tornado-core/contracts/ETHMixer.sol

// https://tornado.cash
/*
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*    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(
    IVerifier _verifier,
    uint256 _denomination,
    uint32 _merkleTreeHeight,
    address _operator
  ) Mixer(_verifier, _denomination, _merkleTreeHeight, _operator) public {
  }

  function _processDeposit() internal {
    require(msg.value == denomination, "Please send `mixDenomination` ETH along with transaction");
  }

  function _processWithdraw(address payable _recipient, address payable _relayer, uint256 _fee, uint256 _refund) internal {
    // sanity checks
    require(msg.value == 0, "Message value is supposed to be zero for ETH mixer");
    require(_refund == 0, "Refund value is supposed to be zero for ETH mixer");

    _recipient.transfer(denomination - _fee);
    if (_fee > 0) {
      _relayer.transfer(_fee);
    }
  }
}