C++ Engine¶

Tags: “Precompiled Contracts” “Smart Contracts” “Precompiled”

Precompiled contracts provide a way to use C++The method of writing contracts, which separates contract logic from data, has better performance than solidity contracts, and can be upgraded by modifying the underlying code。

Precompiled Contracts vs. Solidity Contracts¶

Table Name	Precompiled Contracts	Solidity Contract
Address	Fixed address, defined in code	Determine when deploying
Contract Code	Data is stored in tables, separated from contracts, and contract logic can be upgraded	Contract variables and data are stored in the MPT tree
Execute	C++Low-level execution for higher performance and parallelism	EVM virtual machine, serial execution

Module Architecture¶

The architecture of Precompiled is shown in the following figure:

The block validator determines the type based on the address of the called contract when executing the transaction。Addresses 1-4 represent Ethereum precompiled contracts, addresses 0x1000-0x10000 are C++Precompiled contracts, other addresses are EVM contracts。

Key Processes¶

When executing a precompiled contract, you first need to get the object of the precompiled contract based on the contract address。
Each precompiled contract object implements the ‘call’ interface, where the specific logic of the precompiled contract is implemented。
‘call’ obtains the ‘Function Selector’ and parameters according to the abi code of the transaction, and then executes the corresponding logic。

    graph LR
        Start(Commencement) --> branch1{Precompiled Contracts}
        branch1 --> |Yes|op1 [Get contract object by address]
        branch1 --> |否|op2[EVM]
        op1 --> op3 [Parse Call Function and Parameters]
        op3 --> End(Return execution result)
        op2 --> End(Return execution result)

Interface Definition¶

Each precompiled contract must implement its own ‘call’ interface, which accepts two parameters, namely ‘TransactionExecutive::Ptr’Execution Context, ‘PrecompiledExecResult::Ptr ‘execution parameters, which include execution input, external account address, gas usage。’Precompiled’ source code。

Interface Name	Parameter Description	Interface Description
`PrecompiledExecResult::Ptr call(executor::TransactionExecutive::Ptr context,PrecompiledExecResult::Ptr param) override;`	'context 'is the block execution context, and' param 'is the execution parameters, including the execution input, external account address, and gas usage	Implementation of specific contract interfaces
`uint32_t getFuncSelector(std::string const& functionName)`	'functionName 'is the function name	Calculate 'Function Select' based on function name
`bytesConstRef getParamData(bytesConstRef param)`	'param 'is an abi-encoded parameter	Obtain the abi encoding of the specific parameters of the calling function
`uint32_t getParamFunc(bytesConstRef param)`	'param 'is an abi-encoded parameter	Get the 'Function Select' of the called function (the first four bytes of sha3 of the function name)