GasRefund

GasRefund.sol

contract GasRefund {
    uint256 private _begin;
    uint256 private _end;
    
    function refundSupply() public view returns(uint256 supply) {
        return _end - _begin;
    }
    
    function burn(uint256 n) internal {
        uint256 begin = _begin;
        require(begin + n <= _end);
        for (uint i = begin; i < begin + n; i++) {
            _addressFrom(i).call("");
        }
        _begin = begin + n;
    }
    
    function mint(uint256 n) internal {
        for (uint i = 0; i < n; i++) {
            _makeChild();
        }
        _end += n;
    }
    
    function _makeChild() private returns (address addr) {
        assembly {
            // EVM assembler of runtime portion of child contract:
            //     ;; Pseudocode: if (msg.sender != 0x0000000000b3f879cb30fe243b4dfee438691c04) { throw; }
            let mem_ptr := mload(0x40)
            mstore(mem_ptr, 0x00756eb3f879cb30fe243b4dfee438691c043318585733ff6000526016600af3)
            addr := create(0, add(mem_ptr, 1), 31)
        }
    }
    
    function _addressFrom(uint _nonce) private view returns(address) {
        if(_nonce == 0x00)     return address(bytes20(keccak256(abi.encodePacked(byte(0xd6), byte(0x94), address(this), byte(0x80)))));
        if(_nonce <= 0x7f)     return address(bytes20(keccak256(abi.encodePacked(byte(0xd6), byte(0x94), address(this), uint8(_nonce)))));
        if(_nonce <= 0xff)     return address(bytes20(keccak256(abi.encodePacked(byte(0xd7), byte(0x94), address(this), byte(0x81), uint8(_nonce)))));
        if(_nonce <= 0xffff)   return address(bytes20(keccak256(abi.encodePacked(byte(0xd8), byte(0x94), address(this), byte(0x82), uint16(_nonce)))));
        if(_nonce <= 0xffffff) return address(bytes20(keccak256(abi.encodePacked(byte(0xd9), byte(0x94), address(this), byte(0x83), uint24(_nonce)))));
        return address(bytes20(keccak256(abi.encodePacked(byte(0xda), byte(0x94), address(this), byte(0x84), uint32(_nonce))))); // more than 2^32 nonces not realistic
    }
    
    function addressFrom() public view returns(address) {
        return _addressFrom(0);
    }
}