Bump eth-erc20. add initial single and cap contract adaptations

python/erc20_demurrage_token/token.py

@@ -40,13 +40,13 @@ class DemurrageTokenSettings:
 
 class DemurrageToken(ERC20):
 
-    __abi = None
-    __bytecode = None
+    __abi = {}
+    __bytecode = {}
 
     def constructor(self, sender_address, settings, redistribute=True, cap=0, tx_format=TxFormat.JSONRPC):
-        if not redistribute or cap:
-            raise NotImplementedError('token cap and sink only redistribution not yet implemented')
-        code = DemurrageToken.bytecode()
+        if int(cap) < 0:
+            raise ValueError('cap must be 0 or positive integer')
+        code = DemurrageToken.bytecode(multi=redistribute, cap=cap>0)
         enc = ABIContractEncoder()
         enc.string(settings.name)
         enc.string(settings.symbol)
@@ -64,22 +64,39 @@ class DemurrageToken(ERC20):
     def gas(code=None):
         return 3500000
 
+
     @staticmethod
-    def abi():
-        if DemurrageToken.__abi == None:
-            f = open(os.path.join(data_dir, 'DemurrageTokenMultiNocap.json'), 'r')
-            DemurrageToken.__abi = json.load(f)
-            f.close()
-        return DemurrageToken.__abi
+    def __to_contract_name(multi, cap):
+        name = 'DemurrageToken'
+        if multi:
+            name += 'Multi'
+        else:
+            name += 'Single'
+        if cap:
+            name += 'Cap'
+        else:
+            name += 'Nocap'
+        return name
 
 
     @staticmethod
-    def bytecode():
-        if DemurrageToken.__bytecode == None:
-            f = open(os.path.join(data_dir, 'DemurrageTokenMultiNocap.bin'), 'r')
-            DemurrageToken.__bytecode = f.read()
+    def abi(multi=True, cap=False):
+        name = DemurrageToken.__to_contract_name(multi, cap)
+        if DemurrageToken.__abi.get(name) == None:
+            f = open(os.path.join(data_dir, name + '.json'), 'r')
+            DemurrageToken.__abi[name] = json.load(f)
             f.close()
-        return DemurrageToken.__bytecode
+        return DemurrageToken.__abi[name]
+
+
+    @staticmethod
+    def bytecode(multi=True, cap=False):
+        name = DemurrageToken.__to_contract_name(multi, cap)
+        if DemurrageToken.__bytecode.get(name) == None:
+            f = open(os.path.join(data_dir, name + '.bin'), 'r')
+            DemurrageToken.__bytecode[name] = f.read()
+            f.close()
+        return DemurrageToken.__bytecode[name]
 
 
     def add_minter(self, contract_address, sender_address, address, tx_format=TxFormat.JSONRPC):

python/requirements.txt

@@ -1,3 +1,3 @@
 chainlib~=0.0.3rc3
-eth-erc20~=0.0.9a3
+eth-erc20~=0.0.9a4
 crypto-dev-signer~=0.4.14b3

python/tests/base.py

@@ -35,6 +35,10 @@ class TestDemurrage(EthTesterCase):
 
     def setUp(self):
         super(TestDemurrage, self).setUp()
+
+        self.tax_level = TAX_LEVEL
+        self.period = PERIOD
+
         nonce_oracle = RPCNonceOracle(self.accounts[0], self.rpc)
         self.settings = DemurrageTokenSettings()
         self.settings.name = 'Foo Token'
@@ -64,16 +68,31 @@ class TestDemurrage(EthTesterCase):
 
 class TestDemurrageDefault(TestDemurrage):
 
+    def __deploy(self, interface):
+        self.default_supply = 1000000000000
+        self.supply_cap = self.default_supply * 10
+
+        (tx_hash, o) = interface.constructor(self.accounts[0], self.settings, redistribute=True, cap=0)
+        r = self.rpc.do(o)
+        o = receipt(tx_hash)
+        r = self.rpc.do(o)
+        self.assertEqual(r['status'], 1)
+        self.addresses['MultiNocap'] = r['contract_address']
+
+        (tx_hash, o) = interface.constructor(self.accounts[0], self.settings, redistribute=False, cap=0)
+        r = self.rpc.do(o)
+        o = receipt(tx_hash)
+        r = self.rpc.do(o)
+        self.assertEqual(r['status'], 1)
+        self.addresses['SingleNocap'] = r['contract_address']
+
+
     def setUp(self):
         super(TestDemurrageDefault, self).setUp()
    
         nonce_oracle = RPCNonceOracle(self.accounts[0], self.rpc)
         c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
-        (tx_hash, o) = c.constructor(self.accounts[0], self.settings)
-        r = self.rpc.do(o)
 
-        o = receipt(tx_hash)
-        r = self.rpc.do(o)
-        self.assertEqual(r['status'], 1)
-
-        self.address = r['contract_address']
+        self.addresses = {}
+        self.__deploy(c)
+        self.address = self.addresses['MultiNocap']

python/tests/test_redistribution.py

@@ -26,11 +26,6 @@ logg = logging.getLogger()
 
 testdir = os.path.dirname(__file__)
 
-#BLOCKTIME = 5 # seconds
-TAX_LEVEL = 10000 * 2 # 2%
-#PERIOD = int(60/BLOCKTIME) * 60 * 24 * 30 # month
-PERIOD = 1
-
 
 class TestRedistribution(TestDemurrageDefault):
 
@@ -104,7 +99,7 @@ class TestRedistribution(TestDemurrageDefault):
 
 
     def test_redistribution_balance_on_zero_participants(self):
-        supply = 1000000000000
+        supply = self.default_supply
 
         nonce_oracle = RPCNonceOracle(self.accounts[0], self.rpc)
         c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
@@ -127,7 +122,7 @@ class TestRedistribution(TestDemurrageDefault):
         o = c.total_supply(self.address, sender_address=self.accounts[0])
         r = self.rpc.do(o)
         total_supply = c.parse_total_supply(r)
-        sink_increment = int(total_supply * (TAX_LEVEL / 1000000))
+        sink_increment = int(total_supply * (self.tax_level / 1000000))
         self.assertEqual(supply, total_supply)
 
         for l in rcpt['logs']:
@@ -136,14 +131,14 @@ class TestRedistribution(TestDemurrageDefault):
                 self.assertEqual(period, 2)
                 b = bytes.fromhex(strip_0x(l['data']))
                 remainder = int.from_bytes(b, 'big')
-                self.assertEqual(remainder, int((1000000 - TAX_LEVEL) * (10 ** 32)))
+                self.assertEqual(remainder, int((1000000 - self.tax_level) * (10 ** 32)))
 
         o = c.balance_of(self.address, self.sink_address, sender_address=self.accounts[0])
         r = self.rpc.do(o)
         sink_balance = c.parse_balance_of(r)
 
         self.assertEqual(sink_balance, int(sink_increment * 0.98))
-        self.assertEqual(sink_balance, int(sink_increment * (1000000 - TAX_LEVEL) / 1000000))
+        self.assertEqual(sink_balance, int(sink_increment * (1000000 - self.tax_level) / 1000000))
 
         o = c.balance_of(self.address, self.accounts[1], sender_address=self.accounts[0])
         r = self.rpc.do(o)
@@ -215,14 +210,14 @@ class TestRedistribution(TestDemurrageDefault):
         r = self.rpc.do(o)
         bummer_balance = c.parse_balance_of(r)
 
-        self.assertEqual(bummer_balance, mint_amount - (mint_amount * (TAX_LEVEL / 1000000)))
+        self.assertEqual(bummer_balance, mint_amount - (mint_amount * (self.tax_level / 1000000)))
         logg.debug('bal {} '.format(bummer_balance))
 
         o = c.balance_of(self.address, self.accounts[1], sender_address=self.accounts[0])
         r = self.rpc.do(o)
         bummer_balance = c.parse_balance_of(r)
         spender_balance = mint_amount - spend_amount
-        spender_decayed_balance = int(spender_balance - (spender_balance * (TAX_LEVEL / 1000000)))
+        spender_decayed_balance = int(spender_balance - (spender_balance * (self.tax_level / 1000000)))
         self.assertEqual(bummer_balance, spender_decayed_balance)
         logg.debug('bal {} '.format(bummer_balance))
 
@@ -254,9 +249,9 @@ class TestRedistribution(TestDemurrageDefault):
         actual_period = c.parse_actual_period(r)
         logg.debug('period {}'.format(actual_period))
 
-        redistribution = int((z / 2) * (TAX_LEVEL / 1000000))
+        redistribution = int((z / 2) * (self.tax_level / 1000000))
         spender_new_base_balance = ((mint_amount - spend_amount) + redistribution)
-        spender_new_decayed_balance = int(spender_new_base_balance - (spender_new_base_balance * (TAX_LEVEL / 1000000)))
+        spender_new_decayed_balance = int(spender_new_base_balance - (spender_new_base_balance * (self.tax_level / 1000000)))
 
         o = c.balance_of(self.address, self.accounts[1], sender_address=self.accounts[0])
         r = self.rpc.do(o)

python/tests/test_single.py

@@ -0,0 +1,61 @@
+import os
+import unittest
+import json
+import logging
+
+# external imports
+from chainlib.eth.constant import ZERO_ADDRESS
+from chainlib.eth.nonce import RPCNonceOracle
+from chainlib.eth.tx import receipt
+from chainlib.eth.block import block_latest
+from chainlib.eth.address import to_checksum_address
+from hexathon import (
+        strip_0x,
+        add_0x,
+        )
+
+# local imports
+from erc20_demurrage_token import DemurrageToken
+
+# test imports
+from tests.base import TestDemurrageDefault
+
+logging.basicConfig(level=logging.DEBUG)
+logg = logging.getLogger()
+
+testdir = os.path.dirname(__file__)
+
+
+class TestRedistributionSingle(TestDemurrageDefault):
+
+    def test_single_even_if_multiple(self):
+        nonce_oracle = RPCNonceOracle(self.accounts[0], self.rpc)
+        c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
+
+        (tx_hash, o) = c.mint_to(self.address, self.accounts[0], self.accounts[1], 100000000)
+        r = self.rpc.do(o)
+
+        external_address = to_checksum_address('0x' + os.urandom(20).hex())
+        nonce_oracle = RPCNonceOracle(self.accounts[2], self.rpc)
+        c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
+        (tx_hash, o) = c.transfer(self.address, self.accounts[1], external_address, 10000000)
+        r = self.rpc.do(o)
+
+        nonce_oracle = RPCNonceOracle(self.accounts[3], self.rpc)
+        c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
+        (tx_hash, o) = c.transfer(self.address, self.accounts[2], external_address, 20000000)
+        r = self.rpc.do(o)
+
+        self.backend.time_travel(self.start_time + 61)
+        (tx_hash, o) = c.apply_demurrage(self.address, self.accounts[0])
+        self.rpc.do(o)
+        o = receipt(tx_hash)
+        rcpt = self.rpc.do(o)
+        self.assertEqual(rcpt['status'], 1)
+
+        (tx_hash, o) = c.change_period(self.address, self.accounts[0])
+        self.rpc.do(o)
+        o = receipt(tx_hash)
+        r = self.rpc.do(o)
+        self.assertEqual(r['status'], 1)
+

solidity/DemurrageTokenMultiCap.sol

@@ -0,0 +1,616 @@
+pragma solidity > 0.6.11;
+
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+contract DemurrageTokenMultiCap {
+
+	// Redistribution bit field, with associated shifts and masks
+	// (Uses sub-byte boundaries)
+	bytes32[] public redistributions; // uint1(isFractional) | 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 shiftRedistributionParticipants	= 104;
+	uint256 constant maskRedistributionParticipants	= 0x00000000000000000000000000000fffffffff00000000000000000000000000; // ((1 << 36) - 1) << 104
+	uint8 constant shiftRedistributionDemurrage	= 140;
+	uint256 constant maskRedistributionDemurrage	= 0x000000000000000000000000fffff00000000000000000000000000000000000; // ((1 << 20) - 1) << 140
+	uint8 constant shiftRedistributionIsFractional	= 255;
+	uint256 constant maskRedistributionIsFractional	= 0x8000000000000000000000000000000000000000000000000000000000000000; // 1 << 255
+
+	// Account bit field, with associated shifts and masks
+	// Mirrors structure of redistributions for consistency
+	mapping (address => bytes32) account; // uint152(unused) | uint32(period) | uint72(value)
+	uint8 constant shiftAccountValue		= 0;
+	uint256 constant maskAccountValue 		= 0x0000000000000000000000000000000000000000000000ffffffffffffffffff; // (1 << 72) - 1
+	uint8 constant shiftAccountPeriod		= 72;
+	uint256 constant maskAccountPeriod 		= 0x00000000000000000000000000000000000000ffffffff000000000000000000; // ((1 << 32) - 1) << 72
+
+	// 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;
+
+	// Maximum amount of tokens that can be minted
+	uint256 public supplyCap;
+
+	// 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 uint256 _supplyCap) 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
+		supplyCap = supplyCap;
+		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 uint256(account[_account]) & maskAccountValue;
+	}
+
+	/// 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);
+		newBalance = oldBalance + _delta;
+		require(uint160(newBalance) > uint160(oldBalance), 'ERR_WOULDWRAP'); // revert if increase would result in a wrapped value
+		workAccount &= (~maskAccountValue); 
+		workAccount |= (newBalance & maskAccountValue);
+		account[_account] = bytes32(workAccount);
+		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
+		newBalance = oldBalance - _delta;
+		workAccount &= (~maskAccountValue);
+		workAccount |= (newBalance & maskAccountValue);
+		account[_account] = bytes32(workAccount);
+		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]);
+		require(_amount + totalSupply <= supplyCap);
+
+		changePeriod();
+		baseAmount = _amount;
+		totalSupply += _amount;
+		increaseBaseBalance(_beneficiary, baseAmount);
+		emit Mint(msg.sender, _beneficiary, _amount);
+		saveRedistributionSupply();
+		return true;
+	}
+
+	// Deserializes the redistribution word
+	// uint1(isFractional) | 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((_participants << shiftRedistributionParticipants) & maskRedistributionParticipants);
+		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 toRedistributionParticipants(bytes32 redistribution) public pure returns (uint256) {
+		return (uint256(redistribution) & maskRedistributionParticipants) >> shiftRedistributionParticipants;
+	}
+
+	// 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;
+	}
+
+	// Add number of participants for the current redistribution period by one
+	function incrementRedistributionParticipants() private returns (bool) {
+		bytes32 currentRedistribution;
+		uint256 tmpRedistribution;
+		uint256 participants;
+
+		currentRedistribution = redistributions[redistributions.length-1];
+		participants = toRedistributionParticipants(currentRedistribution) + 1;
+		tmpRedistribution = uint256(currentRedistribution);
+		tmpRedistribution &= (~maskRedistributionParticipants);
+		tmpRedistribution |= ((participants << shiftRedistributionParticipants) & maskRedistributionParticipants);
+
+		redistributions[redistributions.length-1] = bytes32(tmpRedistribution);
+
+		return true;
+	}
+
+	// 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;
+	}
+
+	// Deserialize the pemurrage period for the given account is participating in
+	function accountPeriod(address _account) public view returns (uint256) {
+		return (uint256(account[_account]) & maskAccountPeriod) >> shiftAccountPeriod;
+	}
+
+	// Save the given demurrage period as the currently participation period for the given address
+	function registerAccountPeriod(address _account, uint256 _period) private returns (bool) {
+		account[_account] &= bytes32(~maskAccountPeriod);
+		account[_account] |= bytes32((_period << shiftAccountPeriod) & maskAccountPeriod);
+		incrementRedistributionParticipants();
+		return true;
+	}
+
+	// Determine whether the unit number is rounded down, rounded up or evenly divides.
+	// Returns 0 if evenly distributed, or the remainder as a positive number
+	// A _numParts value 0 will be interpreted as the value 1
+	function remainder(uint256 _numParts, uint256 _sumWhole) public pure returns (uint256) {
+		uint256 unit;
+		uint256 truncatedResult;
+
+		if (_numParts == 0) { // no division by zero please
+			revert('ERR_NUMPARTS_ZERO');
+		}
+		require(_numParts < _sumWhole); // At least you are never LESS than the sum of your parts. Think about that.
+
+		unit = _sumWhole / _numParts;
+		truncatedResult = unit * _numParts;
+		return _sumWhole - truncatedResult;
+	}
+
+	// Called in the edge case where participant number is 0. It will override the participant count to 1.
+	// Returns the remainder 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
+			redistributions[redistributionPeriod-1] &= bytes32(~maskRedistributionParticipants); // just to be safe, zero out all participant count data, in this case there will be only one
+			redistributions[redistributionPeriod-1] |= bytes32(maskRedistributionIsFractional | (1 << shiftRedistributionParticipants));
+		}
+
+		increaseBaseBalance(sinkAddress, unit / ppmDivider);
+		return unit;
+	}
+
+	// sets the remainder bit for the given period and books the remainder to the sink address balance
+	// returns false if no change was made
+	function applyRemainderOnPeriod(uint256 _remainder, uint256 _period) private returns (bool) {
+		uint256 periodSupply;
+
+		if (_remainder == 0) {
+			return false;
+		}
+
+		// TODO: is this needed?
+		redistributions[_period-1] |= bytes32(maskRedistributionIsFractional);
+
+		periodSupply = toRedistributionSupply(redistributions[_period-1]);
+		increaseBaseBalance(sinkAddress, periodSupply - _remainder);
+		return true;
+	}
+
+
+	// 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
+	// After this, all REPORTED balances will have been reduced by the corresponding ratio (but the effecive totalsupply stays the same)
+	function changePeriod() public returns (bool) {
+		bytes32 currentRedistribution;
+		bytes32 nextRedistribution;
+		uint256 currentPeriod;
+		uint256 currentParticipants;
+		uint256 currentRemainder;
+		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);
+
+		currentParticipants = toRedistributionParticipants(currentRedistribution);
+		if (currentParticipants == 0) {
+			currentRemainder = applyDefaultRedistribution(currentRedistribution);
+		} else {
+			currentRemainder = remainder(currentParticipants, totalSupply); // we can use totalSupply directly because it will always be the same as the recorded supply on the current redistribution
+			applyRemainderOnPeriod(currentRemainder, currentPeriod);
+		}
+		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;
+	}
+
+	// If the given account is participating in a period and that period has been crossed
+	// THEN increase the base value of the account with its share of the value reduction of the period
+	function applyRedistributionOnAccount(address _account) public returns (bool) {
+		bytes32 periodRedistribution;
+		uint256 supply;
+		uint256 participants;
+		uint256 baseValue;
+		uint256 value;
+		uint256 period;
+		uint256 demurrage;
+	       
+		period = accountPeriod(_account);
+		if (period == 0 || period >= actualPeriod()) {
+			return false;
+		}
+		periodRedistribution = redistributions[period-1];
+		participants = toRedistributionParticipants(periodRedistribution);
+		if (participants == 0) {
+			return false;
+		}
+
+		supply = toRedistributionSupply(periodRedistribution);
+		demurrage = toRedistributionDemurrageModifier(periodRedistribution);
+		baseValue = ((supply / participants) * (taxLevel / 1000000)) / ppmDivider;
+		value = (baseValue * demurrage) / 1000000;
+
+		// zero out period for the account
+		account[_account] &= bytes32(~maskAccountPeriod); 
+		increaseBaseBalance(_account, value);
+
+		emit Redistribution(_account, period, value);
+		return true;
+	}
+
+	// Inflates the given amount according to the current demurrage modifier
+	function toBaseAmount(uint256 _value) public view returns (uint256) {
+		//return (_value * ppmDivider * 1000000) / toDemurrageAmount(demurrageModifier);
+		return (_value * ppmDivider * 1000000) / demurrageAmount;
+	}
+
+	// Implements ERC20, triggers tax and/or redistribution
+	function approve(address _spender, uint256 _value) public returns (bool) {
+		uint256 baseValue;
+
+		changePeriod();
+		applyRedistributionOnAccount(msg.sender);
+
+		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();
+		applyRedistributionOnAccount(msg.sender);
+
+		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();
+		applyRedistributionOnAccount(msg.sender);
+
+		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();
+		if (_value >= minimumParticipantSpend && accountPeriod(_from) != period && _from != _to) {
+			registerAccountPeriod(_from, period);
+		}
+		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;
+	}
+}

solidity/DemurrageTokenMultiNocap.sol

@@ -2,7 +2,7 @@ pragma solidity > 0.6.11;
 
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-contract RedistributedDemurrageToken {
+contract DemurrageTokenMultiNocap {
 
 	// Redistribution bit field, with associated shifts and masks
 	// (Uses sub-byte boundaries)

solidity/DemurrageTokenSingleNocap.sol

@@ -0,0 +1,609 @@
+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; // uint1(isFractional) | 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 shiftRedistributionParticipants	= 104;
+	uint256 constant maskRedistributionParticipants	= 0x00000000000000000000000000000fffffffff00000000000000000000000000; // ((1 << 36) - 1) << 104
+	uint8 constant shiftRedistributionDemurrage	= 140;
+	uint256 constant maskRedistributionDemurrage	= 0x000000000000000000000000fffff00000000000000000000000000000000000; // ((1 << 20) - 1) << 140
+	uint8 constant shiftRedistributionIsFractional	= 255;
+	uint256 constant maskRedistributionIsFractional	= 0x8000000000000000000000000000000000000000000000000000000000000000; // 1 << 255
+
+	// Account bit field, with associated shifts and masks
+	// Mirrors structure of redistributions for consistency
+	mapping (address => bytes32) account; // uint152(unused) | uint32(period) | uint72(value)
+	uint8 constant shiftAccountValue		= 0;
+	uint256 constant maskAccountValue 		= 0x0000000000000000000000000000000000000000000000ffffffffffffffffff; // (1 << 72) - 1
+	uint8 constant shiftAccountPeriod		= 72;
+	uint256 constant maskAccountPeriod 		= 0x00000000000000000000000000000000000000ffffffff000000000000000000; // ((1 << 32) - 1) << 72
+	
+	// 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 uint256(account[_account]) & maskAccountValue;
+		//return uint256(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);
+		newBalance = oldBalance + _delta;
+		require(uint160(newBalance) > uint160(oldBalance), 'ERR_WOULDWRAP'); // revert if increase would result in a wrapped value
+		workAccount &= (~maskAccountValue); 
+		workAccount |= (newBalance & maskAccountValue);
+		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
+		newBalance = oldBalance - _delta;
+		workAccount &= (~maskAccountValue);
+		workAccount |= (newBalance & maskAccountValue);
+		account[_account] = bytes32(workAccount);
+		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
+	// uint1(isFractional) | 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((_participants << shiftRedistributionParticipants) & maskRedistributionParticipants);
+		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 toRedistributionParticipants(bytes32 redistribution) public pure returns (uint256) {
+		return (uint256(redistribution) & maskRedistributionParticipants) >> shiftRedistributionParticipants;
+	}
+
+	// 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;
+	}
+
+	// Add number of participants for the current redistribution period by one
+	function incrementRedistributionParticipants() private returns (bool) {
+		bytes32 currentRedistribution;
+		uint256 tmpRedistribution;
+		uint256 participants;
+
+		currentRedistribution = redistributions[redistributions.length-1];
+		participants = toRedistributionParticipants(currentRedistribution) + 1;
+		tmpRedistribution = uint256(currentRedistribution);
+		tmpRedistribution &= (~maskRedistributionParticipants);
+		tmpRedistribution |= ((participants << shiftRedistributionParticipants) & maskRedistributionParticipants);
+
+		redistributions[redistributions.length-1] = bytes32(tmpRedistribution);
+
+		return true;
+	}
+
+	// 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;
+	}
+
+	// Deserialize the pemurrage period for the given account is participating in
+	function accountPeriod(address _account) public view returns (uint256) {
+		return (uint256(account[_account]) & maskAccountPeriod) >> shiftAccountPeriod;
+	}
+
+	// Save the given demurrage period as the currently participation period for the given address
+	function registerAccountPeriod(address _account, uint256 _period) private returns (bool) {
+		account[_account] &= bytes32(~maskAccountPeriod);
+		account[_account] |= bytes32((_period << shiftAccountPeriod) & maskAccountPeriod);
+		incrementRedistributionParticipants();
+		return true;
+	}
+
+	// Determine whether the unit number is rounded down, rounded up or evenly divides.
+	// Returns 0 if evenly distributed, or the remainder as a positive number
+	// A _numParts value 0 will be interpreted as the value 1
+	function remainder(uint256 _numParts, uint256 _sumWhole) public pure returns (uint256) {
+		uint256 unit;
+		uint256 truncatedResult;
+
+		if (_numParts == 0) { // no division by zero please
+			revert('ERR_NUMPARTS_ZERO');
+		}
+		require(_numParts < _sumWhole); // At least you are never LESS than the sum of your parts. Think about that.
+
+		unit = _sumWhole / _numParts;
+		truncatedResult = unit * _numParts;
+		return _sumWhole - truncatedResult;
+	}
+
+	// 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
+			redistributions[redistributionPeriod-1] &= bytes32(~maskRedistributionParticipants); // just to be safe, zero out all participant count data, in this case there will be only one
+			redistributions[redistributionPeriod-1] |= bytes32(maskRedistributionIsFractional | (1 << shiftRedistributionParticipants));
+		}
+
+		increaseBaseBalance(sinkAddress, unit / ppmDivider);
+		return unit;
+	}
+
+	// sets the remainder bit for the given period and books the remainder to the sink address balance
+	// returns false if no change was made
+	function applyRemainderOnPeriod(uint256 _remainder, uint256 _period) private returns (bool) {
+		uint256 periodSupply;
+
+		if (_remainder == 0) {
+			return false;
+		}
+
+		// TODO: is this needed?
+		redistributions[_period-1] |= bytes32(maskRedistributionIsFractional);
+
+		periodSupply = toRedistributionSupply(redistributions[_period-1]);
+		increaseBaseBalance(sinkAddress, periodSupply - _remainder);
+		return true;
+	}
+
+
+	// 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 currentParticipants;
+		uint256 currentRemainder;
+		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);
+
+		//currentParticipants = toRedistributionParticipants(currentRedistribution);
+		//if (currentParticipants == 0) {
+		currentRemainder = applyDefaultRedistribution(currentRedistribution);
+		//} else {
+		//	currentRemainder = remainder(currentParticipants, totalSupply); // we can use totalSupply directly because it will always be the same as the recorded supply on the current redistribution
+		//	applyRemainderOnPeriod(currentRemainder, currentPeriod);
+		//}
+		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;
+	}
+
+	// If the given account is participating in a period and that period has been crossed
+	// THEN increase the base value of the account with its share of the value reduction of the period
+	function applyRedistributionOnAccount(address _account) public returns (bool) {
+//		bytes32 periodRedistribution;
+//		uint256 supply;
+//		uint256 participants;
+//		uint256 baseValue;
+//		uint256 value;
+		uint256 period;
+//		uint256 demurrage;
+//	       
+		period = accountPeriod(_account);
+		if (period == 0 || period >= actualPeriod()) {
+			return false;
+		}
+//		periodRedistribution = redistributions[period-1];
+//		participants = toRedistributionParticipants(periodRedistribution);
+//		if (participants == 0) {
+//			return false;
+//		}
+//
+//		supply = toRedistributionSupply(periodRedistribution);
+//		demurrage = toRedistributionDemurrageModifier(periodRedistribution);
+//		baseValue = ((supply / participants) * (taxLevel / 1000000)) / ppmDivider;
+//		value = (baseValue * demurrage) / 1000000;
+//
+//		// zero out period for the account
+		account[_account] &= bytes32(~maskAccountPeriod); 
+//		increaseBaseBalance(_account, value);
+//
+//		emit Redistribution(_account, period, value);
+		return true;
+	}
+
+	// Inflates the given amount according to the current demurrage modifier
+	function toBaseAmount(uint256 _value) public view returns (uint256) {
+		//return (_value * ppmDivider * 1000000) / toDemurrageAmount(demurrageModifier);
+		return (_value * ppmDivider * 1000000) / demurrageAmount;
+	}
+
+	// Implements ERC20, triggers tax and/or redistribution
+	function approve(address _spender, uint256 _value) public returns (bool) {
+		uint256 baseValue;
+
+		changePeriod();
+		//applyRedistributionOnAccount(msg.sender);
+
+		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();
+		//applyRedistributionOnAccount(msg.sender);
+
+		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();
+		//applyRedistributionOnAccount(msg.sender);
+
+		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();
+		if (_value >= minimumParticipantSpend && accountPeriod(_from) != period && _from != _to) {
+			registerAccountPeriod(_from, period);
+		}
+		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;
+	}
+}

solidity/Makefile

@@ -1,16 +1,32 @@
 SOLC = /usr/bin/solc
 
-all:
+all: multi_nocap multi_cap single_nocap
+
+
+multi_nocap:
 	$(SOLC) DemurrageTokenMultiNocap.sol --abi --evm-version byzantium | awk 'NR>3' > DemurrageTokenMultiNocap.json
 	$(SOLC) DemurrageTokenMultiNocap.sol --bin --evm-version byzantium | awk 'NR>3' > DemurrageTokenMultiNocap.bin
+	truncate -s -1 DemurrageTokenMultiCap.bin
+
+multi_cap:
+	$(SOLC) DemurrageTokenMultiCap.sol --abi --evm-version byzantium | awk 'NR>3' > DemurrageTokenMultiCap.json
+	$(SOLC) DemurrageTokenMultiCap.sol --bin --evm-version byzantium | awk 'NR>3' > DemurrageTokenMultiCap.bin
 	truncate -s -1 DemurrageTokenMultiNocap.bin
 
+multi: multi_nocap multi_cap
+
+single_nocap:
+	$(SOLC) DemurrageTokenSingleNocap.sol --abi --evm-version byzantium | awk 'NR>3' > DemurrageTokenSingleNocap.json
+	$(SOLC) DemurrageTokenSingleNocap.sol --bin --evm-version byzantium | awk 'NR>3' > DemurrageTokenSingleNocap.bin
+	truncate -s -1 DemurrageTokenSingleNocap.bin
+
 test: all
 	python ../python/tests/test_basic.py
 	python ../python/tests/test_period.py
 	python ../python/tests/test_redistribution.py
+	python ../python/tests/test_pure.py
 
 install: all
-	cp -v DemurrageTokenMultiNocap.{json,bin} ../python/sarafu_token/data/
+	cp -v DemurrageToken*.{json,bin} ../python/erc20_demurrage_token/data/
 	
 .PHONY: test install