Precompiled contract

Precompiled contract offers a method to program contract using C++. It separates contract logic with data, and has better performance than solidity contract. The update can be achieved by modifying the codes in bottom layer.

Precompied contract and solidity contract

table	precompiled contract	Solidity contract
address	fixed address, defined in codes	confirmed during deployment
contract code	data stored in table, separate with contract, contract logic can be updated	contract variety and data stored in MPT tree
execution	in C++ bottom layer, higher performance, support parallel execution	EVM virtual machine， serial execution

Model structure

The structure of Precompiled is as below:

• Block verifier will verify type of contract by the address of the called contract during transaction execution. Address 1-4 indicates Ethereum Precompile contract; address 0x1000-0x10000 belongs to C++ Precompiled contract, other addresses belong to EVM contract.

Crucial process

• The execution of Precompiled contract needs a object acquired through contract address.

• Each Precompiled contract object will implement call API, in which the detail logic of Precompile contract is implemented.

• call programs according to abi of transaction, acquires Function Selector and parameter, and executes the relative logic.

graph TB Start(Start) --> branch1{Precompiled contract} branch1 --> |Yes|op1[acquire contract object through address] branch1 --> |No|op2[EVM] op1 --> op3[analyze call function and parameter] op3 --> End(return execution result) op2 --> End(return execution result)

API definition

Every Precompiled contract has to realize its own call API, which accepts 3 parameters: ExecutiveContext executive context, abi code of bytesConstRef and exterior account address to judge whether it has write permission.Precompiled source code.

API	Parameter description	Api description
virtual bytes call(std::shared_ptr<ExecutiveContext> context, bytesConstRef param, Address const& origin = Address())	context is block executive context, param is the parameter of abi code, origin is address of the called exterior account	implementation of contract API
virtual uint32_t getParamFunc(bytesConstRef param)	param is the parameter of abi code	acquire Function Select (the former 4 big endian byte of sha3 in function name) of the called function
virtual uint32_t getFuncSelector(std::string const& _functionName)	_functionName is function name	calculate Function Select according to the function name
virtual bytesConstRef getParamData(bytesConstRef param)	param is the parameter of abi code	acquire abi code of parameter of the called function