erc20-demurrage-token/solidity/DemurrageTokenSingleNocap.sol

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pragma solidity > 0.6.11;
// SPDX-License-Identifier: GPL-3.0-or-later
contract DemurrageTokenSingleNocap {
// Redistribution bit field, with associated shifts and masks
// (Uses sub-byte boundaries)
bytes32[] public redistributions; // uint95(unused) | uint20(demurrageModifier) | uint36(participants) | uint72(value) | uint32(period)
uint8 constant shiftRedistributionPeriod = 0;
uint256 constant maskRedistributionPeriod = 0x00000000000000000000000000000000000000000000000000000000ffffffff; // (1 << 32) - 1
uint8 constant shiftRedistributionValue = 32;
uint256 constant maskRedistributionValue = 0x00000000000000000000000000000000000000ffffffffffffffffff00000000; // ((1 << 72) - 1) << 32
uint8 constant shiftRedistributionDemurrage = 140;
uint256 constant maskRedistributionDemurrage = 0x000000000000000000000000fffff00000000000000000000000000000000000; // ((1 << 20) - 1) << 140
// Account balances
mapping (address => uint256) account;
// Cached demurrage amount, ppm with 38 digit resolution
uint128 public demurrageAmount;
// Cached demurrage period; the period for which demurrageAmount was calculated
uint128 public demurragePeriod;
// Implements EIP172
address public owner;
address newOwner;
// Implements ERC20
string public name;
// Implements ERC20
string public symbol;
// Implements ERC20
uint256 public decimals;
// Implements ERC20
uint256 public totalSupply;
// Minimum amount of (demurraged) tokens an account must spend to participate in redistribution for a particular period
uint256 public minimumParticipantSpend;
// 128 bit resolution of the demurrage divisor
// (this constant x 1000000 is contained within 128 bits)
uint256 constant ppmDivider = 100000000000000000000000000000000;
// Timestamp of start of periods (time which contract constructor was called)
uint256 public immutable periodStart;
// Duration of a single redistribution period in seconds
uint256 public immutable periodDuration;
// Demurrage in ppm per minute
uint256 public immutable taxLevel;
// Addresses allowed to mint new tokens
mapping (address => bool) minter;
// Storage for ERC20 approve/transferFrom methods
mapping (address => mapping (address => uint256 ) ) allowance; // holder -> spender -> amount (amount is subject to demurrage)
// Address to send unallocated redistribution tokens
address sinkAddress;
// Implements ERC20
event Transfer(address indexed _from, address indexed _to, uint256 _value);
// Implements ERC20
event Approval(address indexed _owner, address indexed _spender, uint256 _value);
// New tokens minted
event Mint(address indexed _minter, address indexed _beneficiary, uint256 _value);
// New demurrage cache milestone calculated
event Decayed(uint256 indexed _period, uint256 indexed _periodCount, uint256 indexed _oldAmount, uint256 _newAmount);
// When a new period threshold has been crossed
event Period(uint256 _period);
// Redistribution applied on a single eligible account
event Redistribution(address indexed _account, uint256 indexed _period, uint256 _value);
// Temporary event used in development, will be removed on prod
event Debug(bytes32 _foo);
// EIP173
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner); // EIP173
constructor(string memory _name, string memory _symbol, uint8 _decimals, uint256 _taxLevelMinute, uint256 _periodMinutes, address _defaultSinkAddress) public {
// ACL setup
owner = msg.sender;
minter[owner] = true;
// ERC20 setup
name = _name;
symbol = _symbol;
decimals = _decimals;
// Demurrage setup
periodStart = block.timestamp;
periodDuration = _periodMinutes * 60;
demurrageAmount = uint128(ppmDivider * 1000000); // Represents 38 decimal places
demurragePeriod = 1;
taxLevel = _taxLevelMinute; // Represents 38 decimal places
bytes32 initialRedistribution = toRedistribution(0, 1000000, 0, 1);
redistributions.push(initialRedistribution);
// Misc settings
sinkAddress = _defaultSinkAddress;
minimumParticipantSpend = 10 ** uint256(_decimals);
}
// Given address will be allowed to call the mintTo() function
function addMinter(address _minter) public returns (bool) {
require(msg.sender == owner);
minter[_minter] = true;
return true;
}
// Given address will no longer be allowed to call the mintTo() function
function removeMinter(address _minter) public returns (bool) {
require(msg.sender == owner || _minter == msg.sender);
minter[_minter] = false;
return true;
}
/// Implements ERC20
function balanceOf(address _account) public view returns (uint256) {
uint256 baseBalance;
uint256 currentDemurragedAmount;
uint256 periodCount;
baseBalance = baseBalanceOf(_account);
periodCount = actualPeriod() - demurragePeriod;
currentDemurragedAmount = uint128(decayBy(demurrageAmount, periodCount));
return (baseBalance * currentDemurragedAmount) / (ppmDivider * 1000000);
}
/// Balance unmodified by demurrage
function baseBalanceOf(address _account) public view returns (uint256) {
return account[_account];
}
/// Increases base balance for a single account
function increaseBaseBalance(address _account, uint256 _delta) private returns (bool) {
uint256 oldBalance;
uint256 newBalance;
uint256 workAccount;
workAccount = uint256(account[_account]);
if (_delta == 0) {
return false;
}
oldBalance = baseBalanceOf(_account);
account[_account] = oldBalance + _delta;
return true;
}
/// Decreases base balance for a single account
function decreaseBaseBalance(address _account, uint256 _delta) private returns (bool) {
uint256 oldBalance;
uint256 newBalance;
uint256 workAccount;
workAccount = uint256(account[_account]);
if (_delta == 0) {
return false;
}
oldBalance = baseBalanceOf(_account);
require(oldBalance >= _delta, 'ERR_OVERSPEND'); // overspend guard
account[_account] = oldBalance - _delta;
return true;
}
// Creates new tokens out of thin air, and allocates them to the given address
// Triggers tax
function mintTo(address _beneficiary, uint256 _amount) external returns (bool) {
uint256 baseAmount;
require(minter[msg.sender]);
changePeriod();
baseAmount = _amount;
totalSupply += _amount;
increaseBaseBalance(_beneficiary, baseAmount);
emit Mint(msg.sender, _beneficiary, _amount);
saveRedistributionSupply();
return true;
}
// Deserializes the redistribution word
// uint95(unused) | uint20(demurrageModifier) | uint36(participants) | uint72(value) | uint32(period)
function toRedistribution(uint256 _participants, uint256 _demurrageModifierPpm, uint256 _value, uint256 _period) private pure returns(bytes32) {
bytes32 redistribution;
redistribution |= bytes32((_demurrageModifierPpm << shiftRedistributionDemurrage) & maskRedistributionDemurrage);
redistribution |= bytes32((_value << shiftRedistributionValue) & maskRedistributionValue);
redistribution |= bytes32(_period & maskRedistributionPeriod);
return redistribution;
}
// Serializes the demurrage period part of the redistribution word
function toRedistributionPeriod(bytes32 redistribution) public pure returns (uint256) {
return uint256(redistribution) & maskRedistributionPeriod;
}
// Serializes the supply part of the redistribution word
function toRedistributionSupply(bytes32 redistribution) public pure returns (uint256) {
return (uint256(redistribution) & maskRedistributionValue) >> shiftRedistributionValue;
}
// Serializes the number of participants part of the redistribution word
function toRedistributionDemurrageModifier(bytes32 redistribution) public pure returns (uint256) {
return (uint256(redistribution) & maskRedistributionDemurrage) >> shiftRedistributionDemurrage;
}
// Client accessor to the redistributions array length
function redistributionCount() public view returns (uint256) {
return redistributions.length;
}
// Save the current total supply amount to the current redistribution period
function saveRedistributionSupply() private returns (bool) {
uint256 currentRedistribution;
currentRedistribution = uint256(redistributions[redistributions.length-1]);
currentRedistribution &= (~maskRedistributionValue);
currentRedistribution |= (totalSupply << shiftRedistributionValue);
redistributions[redistributions.length-1] = bytes32(currentRedistribution);
return true;
}
// Get the demurrage period of the current block number
function actualPeriod() public view returns (uint128) {
return uint128((block.timestamp - periodStart) / periodDuration + 1);
}
// Add an entered demurrage period to the redistribution array
function checkPeriod() private view returns (bytes32) {
bytes32 lastRedistribution;
uint256 currentPeriod;
lastRedistribution = redistributions[redistributions.length-1];
currentPeriod = this.actualPeriod();
if (currentPeriod <= toRedistributionPeriod(lastRedistribution)) {
return bytes32(0x00);
}
return lastRedistribution;
}
// Returns the amount sent to the sink address
function applyDefaultRedistribution(bytes32 _redistribution) private returns (uint256) {
uint256 redistributionSupply;
uint256 redistributionPeriod;
uint256 unit;
uint256 truncatedResult;
redistributionSupply = toRedistributionSupply(_redistribution);
unit = (redistributionSupply * taxLevel) / 1000000;
truncatedResult = (unit * 1000000) / taxLevel;
if (truncatedResult < redistributionSupply) {
redistributionPeriod = toRedistributionPeriod(_redistribution); // since we reuse period here, can possibly be optimized by passing period instead
}
increaseBaseBalance(sinkAddress, unit / ppmDivider);
return unit;
}
// Calculate and cache the demurrage value corresponding to the (period of the) time of the method call
function applyDemurrage() public returns (bool) {
uint128 epochPeriodCount;
uint128 periodCount;
uint256 lastDemurrageAmount;
uint256 newDemurrageAmount;
epochPeriodCount = actualPeriod();
periodCount = epochPeriodCount - demurragePeriod;
if (periodCount == 0) {
return false;
}
lastDemurrageAmount = demurrageAmount;
demurrageAmount = uint128(decayBy(lastDemurrageAmount, periodCount));
demurragePeriod = epochPeriodCount;
emit Decayed(epochPeriodCount, periodCount, lastDemurrageAmount, demurrageAmount);
return true;
}
// Return timestamp of start of period threshold
function getPeriodTimeDelta(uint256 _periodCount) public view returns (uint256) {
return periodStart + (_periodCount * periodDuration);
}
// Amount of demurrage cycles inbetween the current timestamp and the given target time
function demurrageCycles(uint256 _target) public view returns (uint256) {
return (block.timestamp - _target) / 60;
}
// Recalculate the demurrage modifier for the new period
function changePeriod() public returns (bool) {
bytes32 currentRedistribution;
bytes32 nextRedistribution;
uint256 currentPeriod;
uint256 currentDemurrageAmount;
uint256 nextRedistributionDemurrage;
uint256 demurrageCounts;
uint256 periodTimestamp;
uint256 nextPeriod;
currentRedistribution = checkPeriod();
if (currentRedistribution == bytes32(0x00)) {
return false;
}
currentPeriod = toRedistributionPeriod(currentRedistribution);
nextPeriod = currentPeriod + 1;
periodTimestamp = getPeriodTimeDelta(currentPeriod);
applyDemurrage();
currentDemurrageAmount = demurrageAmount;
demurrageCounts = demurrageCycles(periodTimestamp);
if (demurrageCounts > 0) {
nextRedistributionDemurrage = growBy(currentDemurrageAmount, demurrageCounts) / ppmDivider;
} else {
nextRedistributionDemurrage = currentDemurrageAmount / ppmDivider;
}
nextRedistribution = toRedistribution(0, nextRedistributionDemurrage, totalSupply, nextPeriod);
redistributions.push(nextRedistribution);
applyDefaultRedistribution(currentRedistribution);
emit Period(nextPeriod);
return true;
}
// Reverse a value reduced by demurrage by the given period to its original value
function growBy(uint256 _value, uint256 _period) public view returns (uint256) {
uint256 valueFactor;
uint256 truncatedTaxLevel;
valueFactor = 1000000;
truncatedTaxLevel = taxLevel / ppmDivider;
for (uint256 i = 0; i < _period; i++) {
valueFactor = valueFactor + ((valueFactor * truncatedTaxLevel) / 1000000);
}
return (valueFactor * _value) / 1000000;
}
// Calculate a value reduced by demurrage by the given period
// TODO: higher precision if possible
function decayBy(uint256 _value, uint256 _period) public view returns (uint256) {
uint256 valueFactor;
uint256 truncatedTaxLevel;
valueFactor = 1000000;
truncatedTaxLevel = taxLevel / ppmDivider;
for (uint256 i = 0; i < _period; i++) {
valueFactor = valueFactor - ((valueFactor * truncatedTaxLevel) / 1000000);
}
return (valueFactor * _value) / 1000000;
}
// Inflates the given amount according to the current demurrage modifier
function toBaseAmount(uint256 _value) public view returns (uint256) {
return (_value * ppmDivider * 1000000) / demurrageAmount;
}
// Implements ERC20, triggers tax and/or redistribution
function approve(address _spender, uint256 _value) public returns (bool) {
uint256 baseValue;
changePeriod();
baseValue = toBaseAmount(_value);
allowance[msg.sender][_spender] += baseValue;
emit Approval(msg.sender, _spender, _value);
return true;
}
// Implements ERC20, triggers tax and/or redistribution
function transfer(address _to, uint256 _value) public returns (bool) {
uint256 baseValue;
bool result;
changePeriod();
baseValue = toBaseAmount(_value);
result = transferBase(msg.sender, _to, baseValue);
emit Transfer(msg.sender, _to, _value);
return result;
}
// Implements ERC20, triggers tax and/or redistribution
function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
uint256 baseValue;
bool result;
changePeriod();
baseValue = toBaseAmount(_value);
require(allowance[_from][msg.sender] >= baseValue);
result = transferBase(_from, _to, baseValue);
emit Transfer(_from, _to, _value);
return result;
}
// ERC20 transfer backend for transfer, transferFrom
function transferBase(address _from, address _to, uint256 _value) private returns (bool) {
uint256 period;
decreaseBaseBalance(_from, _value);
increaseBaseBalance(_to, _value);
period = actualPeriod();
return true;
}
// Implements EIP173
function transferOwnership(address _newOwner) public returns (bool) {
require(msg.sender == owner);
newOwner = _newOwner;
}
// Implements OwnedAccepter
function acceptOwnership() public returns (bool) {
address oldOwner;
require(msg.sender == newOwner);
oldOwner = owner;
owner = newOwner;
newOwner = address(0);
emit OwnershipTransferred(oldOwner, owner);
}
// Implements EIP165
function supportsInterface(bytes4 _sum) public pure returns (bool) {
if (_sum == 0xc6bb4b70) { // ERC20
return true;
}
if (_sum == 0x449a52f8) { // Minter
return true;
}
if (_sum == 0x01ffc9a7) { // EIP165
return true;
}
if (_sum == 0x9493f8b2) { // EIP173
return true;
}
if (_sum == 0x37a47be4) { // OwnedAccepter
return true;
}
return false;
}
}