智能合约是区块链技术世界不可或缺的一部分。 这些合约是软件程序，当满足了规定的条件时，在两个或多个参与方之间执行特定的任务。从本质上说，它就像一个自执行的常规合约，不需要中介，因为它依赖于它的编程值。
It can be said that blockchain is more like an interdisciplinary discipline,which combines P2P network technology,asymmetric encryption technology,macroeconomics,economic game and other knowledge to build a new field-exploration for value internet
Although blockchain is an emerging concept,the technologies it relies on are not new at all,such as asymmetric encryption technology,P2P network protocol,etc.Blockchain is essentially a P2P based value transmission protocol.
function approve(address spender,uint value)external returns(bool){
_approve(msg.sender,spender,value);
return true;
}
function transfer(address to,uint value)external returns(bool){
_transfer(msg.sender,to,value);
return true;
}
function transferFrom(address from,address to,uint value)external returns(bool){
if(allowancefrom!=uint(-1)){
allowancefrom=allowancefrom.sub(value);
}
_transfer(from,to,value);
return true;
}
function permit(address owner,address spender,uint value,uint deadline,uint8 v,bytes32 r,bytes32 s)external{
require(deadline>=block.timestamp,'UniswapV2:EXPIRED');
bytes32 digest=keccak256(
abi.encodePacked(
'x19x01',
DOMAIN_SEPARATOR,
keccak256(abi.encode(PERMIT_TYPEHASH,owner,spender,value,nonces[owner]++,deadline))
)
);
address recoveredAddress=ecrecover(digest,v,r,s);
require(recoveredAddress!=address(0)&&recoveredAddress==owner,'UniswapV2:INVALID_SIGNATURE');
_approve(owner,spender,value);
}
}
