Update CREATE2 gas cost calculation

Fixes #1346

eth/vm/logic/system.py

@@ -17,6 +17,9 @@
 from eth.utils.hexadecimal import (
     encode_hex,
 )
+from eth.utils.numeric import (
+    ceil32,
+)
 from eth.vm import mnemonics
 from eth.vm.computation import (
     BaseComputation
@@ -120,6 +123,9 @@ class Create(Opcode):
     def max_child_gas_modifier(self, gas: int) -> int:
         return gas
 
+    def get_gas_cost(self, data: CreateOpcodeStackData) -> int:
+        return self.gas_cost
+
     def generate_contract_address(self,
                                   stack_data: CreateOpcodeStackData,
                                   call_data: bytes,
@@ -144,10 +150,12 @@ def get_stack_data(self, computation: BaseComputation) -> CreateOpcodeStackData:
         return CreateOpcodeStackData(endowment, memory_start, memory_length)
 
     def __call__(self, computation: BaseComputation) -> None:
-        computation.consume_gas(self.gas_cost, reason=self.mnemonic)
 
         stack_data = self.get_stack_data(computation)
 
+        gas_cost = self.get_gas_cost(stack_data)
+        computation.consume_gas(gas_cost, reason=self.mnemonic)
+
         computation.extend_memory(stack_data.memory_start, stack_data.memory_length)
 
         insufficient_funds = computation.state.account_db.get_balance(
@@ -219,6 +227,9 @@ def get_stack_data(self, computation: BaseComputation) -> CreateOpcodeStackData:
 
         return CreateOpcodeStackData(endowment, memory_start, memory_length, salt)
 
+    def get_gas_cost(self, data: CreateOpcodeStackData) -> int:
+        return constants.GAS_SHA3WORD * ceil32(data.memory_length) // 32
+
     def generate_contract_address(self,
                                   stack_data: CreateOpcodeStackData,
                                   call_data: bytes,