WIP implement full history of account balance snapshot

solidity/DemurrageTokenSingleNocap.sol

@@ -14,7 +14,13 @@ contract DemurrageTokenSingleCap {
 	uint256 constant maskRedistributionDemurrage	= 0x0000000000ffffffffffffffffffffffffffff00000000000000000000000000; // ((1 << 36) - 1) << 140
 
 	// Account balances
-	mapping (address => uint256) account;
+	mapping (address => bytes32[] ) account;
+	uint8 constant shiftAccountValue		= 0;
+	uint256 constant maskAccountValue 		= 0x0000000000000000000000000000000000000000000000ffffffffffffffffff; // (1 << 72) - 1
+	uint8 constant shiftAccountPeriod		= 72;
+	uint256 constant maskAccountPeriod 		= 0x00000000000000000000000000000000000000ffffffff000000000000000000; // ((1 << 32) - 1) << 72
+	uint8 constant shiftAccountUsed			= 255;
+	uint256 constant maskAccountUsed 		= 0x8000000000000000000000000000000000000000000000000000000000000000; // (1 << 255)
 	
 	// Cached demurrage amount, ppm with 38 digit resolution
 	uint128 public demurrageAmount;
@@ -163,43 +169,36 @@ contract DemurrageTokenSingleCap {
 		return (baseBalance * currentDemurragedAmount) / (nanoDivider * 1000000000000);
 	}
 
+
 	/// Balance unmodified by demurrage
 	function baseBalanceOf(address _account) public view returns (uint256) {
-		return account[_account];
+		uint256 lastPeriodUsed;
+
+		lastPeriodUsed = account[_account].length;
+		if (lastPeriodUsed == 0) {
+			return 0;
 		}
+		return uint256(account[_account][lastPeriodUsed]) & 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);
-		account[_account] = oldBalance + _delta;
+		movePeriodBalance(_account, int256(_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;
+		movePeriodBalance(_account, int256(_delta) * -1);
 		return true;
 	}
 
@@ -354,6 +353,54 @@ contract DemurrageTokenSingleCap {
 		return (block.timestamp - _target) / 60;
 	}
 
+
+	// Deserialize the pemurrage period for the given account is participating in
+	function accountPeriod(address _account) public view returns (uint256) {
+		uint256 accountPeriods;
+
+		accountPeriods = account[_account].length;
+		if (accountPeriods == 0) {
+			return 0;
+		}
+		return accountPeriodBase(_account, accountPeriods - 1);
+	}
+
+	function accountPeriodBase(address _account, uint256 _idx) private view returns (uint256) {
+		return (uint256(account[_account][_idx]) & maskAccountPeriod) >> shiftAccountPeriod;
+	}
+
+	function movePeriodBalance(address _account, int256 _delta) private {
+		int256 oldBalance;
+		uint256 newBalance;
+		uint256 workAccount;
+
+		//workAccount = uint256(account[_index][_account]);
+
+		oldBalance = int256(baseBalanceOf(_account));
+		newBalance = uint256(oldBalance + _delta);
+		require(uint72(newBalance) > uint72(uint256(oldBalance)), 'ERR_WOULDWRAP'); // revert if increase would result in a wrapped value
+		workAccount = (1 << 255);
+
+		workAccount |= ((uint32(lastPeriod) << shiftAccountPeriod) & maskAccountPeriod);
+		workAccount |= (baseBalanceOf(_account) & maskAccountValue);
+		account[_account].push(bytes32(workAccount));
+	}
+
+	function registerAccountPeriod(address _account, int256 _delta) public {
+		uint256 accountPeriods;
+		uint256 lastPeriodUsed;
+
+		accountPeriods = account[_account].length;
+		if (lastPeriodUsed == 0) {
+			account[_account].push(bytes32(uint256(_delta) | (1 << 255)));
+			return;
+		}
+		lastPeriodUsed = accountPeriodBase(_account, accountPeriods - 1);
+		if (lastPeriodUsed != lastPeriod) {
+			movePeriodBalance(_account, _delta);
+		}
+	}
+
 	// Recalculate the demurrage modifier for the new period
 	// Note that the supply for the consecutive period will be taken at the time of code execution, and thus not necessarily at the time when the redistribution period threshold was crossed.
 	function changePeriod() public returns (bool) {
@@ -525,7 +572,7 @@ contract DemurrageTokenSingleCap {
 	// Only token minters can burn tokens
 	function burn(uint256 _value) public {
 		require(minter[msg.sender]);
-		require(_value <= account[msg.sender]);
+		require(_value <= balanceOf(msg.sender));
 		uint256 _delta = toBaseAmount(_value);
 
 		applyDemurrage();