Remove the updateTime retval from Oracle.latestPrice(): saves gas and we don't use it anymore.

jacob-eliosoff · jacob-eliosoff · commit 8841e02be2f6 · 2021-10-08T19:08:39.000-04:00
diff --git a/contracts/USM.sol b/contracts/USM.sol
@@ -179,7 +179,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
         require(ls.ethPool > 0, "Fund before minting");
 
         // 3. Refresh the oracle price (if available - see checkForFreshOraclePrice() below):
-        (ls.ethUsdPrice,, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
+        (ls.ethUsdPrice, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
 
         // 4. Calculate usmOut:
         uint adjShrinkFactor;
@@ -201,7 +201,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
         LoadedState memory ls = loadState();
 
         // 2. Refresh the oracle price:
-        (ls.ethUsdPrice,, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
+        (ls.ethUsdPrice, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
 
         // 3. Calculate ethOut:
         uint adjGrowthFactor;
@@ -225,7 +225,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
         ls.ethPool -= msg.value;    // Backing out the ETH just received, which our calculations should ignore
 
         // 2. Refresh the oracle price:
-        (ls.ethUsdPrice,, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
+        (ls.ethUsdPrice, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
 
         // 3. Refresh timeSystemWentUnderwater, and replace ls.usmTotalSupply with the *effective* USM supply for FUM buys:
         uint debtRatio_;
@@ -253,7 +253,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
         LoadedState memory ls = loadState();
 
         // 2. Refresh the oracle price:
-        (ls.ethUsdPrice,, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
+        (ls.ethUsdPrice, ls.bidAskAdjustment) = checkForFreshOraclePrice(ls);
 
         // 3. Calculate ethOut:
         uint fumSupply = fum.totalSupply();
@@ -276,10 +276,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
     }
 
     /**
-     * @notice Stores the current price, `bidAskAdjustment`, and `timeSystemWentUnderwater`.  Note that whereas most calls to
-     * this function store a fresh `bidAskAdjustmentTimestamp`, most calls do *not* store a fresh `ethUsdPriceTimestamp`: the
-     * latter isn't updated every time this is called with a new price, but only when the *oracle's* price is refreshed.  The
-     * oracle price being "refreshed" is itself a subtle idea: see the comment in `Oracle.latestPrice()`.
+     * @notice Stores the current price (and oracle price), `bidAskAdjustment`, and `timeSystemWentUnderwater`.
      */
     function _storeState(LoadedState memory ls) internal {
         require(ls.bidAskAdjustmentTimestamp <= type(uint32).max, "bidAskAdjustmentTimestamp overflow");
@@ -322,8 +319,8 @@ contract USM is IUSM, ERC20Permit, OptOutable {
 
     // ____________________ Public Oracle view functions ____________________
 
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
-        (price, updateTime,) = checkForFreshOraclePrice(loadState());
+    function latestPrice() public virtual override view returns (uint price) {
+        (price,) = checkForFreshOraclePrice(loadState());
     }
 
     // ____________________ Public informational view functions ____________________
@@ -332,16 +329,11 @@ contract USM is IUSM, ERC20Permit, OptOutable {
      * @notice Checks the external oracle for a fresh ETH/USD price.  If it has one, we take it as the new USM system price
      * (and update `bidAskAdjustment` as described below); if no fresh oracle price is available, we stick with our existing
      * system price, `ls.ethUsdPrice`, which may have been nudged around by mint/burn operations since the last oracle update.
-     *
-     * Note that our definition of whether an oracle price is "fresh" (`updateTime > ls.ethUsdPriceTimestamp`) isn't as simple
-     * as "whether it's changed since our last call."  Eg, we only consider a Uniswap TWAP price "fresh" when a new price
-     * observation (trade) occurs, even though `price` may change without such an observation.  See the comment in
-     * `Oracle.latestPrice()`.
      */
     function checkForFreshOraclePrice(LoadedState memory ls)
-        public view returns (uint price, uint updateTime, uint adjustment)
+        public view returns (uint price, uint adjustment)
     {
-        (price, updateTime) = oracle.latestPrice();
+        price = oracle.latestPrice();
         uint oraclePriceRounded = price + HALF_TRILLION;    // Round for comparison below (we only store millionths precision)
         unchecked { oraclePriceRounded = oraclePriceRounded / TRILLION * TRILLION; }    // Zeroing out the last 12 digits
 
@@ -358,7 +350,7 @@ contract USM is IUSM, ERC20Permit, OptOutable {
              *
              * 1. storedPrice = $1,000, and bidAskAdjustment = 1.02.  So, our current ETH buy price is $1,020, and our current
              *    ETH sell price is $1,000 (mid).
-             * 2. The oracle comes back with a fresh price (newer updateTime) of $990.
+             * 2. The oracle comes back with a fresh price of $990.
              * 3. The currently adjusted price is buy price (ie, adj > 1).  So, we want to:
              *    a) Update storedPrice (mid) to $990.
              *    b) Update bidAskAdj to ensure that buy price remains >= $1,020.
diff --git a/contracts/USMView.sol b/contracts/USMView.sol
@@ -22,8 +22,7 @@ contract USMView {
      * @return buffer ETH buffer
      */
     function ethBuffer(bool roundUp) external view returns (int buffer) {
-        (uint price, ) = usm.latestPrice();
-        buffer = usm.ethBuffer(price, usm.ethPool(), usm.totalSupply(), roundUp);
+        buffer = usm.ethBuffer(usm.latestPrice(), usm.ethPool(), usm.totalSupply(), roundUp);
     }
 
     /**
@@ -32,8 +31,7 @@ contract USMView {
      * @return usmOut The amount of USM
      */
     function ethToUsm(uint ethAmount, bool roundUp) external view returns (uint usmOut) {
-        (uint price, ) = usm.latestPrice();
-        usmOut = usm.ethToUsm(price, ethAmount, roundUp);
+        usmOut = usm.ethToUsm(usm.latestPrice(), ethAmount, roundUp);
     }
 
     /**
@@ -42,27 +40,24 @@ contract USMView {
      * @return ethOut The amount of ETH
      */
     function usmToEth(uint usmAmount, bool roundUp) external view returns (uint ethOut) {
-        (uint price, ) = usm.latestPrice();
-        ethOut = usm.usmToEth(price, usmAmount, roundUp);
+        ethOut = usm.usmToEth(usm.latestPrice(), usmAmount, roundUp);
     }
 
     /**
      * @notice Calculate debt ratio.
      * @return ratio Debt ratio
      */
     function debtRatio() external view returns (uint ratio) {
-        (uint price, ) = usm.latestPrice();
-        ratio = usm.debtRatio(price, usm.ethPool(), usm.totalSupply());
+        ratio = usm.debtRatio(usm.latestPrice(), usm.ethPool(), usm.totalSupply());
     }
 
     /**
      * @notice Calculate the *marginal* price of USM (in ETH terms) - that is, of the next unit, before price start sliding.
      * @return price USM price in ETH terms
      */
     function usmPrice(IUSM.Side side) external view returns (uint price) {
-        (uint ethUsdPrice, ) = usm.latestPrice();
         IUSM.Side ethSide = (side == IUSM.Side.Buy ? IUSM.Side.Sell : IUSM.Side.Buy);   // Buying USM = selling ETH
-        uint adjustedPrice = usm.adjustedEthUsdPrice(ethSide, ethUsdPrice, usm.bidAskAdjustment());
+        uint adjustedPrice = usm.adjustedEthUsdPrice(ethSide, usm.latestPrice(), usm.bidAskAdjustment());
         price = usm.usmPrice(side, adjustedPrice);
     }
 
@@ -81,7 +76,7 @@ contract USMView {
      * @return price FUM price in ETH terms
      */
     function fumPrice(IUSM.Side side, bool prefund) public view returns (uint price) {
-        (uint ethUsdPrice, ) = usm.latestPrice();
+        uint ethUsdPrice = usm.latestPrice();
         uint adjustedPrice = usm.adjustedEthUsdPrice(side, ethUsdPrice, usm.bidAskAdjustment());
         uint ethPool = usm.ethPool();
         uint usmSupply = usm.totalSupply();
diff --git a/contracts/fuzzing/WETH9Fuzzing.sol b/contracts/fuzzing/WETH9Fuzzing.sol
@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 pragma solidity ^0.8.0;
 import "../mocks/MockWETH9.sol";
-import "hardhat/console.sol";
 
 contract WETH9Fuzzing {
 
diff --git a/contracts/mocks/GasMeasuredOracleWrapper.sol b/contracts/mocks/GasMeasuredOracleWrapper.sol
@@ -14,9 +14,9 @@ contract GasMeasuredOracleWrapper is Oracle {
         oracleName = name;
     }
 
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
+    function latestPrice() public virtual override view returns (uint price) {
         uint gasStart = gasleft();
-        (price, updateTime) = measuredOracle.latestPrice();
+        price = measuredOracle.latestPrice();
         uint gasEnd = gasleft();
         console.log("        ", oracleName, "oracle.latestPrice() cost: ", gasStart - gasEnd);
     }
diff --git a/contracts/mocks/MockChainlinkOracle.sol b/contracts/mocks/MockChainlinkOracle.sol
@@ -12,7 +12,7 @@ import "../oracles/ChainlinkOracle.sol";
 contract MockChainlinkOracle is ChainlinkOracle, SettableOracle {
     constructor(AggregatorV3Interface aggregator_) ChainlinkOracle(aggregator_) {}
 
-    function latestPrice() public override(ChainlinkOracle, Oracle) view returns (uint price, uint updateTime) {
-        (price, updateTime) = (savedPrice != 0) ? (savedPrice, savedUpdateTime) : super.latestPrice();
+    function latestPrice() public override(ChainlinkOracle, Oracle) view returns (uint price) {
+        price = (savedPrice != 0) ? savedPrice : super.latestPrice();
     }
 }
diff --git a/contracts/mocks/MockMedianOracle.sol b/contracts/mocks/MockMedianOracle.sol
@@ -19,7 +19,7 @@ contract MockMedianOracle is MedianOracle, SettableOracle {
             uniswapPool1, uniswapTokenToPrice1, uniswapDecimals1,
             uniswapPool2, uniswapTokenToPrice2, uniswapDecimals2) {}
 
-    function latestPrice() public override(MedianOracle, Oracle) view returns (uint price, uint updateTime) {
-        (price, updateTime) = (savedPrice != 0) ? (savedPrice, savedUpdateTime) : super.latestPrice();
+    function latestPrice() public override(MedianOracle, Oracle) view returns (uint price) {
+        price = (savedPrice != 0) ? savedPrice : super.latestPrice();
     }
 }
diff --git a/contracts/mocks/MockUniswapV3Pool.sol b/contracts/mocks/MockUniswapV3Pool.sol
@@ -21,24 +21,6 @@ contract MockUniswapV3Pool {
         lastObservationIndex = observationIndex;
     }
 
-    function slot0() public view
-        returns (
-            uint160 sqrtPriceX96,
-            int24 tick,
-            uint16 observationIndex,
-            uint16 observationCardinality,
-            uint16 observationCardinalityNext,
-            uint8 feeProtocol,
-            bool unlocked
-        )
-    {
-        //Oracle.Observation memory lastObservation = observations[lastObservationIndex];
-        //tick = int24(lastObservation.tickCumulative);
-        tick = OracleLibrary.consult(address(this), 1);     // 1 because any positive period should do here
-        sqrtPriceX96 = TickMath.getSqrtRatioAtTick(tick);
-        return (sqrtPriceX96, tick, lastObservationIndex, 0, 0, 0, true);
-    }
-
     /**
      * @notice See also
      * https://github.com/Uniswap/uniswap-v3-core/blob/main/contracts/interfaces/pool/IUniswapV3PoolDerivedState.sol, where
diff --git a/contracts/mocks/SettableOracle.sol b/contracts/mocks/SettableOracle.sol
@@ -5,10 +5,8 @@ import "../oracles/Oracle.sol";
 
 abstract contract SettableOracle is Oracle {
     uint public savedPrice;
-    uint public savedUpdateTime;
 
     function setPrice(uint p) public {
         savedPrice = p;
-        savedUpdateTime = block.timestamp;
     }
 }
diff --git a/contracts/mocks/TestOracle.sol b/contracts/mocks/TestOracle.sol
@@ -8,7 +8,7 @@ contract TestOracle is SettableOracle {
         setPrice(p);
     }
 
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
-        return (savedPrice, savedUpdateTime);
+    function latestPrice() public virtual override view returns (uint price) {
+        return savedPrice;
     }
 }
diff --git a/contracts/oracles/ChainlinkOracle.sol b/contracts/oracles/ChainlinkOracle.sol
@@ -22,9 +22,8 @@ contract ChainlinkOracle is Oracle {
      * @notice Retrieve the latest price of the price oracle.
      * @return price
      */
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
-        int rawPrice;
-        (, rawPrice,, updateTime,) = chainlinkAggregator.latestRoundData();
+    function latestPrice() public virtual override view returns (uint price) {
+        (, int rawPrice,,,) = chainlinkAggregator.latestRoundData();
         require(rawPrice > 0, "Chainlink price <= 0");
         price = uint(rawPrice) * CHAINLINK_SCALE_FACTOR;
     }
diff --git a/contracts/oracles/MedianOracle.sol b/contracts/oracles/MedianOracle.sol
@@ -23,40 +23,32 @@ contract MedianOracle is ChainlinkOracle, UniswapV3TWAPOracle, UniswapV3TWAPOrac
         UniswapV3TWAPOracle2(uniswapPool2, uniswapTokenToPrice2, uniswapDecimals2) {}
 
     function latestPrice() public virtual override(ChainlinkOracle, UniswapV3TWAPOracle, UniswapV3TWAPOracle2)
-        view returns (uint price, uint updateTime)
+        view returns (uint price)
     {
-        (uint chainlinkPrice, uint chainlinkUpdateTime) = ChainlinkOracle.latestPrice();
-        (uint uniswapPrice1, uint uniswapUpdateTime1) = UniswapV3TWAPOracle.latestPrice();
-        (uint uniswapPrice2, uint uniswapUpdateTime2) = UniswapV3TWAPOracle2.latestPrice();
-        (price, updateTime) = medianPriceAndUpdateTime(chainlinkPrice, chainlinkUpdateTime,
-                                                       uniswapPrice1, uniswapUpdateTime1,
-                                                       uniswapPrice2, uniswapUpdateTime2);
+        price = median(ChainlinkOracle.latestPrice(),
+                       UniswapV3TWAPOracle.latestPrice(),
+                       UniswapV3TWAPOracle2.latestPrice());
     }
 
-    function latestChainlinkPrice() public view returns (uint price, uint updateTime) {
-        (price, updateTime) = ChainlinkOracle.latestPrice();
+    function latestChainlinkPrice() public view returns (uint price) {
+        price = ChainlinkOracle.latestPrice();
     }
 
-    function latestUniswapV3TWAPPrice1() public view returns (uint price, uint updateTime) {
-        (price, updateTime) = UniswapV3TWAPOracle.latestPrice();
+    function latestUniswapV3TWAPPrice1() public view returns (uint price) {
+        price = UniswapV3TWAPOracle.latestPrice();
     }
 
-    function latestUniswapV3TWAPPrice2() public view returns (uint price, uint updateTime) {
-        (price, updateTime) = UniswapV3TWAPOracle2.latestPrice();
+    function latestUniswapV3TWAPPrice2() public view returns (uint price) {
+        price = UniswapV3TWAPOracle2.latestPrice();
     }
 
     /**
      * @notice Currently only supports three inputs
-     * @return price the median price of the three passed in
-     * @return updateTime the updateTime corresponding to the median price.  Not the median of the three updateTimes!
+     * @return m the median of the three values passed in
      */
-    function medianPriceAndUpdateTime(uint p1, uint t1, uint p2, uint t2, uint p3, uint t3)
-        public pure returns (uint price, uint updateTime)
+    function median(uint a, uint b, uint c)
+        public pure returns (uint m)
     {
-        bool p1gtp2 = p1 > p2;
-        bool p2gtp3 = p2 > p3;
-        bool p3gtp1 = p3 > p1;
-
-        (price, updateTime) = (p3gtp1 == p1gtp2 ? (p1, t1) : (p1gtp2 == p2gtp3 ? (p2, t2) : (p3, t3)));
+        m = ((c > a) == (a > b) ? a : ((a > b) == (b > c) ? b : c));
     }
 }
diff --git a/contracts/oracles/Oracle.sol b/contracts/oracles/Oracle.sol
@@ -4,13 +4,6 @@ pragma solidity ^0.8.0;
 interface Oracle {
     /**
      * @return price WAD-scaled - 18 dec places
-     * @return updateTime The last time the price was updated.  This is a bit subtle: `price` can change without `updateTime`
-     * changing.  Suppose, eg, the current Uniswap v3 TWAP price over the last 10 minutes is $3,000, and then Uniswap records a
-     * new trade observation at a price of $2,980.  This will nudge the 10-minute TWAP slightly below $3,000, and reset
-     * `updateTime` to the new trade's time.  However, over the subsequent 10 minutes, the 10-minute TWAP will continue to
-     * decrease, as more and more of "the last 10 minutes" is at $2,980 rather than $3,000: but because this gradual price
-     * change is only driven by the passage of time, not by any new price observations, it will *not* change `updateTime`,
-     * which will remain at the time of the $2,980 trade until another trade occurs.
      */
-    function latestPrice() external view returns (uint price, uint updateTime);
+    function latestPrice() external view returns (uint price);
 }
diff --git a/contracts/oracles/UniswapV3TWAPOracle.sol b/contracts/oracles/UniswapV3TWAPOracle.sol
@@ -36,12 +36,10 @@ contract UniswapV3TWAPOracle is Oracle {
             WAD * 10 ** uint(-decimalPlaces));
     }
 
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
+    function latestPrice() public virtual override view returns (uint price) {
         int24 twapTick = OracleLibrary.consult(address(uniswapV3Pool), UNISWAP_TWAP_PERIOD);
         price = uniswapTokenToPrice == 1 ?
             OracleLibrary.getQuoteAtTick(twapTick, uniswapScaleFactor, uniswapV3Pool.token1(), uniswapV3Pool.token0()) :
             OracleLibrary.getQuoteAtTick(twapTick, uniswapScaleFactor, uniswapV3Pool.token0(), uniswapV3Pool.token1());
-        (,, uint16 observationIndex,,,,) = uniswapV3Pool.slot0();
-        (updateTime,,,) = uniswapV3Pool.observations(observationIndex);
     }
 }
diff --git a/contracts/oracles/UniswapV3TWAPOracle2.sol b/contracts/oracles/UniswapV3TWAPOracle2.sol
@@ -28,12 +28,10 @@ contract UniswapV3TWAPOracle2 is Oracle {
             WAD * 10 ** uint(-decimalPlaces));
     }
 
-    function latestPrice() public virtual override view returns (uint price, uint updateTime) {
+    function latestPrice() public virtual override view returns (uint price) {
         int24 twapTick = OracleLibrary.consult(address(uniswapV3Pool2), UNISWAP_TWAP_PERIOD_2);
         price = uniswapTokenToPrice2 == 1 ?
             OracleLibrary.getQuoteAtTick(twapTick, uniswapScaleFactor2, uniswapV3Pool2.token1(), uniswapV3Pool2.token0()) :
             OracleLibrary.getQuoteAtTick(twapTick, uniswapScaleFactor2, uniswapV3Pool2.token0(), uniswapV3Pool2.token1());
-        (,, uint16 observationIndex,,,,) = uniswapV3Pool2.slot0();
-        (updateTime,,,) = uniswapV3Pool2.observations(observationIndex);
     }
 }
diff --git a/test/01_TestOracle.test.js b/test/01_TestOracle.test.js
diff --git a/test/02_USM_internal.test.js b/test/02_USM_internal.test.js
diff --git a/test/03_USM.test.js b/test/03_USM.test.js

Original file line number	Diff line number	Diff line change
`@@ -14,9 +14,9 @@ contract GasMeasuredOracleWrapper is Oracle {`
`14`	`14`	`oracleName = name;`
`15`	`15`	`}`
`16`	`16`
`17`		`- function latestPrice() public virtual override view returns (uint price, uint updateTime) {`
	`17`	`+ function latestPrice() public virtual override view returns (uint price) {`
`18`	`18`	`uint gasStart = gasleft();`
`19`		`- (price, updateTime) = measuredOracle.latestPrice();`
	`19`	`+ price = measuredOracle.latestPrice();`
`20`	`20`	`uint gasEnd = gasleft();`
`21`	`21`	`console.log(" ", oracleName, "oracle.latestPrice() cost: ", gasStart - gasEnd);`
`22`	`22`	`}`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,7 @@ import "../oracles/ChainlinkOracle.sol";`
`12`	`12`	`contract MockChainlinkOracle is ChainlinkOracle, SettableOracle {`
`13`	`13`	`constructor(AggregatorV3Interface aggregator_) ChainlinkOracle(aggregator_) {}`
`14`	`14`
`15`		`- function latestPrice() public override(ChainlinkOracle, Oracle) view returns (uint price, uint updateTime) {`
`16`		`- (price, updateTime) = (savedPrice != 0) ? (savedPrice, savedUpdateTime) : super.latestPrice();`
	`15`	`+ function latestPrice() public override(ChainlinkOracle, Oracle) view returns (uint price) {`
	`16`	`+ price = (savedPrice != 0) ? savedPrice : super.latestPrice();`
`17`	`17`	`}`
`18`	`18`	`}`
Original file line number	Diff line number	Diff line change
`@@ -19,7 +19,7 @@ contract MockMedianOracle is MedianOracle, SettableOracle {`
`19`	`19`	`uniswapPool1, uniswapTokenToPrice1, uniswapDecimals1,`
`20`	`20`	`uniswapPool2, uniswapTokenToPrice2, uniswapDecimals2) {}`
`21`	`21`
`22`		`- function latestPrice() public override(MedianOracle, Oracle) view returns (uint price, uint updateTime) {`
`23`		`- (price, updateTime) = (savedPrice != 0) ? (savedPrice, savedUpdateTime) : super.latestPrice();`
	`22`	`+ function latestPrice() public override(MedianOracle, Oracle) view returns (uint price) {`
	`23`	`+ price = (savedPrice != 0) ? savedPrice : super.latestPrice();`
`24`	`24`	`}`
`25`	`25`	`}`
Original file line number	Diff line number	Diff line change
`@@ -5,10 +5,8 @@ import "../oracles/Oracle.sol";`
`5`	`5`
`6`	`6`	`abstract contract SettableOracle is Oracle {`
`7`	`7`	`uint public savedPrice;`
`8`		`- uint public savedUpdateTime;`
`9`	`8`
`10`	`9`	`function setPrice(uint p) public {`
`11`	`10`	`savedPrice = p;`
`12`		`- savedUpdateTime = block.timestamp;`
`13`	`11`	`}`
`14`	`12`	`}`
Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@ contract TestOracle is SettableOracle {`
`8`	`8`	`setPrice(p);`
`9`	`9`	`}`
`10`	`10`
`11`		`- function latestPrice() public virtual override view returns (uint price, uint updateTime) {`
`12`		`- return (savedPrice, savedUpdateTime);`
	`11`	`+ function latestPrice() public virtual override view returns (uint price) {`
	`12`	`+ return savedPrice;`
`13`	`13`	`}`
`14`	`14`	`}`