (
 	GasSha256       = big.NewInt(50)
 	GasRipemd       = big.NewInt(50)
 	GasEcrecover    = big.NewInt(500)
+	GasMemCpy       = big.NewInt(1)
 
 	Pow256 = ethutil.BigPow(2, 256)