pragma solidity ^0.4.18;

// If you wanna escape this contract REALLY FAST
// 1. open MEW/METAMASK
// 2. Put this as data: 0xb1e35242
// 3. send 150000+ gas
// That calls the getMeOutOfHere() method

contract PowhCoin4 {
    uint256 constant PRECISION = 0x10000000000000000; // 2^64
    int constant CRRN = 1;
    int constant CRRD = 2;
    int constant LOGC = -0x296ABF784A358468C;

    string constant public name = "PowhCoin4";
    string constant public symbol = "POWH4";

    uint8 constant public decimals = 18;
    uint256 public totalSupply;

    // amount of shares for each address (scaled number)
    mapping(address => uint256) public balanceOfOld;

    // allowance map, see erc20
    mapping(address => mapping(address => uint256)) public allowance;

    // amount payed out for each address (scaled number)
    mapping(address => int256) payouts;

    // sum of all payouts (scaled number)
    int256 totalPayouts;

    // amount earned for each share (scaled number)
    uint256 earningsPerShare;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function PowhCoin4() public {
    }

    function balanceOf(address _owner) public constant returns (uint256 balance) {
        return balanceOfOld[_owner];
    }

    function withdraw(uint tokenCount) public returns (bool) {
        var balance = dividends(msg.sender);
        payouts[msg.sender] += (int256) (balance * PRECISION);
        totalPayouts += (int256) (balance * PRECISION);
        msg.sender.transfer(balance);
        return true;
    }

    function sellMyTokensDaddy() public {
        var balance = balanceOf(msg.sender);
        transferTokens(msg.sender, address(this),  balance); // this triggers the internal sell function
    }

    function getMeOutOfHere() public {
        sellMyTokensDaddy();
        withdraw(1); // parameter is ignored
    }

    function fund() public payable returns (bool) {
        if (msg.value > 0.000001 ether)
            buy();
        else
            return false;

        return true;
    }

    function buyPrice() public constant returns (uint) {
        return getTokensForEther(1 finney);
    }

    function sellPrice() public constant returns (uint) {
        return getEtherForTokens(1 finney);
    }

    function transferTokens(address _from, address _to, uint256 _value) internal {
        if (balanceOfOld[_from] < _value)
            revert();
        if (_to == address(this)) {
            sell(_value);
        } else {
            int256 payoutDiff = (int256) (earningsPerShare * _value);
            balanceOfOld[_from] -= _value;
            balanceOfOld[_to] += _value;
            payouts[_from] -= payoutDiff;
            payouts[_to] += payoutDiff;
        }
        Transfer(_from, _to, _value);
    }

    function transfer(address _to, uint256 _value) public {
        transferTokens(msg.sender, _to,  _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public {
        var _allowance = allowance[_from][msg.sender];
        if (_allowance < _value)
            revert();
        allowance[_from][msg.sender] = _allowance - _value;
        transferTokens(_from, _to, _value);
    }

    function approve(address _spender, uint256 _value) public {
        // 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
        if ((_value != 0) && (allowance[msg.sender][_spender] != 0)) revert();
        allowance[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
    }

    function dividends(address _owner) public constant returns (uint256 amount) {
        return (uint256) ((int256)(earningsPerShare * balanceOfOld[_owner]) - payouts[_owner]) / PRECISION;
    }

    function withdrawOld(address to) public {
        var balance = dividends(msg.sender);
        payouts[msg.sender] += (int256) (balance * PRECISION);
        totalPayouts += (int256) (balance * PRECISION);
        to.transfer(balance);
    }

    function balance() internal constant returns (uint256 amount) {
        return this.balance - msg.value;
    }

    function reserve() public constant returns (uint256 amount) {
        return balance() - ((uint256) ((int256) (earningsPerShare * totalSupply) - totalPayouts) / PRECISION) - 1;
    }

    function buy() internal {
        if (msg.value < 0.000001 ether || msg.value > 1000000 ether)
            revert();
        var sender = msg.sender;
        // 5 % of the amount is used to pay holders.
        var fee = (uint)(msg.value / 10);

        // compute number of bought tokens
        var numEther = msg.value - fee;
        var numTokens = getTokensForEther(numEther);

        var buyerfee = fee * PRECISION;
        if (totalSupply > 0) {
            // compute how the fee distributed to previous holders and buyer.
            // The buyer already gets a part of the fee as if he would buy each token separately.
            var holderreward =
                (PRECISION - (reserve() + numEther) * numTokens * PRECISION / (totalSupply + numTokens) / numEther)
                * (uint)(CRRD) / (uint)(CRRD-CRRN);
            var holderfee = fee * holderreward;
            buyerfee -= holderfee;

            // Fee is distributed to all existing tokens before buying
            var feePerShare = holderfee / totalSupply;
            earningsPerShare += feePerShare;
        }
        // add numTokens to total supply
        totalSupply += numTokens;
        // add numTokens to balance
        balanceOfOld[sender] += numTokens;
        // fix payouts so that sender doesn't get old earnings for the new tokens.
        // also add its buyerfee
        var payoutDiff = (int256) ((earningsPerShare * numTokens) - buyerfee);
        payouts[sender] += payoutDiff;
        totalPayouts += payoutDiff;
    }

    function sell(uint256 amount) internal {
        var numEthers = getEtherForTokens(amount);
        // remove tokens
        totalSupply -= amount;
        balanceOfOld[msg.sender] -= amount;

        // fix payouts and put the ethers in payout
        var payoutDiff = (int256) (earningsPerShare * amount + (numEthers * PRECISION));
        payouts[msg.sender] -= payoutDiff;
        totalPayouts -= payoutDiff;
    }

    function getTokensForEther(uint256 ethervalue) public constant returns (uint256 tokens) {
        return fixedExp(fixedLog(reserve() + ethervalue)*CRRN/CRRD + LOGC) - totalSupply;
    }

    function getEtherForTokens(uint256 tokens) public constant returns (uint256 ethervalue) {
        if (tokens == totalSupply)
            return reserve();
        return reserve() - fixedExp((fixedLog(totalSupply - tokens) - LOGC) * CRRD/CRRN);
    }

    int256 constant one       = 0x10000000000000000;
    uint256 constant sqrt2    = 0x16a09e667f3bcc908;
    uint256 constant sqrtdot5 = 0x0b504f333f9de6484;
    int256 constant ln2       = 0x0b17217f7d1cf79ac;
    int256 constant ln2_64dot5= 0x2cb53f09f05cc627c8;
    int256 constant c1        = 0x1ffffffffff9dac9b;
    int256 constant c3        = 0x0aaaaaaac16877908;
    int256 constant c5        = 0x0666664e5e9fa0c99;
    int256 constant c7        = 0x049254026a7630acf;
    int256 constant c9        = 0x038bd75ed37753d68;
    int256 constant c11       = 0x03284a0c14610924f;

    function fixedLog(uint256 a) internal pure returns (int256 log) {
        int32 scale = 0;
        while (a > sqrt2) {
            a /= 2;
            scale++;
        }
        while (a <= sqrtdot5) {
            a *= 2;
            scale--;
        }
        int256 s = (((int256)(a) - one) * one) / ((int256)(a) + one);
        // The polynomial R = c1*x + c3*x^3 + ... + c11 * x^11
        // approximates the function log(1+x)-log(1-x)
        // Hence R(s) = log((1+s)/(1-s)) = log(a)
        var z = (s*s) / one;
        return scale * ln2 +
            (s*(c1 + (z*(c3 + (z*(c5 + (z*(c7 + (z*(c9 + (z*c11/one))
                /one))/one))/one))/one))/one);
    }

    int256 constant c2 =  0x02aaaaaaaaa015db0;
    int256 constant c4 = -0x000b60b60808399d1;
    int256 constant c6 =  0x0000455956bccdd06;
    int256 constant c8 = -0x000001b893ad04b3a;

    function fixedExp(int256 a) internal pure returns (uint256 exp) {
        int256 scale = (a + (ln2_64dot5)) / ln2 - 64;
        a -= scale*ln2;
        // The polynomial R = 2 + c2*x^2 + c4*x^4 + ...
        // approximates the function x*(exp(x)+1)/(exp(x)-1)
        // Hence exp(x) = (R(x)+x)/(R(x)-x)
        int256 z = (a*a) / one;
        int256 R = ((int256)(2) * one) +
            (z*(c2 + (z*(c4 + (z*(c6 + (z*c8/one))/one))/one))/one);
        exp = (uint256) (((R + a) * one) / (R - a));
        if (scale >= 0)
            exp <<= scale;
        else
            exp >>= -scale;
        return exp;
    }

    function () payable public {
        if (msg.value > 0)
            buy();
        else
            withdrawOld(msg.sender);
    }
}