make observe cheaper by not constructing a whole observation for which only 2 fields are used (#468)

Author: moodysalem

contracts/libraries/Oracle.sol

@@ -256,23 +256,25 @@ library Oracle {
         (Observation memory beforeOrAt, Observation memory atOrAfter) =
             getSurroundingObservations(self, time, target, tick, index, liquidity, cardinality);
 
-        Oracle.Observation memory at;
         if (target == beforeOrAt.blockTimestamp) {
             // we're at the left boundary
-            at = beforeOrAt;
+            return (beforeOrAt.tickCumulative, beforeOrAt.liquidityCumulative);
         } else if (target == atOrAfter.blockTimestamp) {
             // we're at the right boundary
-            at = atOrAfter;
+            return (atOrAfter.tickCumulative, atOrAfter.liquidityCumulative);
         } else {
             // we're in the middle
-            uint32 delta = atOrAfter.blockTimestamp - beforeOrAt.blockTimestamp;
-            int24 tickDerived = int24((atOrAfter.tickCumulative - beforeOrAt.tickCumulative) / delta);
-            uint128 liquidityDerived =
-                uint128((atOrAfter.liquidityCumulative - beforeOrAt.liquidityCumulative) / delta);
-            at = transform(beforeOrAt, target, tickDerived, liquidityDerived);
+            uint32 observationTimeDelta = atOrAfter.blockTimestamp - beforeOrAt.blockTimestamp;
+            uint32 targetDelta = target - beforeOrAt.blockTimestamp;
+            return (
+                beforeOrAt.tickCumulative +
+                    ((atOrAfter.tickCumulative - beforeOrAt.tickCumulative) / observationTimeDelta) *
+                    targetDelta,
+                beforeOrAt.liquidityCumulative +
+                    ((atOrAfter.liquidityCumulative - beforeOrAt.liquidityCumulative) / observationTimeDelta) *
+                    targetDelta
+            );
         }
-
-        return (at.tickCumulative, at.liquidityCumulative);
     }
 
     /// @notice Returns the accumulator values as of each time seconds ago from the given time in the array of `secondsAgos`

test/__snapshots__/Oracle.spec.ts.snap

@@ -10,7 +10,7 @@ exports[`Oracle #grow gas for growing by 10 slots when index == cardinality - 1
 
 exports[`Oracle #initialize gas 1`] = `70070`;
 
-exports[`Oracle #observe before initialization gas for observe since most recent 1`] = `4215`;
+exports[`Oracle #observe before initialization gas for observe since most recent 1`] = `4078`;
 
 exports[`Oracle #observe before initialization gas for single observation at current time 1`] = `2965`;
 
@@ -39,17 +39,17 @@ Object {
 }
 `;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas all of last 20 seconds 1`] = `146696`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas all of last 20 seconds 1`] = `139585`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas between oldest and oldest + 1 1`] = `11239`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas between oldest and oldest + 1 1`] = `10711`;
 
 exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas latest equal 1`] = `2965`;
 
 exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas latest transform 1`] = `3399`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas middle 1`] = `11414`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas middle 1`] = `10886`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas oldest 1`] = `10575`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 5 gas oldest 1`] = `10438`;
 
 exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 fetch many values 1`] = `
 Object {
@@ -74,14 +74,14 @@ Object {
 }
 `;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas all of last 20 seconds 1`] = `146696`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas all of last 20 seconds 1`] = `139585`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas between oldest and oldest + 1 1`] = `11239`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas between oldest and oldest + 1 1`] = `10711`;
 
 exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas latest equal 1`] = `2965`;
 
 exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas latest transform 1`] = `3399`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas middle 1`] = `11414`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas middle 1`] = `10886`;
 
-exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas oldest 1`] = `10575`;
+exports[`Oracle #observe initialized with 5 observations with starting time of 4294967291 gas oldest 1`] = `10438`;

test/__snapshots__/UniswapV3Factory.spec.ts.snap

@@ -1,7 +1,7 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`UniswapV3Factory #createPool gas 1`] = `4510482`;
+exports[`UniswapV3Factory #createPool gas 1`] = `4512482`;
 
-exports[`UniswapV3Factory factory bytecode size 1`] = `24320`;
+exports[`UniswapV3Factory factory bytecode size 1`] = `24330`;
 
-exports[`UniswapV3Factory pool bytecode size 1`] = `21897`;
+exports[`UniswapV3Factory pool bytecode size 1`] = `21907`;