tornado-core/contracts/ETHMixer.sol

// https://tornado.cash
/*
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*    88    88.  .88 88       88    88 88.  .88 88.  .88 88.  .88 dP Y8.   .88 88.  .88       88 88    88
*    dP    `88888P' dP       dP    dP `88888P8 `88888P8 `88888P' 88  Y88888P' `88888P8 `88888P' dP    dP
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*/

pragma solidity ^0.5.8;

import "./Mixer.sol";

contract ETHMixer is Mixer {

  constructor(
    address _verifier,
    uint256 _transferValue,
    uint8 _merkleTreeHeight,
    uint256 _emptyElement,
    address payable _operator
  ) Mixer(_verifier, _transferValue, _merkleTreeHeight, _emptyElement, _operator) public {}

  function deposit(uint256 commitment) public payable {
    require(msg.value == transferValue, "Please send `transferValue` ETH along with transaction");
    _deposit(commitment);

    emit Deposit(commitment, next_index - 1, block.timestamp);
  }

  function withdraw(uint256[2] memory a, uint256[2][2] memory b, uint256[2] memory c, uint256[4] memory input) public {
    _withdraw(a, b, c, input);
    address payable receiver = address(input[2]);
    uint256 fee = input[3];
    uint256 nullifierHash = input[1];

    require(fee < transferValue, "Fee exceeds transfer value");
    receiver.transfer(transferValue - fee);
    if (fee > 0) {
      operator.transfer(fee);
    }

    emit Withdraw(receiver, nullifierHash, fee);
  }
}