Dynamic base liquidation percentage

implementation/contracts/deposit/DepositUtils.sol

@@ -230,7 +230,7 @@ library DepositUtils {
         }
 
         // This should make a smooth flow from base% to 100%
-        uint256 _basePercentage = TBTCConstants.getAuctionBasePercentage();
+        uint256 _basePercentage = getAuctionBasePercentage(_d);
         uint256 _elapsedPercentage = uint256(100).sub(_basePercentage).mul(_elapsed).div(TBTCConstants.getAuctionDuration());
         uint256 _percentage = _basePercentage.add(_elapsedPercentage);
 
@@ -367,6 +367,17 @@ library DepositUtils {
         _d.lastRequestedDigest = bytes32(0);
     }
 
+
+    /// @notice     Get the starting percentage of the bond at auction.
+    /// @dev        This will return the same value regardless of collateral price.
+    /// @return     The percentage of the InitialCollateralizationPercent that will result
+    ///             in a 100% bond value base auction given perfect collateralization.
+    function getAuctionBasePercentage(Deposit storage _d) internal view returns (uint256) {
+        ITBTCSystem _sys = ITBTCSystem(_d.TBTCSystem);
+        uint256 initialCollateralizedPercent = _sys.getInitialCollateralizedPercent();
+        return (10000 / initialCollateralizedPercent);
+    }
+
     /// @notice     Seize the signer bond from the keep contract.
     /// @dev        we check our balance before and after.
     /// @return     The amount seized in wei.

implementation/contracts/deposit/TBTCConstants.sol

@@ -26,7 +26,6 @@ library TBTCConstants {
     // Liquidation Flow
     uint256 public constant COURTESY_CALL_DURATION = 6 * 60 * 60; // seconds
     uint256 public constant AUCTION_DURATION = 24 * 60 * 60; // seconds
-    uint256 public constant AUCTION_BASE_PERCENTAGE = 90; // percents
     uint256 public constant PERMITTED_FEE_BUMPS = 5; // number of times the fee can be increased
 
     // Getters for easy access
@@ -47,6 +46,5 @@ library TBTCConstants {
 
     function getCourtesyCallTimeout() public pure returns (uint256) { return COURTESY_CALL_DURATION; }
     function getAuctionDuration() public pure returns (uint256) { return AUCTION_DURATION; }
-    function getAuctionBasePercentage() public pure returns (uint256) { return AUCTION_BASE_PERCENTAGE; }
     function getPermittedFeeBumps() public pure returns (uint256) {return PERMITTED_FEE_BUMPS; }
 }

implementation/contracts/interfaces/ITBTCSystem.sol

@@ -14,4 +14,6 @@ interface ITBTCSystem {
     // passthrough requests for the oracle
     function fetchRelayCurrentDifficulty() external view returns (uint256);
     function fetchRelayPreviousDifficulty() external view returns (uint256);
+
+    function getInitialCollateralizedPercent() external view returns (uint128);
 }

implementation/contracts/test/deposit/TestDeposit.sol

@@ -238,4 +238,8 @@ contract TestDeposit is Deposit {
     function pushFundsToKeepGroup(uint256 _ethValue) public returns (bool) {
         return self.pushFundsToKeepGroup(_ethValue);
     }
+
+    function getAuctionBasePercentage() public view returns (uint256) {
+        return self.getAuctionBasePercentage();
+    }
 }

implementation/contracts/test/deposit/TestTBTCConstants.sol

@@ -26,7 +26,6 @@ library TestTBTCConstants {
     // Liquidation Flow
     uint256 public constant COURTESY_CALL_DURATION = 6 * 60 * 60; // seconds
     uint256 public constant AUCTION_DURATION = 24 * 60 * 60; // seconds
-    uint256 public constant AUCTION_BASE_PERCENTAGE = 90; // percents
     uint256 public constant PERMITTED_FEE_BUMPS = 5; // number of times the fee can be increased
 
     function getBeneficiaryRewardDivisor() public pure returns (uint256) { return BENEFICIARY_FEE_DIVISOR; }
@@ -46,6 +45,5 @@ library TestTBTCConstants {
 
     function getCourtesyCallTimeout() public pure returns (uint256) { return COURTESY_CALL_DURATION; }
     function getAuctionDuration() public pure returns (uint256) { return AUCTION_DURATION; }
-    function getAuctionBasePercentage() public pure returns (uint256) { return AUCTION_BASE_PERCENTAGE; }
     function getPermittedFeeBumps() public pure returns (uint256) {return PERMITTED_FEE_BUMPS; }
 }

implementation/test/DepositLiquidationTest.js

@@ -185,7 +185,7 @@ describe("DepositLiquidation", async function() {
       const block = await web3.eth.getBlock("latest")
       const notifiedTime = block.timestamp
       const value = 1000000000000
-      const basePercentage = await tbtcConstants.getAuctionBasePercentage.call()
+      const basePercentage = await testDeposit.getAuctionBasePercentage.call()
 
       await ecdsaKeepStub.pushFundsFromKeep(testDeposit.address, {value: value})
 
@@ -227,7 +227,7 @@ describe("DepositLiquidation", async function() {
       const notifiedTime = block.timestamp
       const liquidationInitiator = accounts[2]
       const value = 1000000000000
-      const basePercentage = await tbtcConstants.getAuctionBasePercentage.call()
+      const basePercentage = await testDeposit.getAuctionBasePercentage.call()
 
       await ecdsaKeepStub.pushFundsFromKeep(testDeposit.address, {value: value})
 

implementation/test/DepositUtilsTest.js

@@ -383,12 +383,24 @@ describe("DepositUtils", async function() {
     })
   })
 
+  describe("getAuctionBasePercentage()", async () => {
+    it("returns correct base percentage", async () => {
+      const basePercentage = await testDeposit.getAuctionBasePercentage.call()
+
+      const initialCollateralization = await tbtcSystemStub.getInitialCollateralizedPercent()
+
+      // 10000 to avoid losing value to truncating is solidity.
+      const expecged = new BN(10000).div(initialCollateralization)
+      expect(basePercentage).to.eq.BN(expecged) // 66 for 150
+    })
+  })
+
   describe("auctionValue()", async () => {
     let duration
     let basePercentage
     before(async () => {
       duration = await tbtcConstants.getAuctionDuration.call()
-      basePercentage = await tbtcConstants.getAuctionBasePercentage.call()
+      basePercentage = await testDeposit.getAuctionBasePercentage.call()
       auctionValue = new BN(100000000)
     })
     beforeEach(async () => {