ens-usernames/contracts/token/StandardToken.sol

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pragma solidity ^0.4.23;
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import "./ERC20Token.sol";
contract StandardToken is ERC20Token {
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uint256 private supply;
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mapping (address => uint256) balances;
mapping (address => mapping (address => uint256)) allowed;
constructor() internal { }
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function transfer(
address _to,
uint256 _value
)
external
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returns (bool success)
{
return transfer(msg.sender, _to, _value);
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}
/**
* @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
* @param _spender The address which will spend the funds.
* @param _value The amount of tokens to be spent.
*/
function approve(address _spender, uint256 _value) returns (bool) {
// To change the approve amount you first have to reduce the addresses`
// allowance to zero by calling `approve(_spender, 0)` if it is not
// already 0 to mitigate the race condition described here:
// https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
require((_value == 0) || (allowed[msg.sender][_spender] == 0));
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}
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function transferFrom(
address _from,
address _to,
uint256 _value
)
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external
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returns (bool success)
{
if (balances[_from] >= _value &&
allowed[_from][msg.sender] >= _value &&
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_value > 0) {
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allowed[_from][msg.sender] -= _value;
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return transfer(_from, _to, _value);
} else {
return false;
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}
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}
function allowance(address _owner, address _spender)
external
view
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returns (uint256 remaining)
{
return allowed[_owner][_spender];
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}
function balanceOf(address _owner)
external
view
returns (uint256 balance)
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{
return balances[_owner];
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}
function totalSupply()
external
view
returns(uint256 currentTotalSupply)
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{
return supply;
}
function mint(
address _to,
uint256 _amount
)
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internal
{
balances[_to] += _amount;
supply += _amount;
emit Transfer(0x0, _to, _amount);
}
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function transfer(
address _from,
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address _to,
uint256 _value
)
internal
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returns (bool success)
{
if (balances[_from] >= _value && _value > 0) {
balances[_from] -= _value;
balances[_to] += _value;
emit Transfer(_from, _to, _value);
return true;
} else {
return false;
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}
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}
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}