feat: L1Block uses average L1 basefee

packages/contracts-bedrock/.gas-snapshot

@@ -3,7 +3,7 @@ DeployerWhitelist_Test:test_owner() (gas: 7647)
 DeployerWhitelist_Test:test_storageSlots() (gas: 33483)
 GasPriceOracle_Test:test_baseFee() (gas: 8395)
 GasPriceOracle_Test:test_gasPrice() (gas: 8384)
-GasPriceOracle_Test:test_l1BaseFee() (gas: 10626)
+GasPriceOracle_Test:test_l1BaseFee() (gas: 11373)
 GasPriceOracle_Test:test_onlyOwnerSetDecimals() (gas: 10575)
 GasPriceOracle_Test:test_onlyOwnerSetOverhead() (gas: 10599)
 GasPriceOracle_Test:test_onlyOwnerSetScalar() (gas: 10640)
@@ -14,12 +14,13 @@ GasPriceOracle_Test:test_setL1BaseFeeReverts() (gas: 11658)
 GasPriceOracle_Test:test_setOverhead() (gas: 36767)
 GasPriceOracle_Test:test_setScalar() (gas: 36840)
 GasPriceOracle_Test:test_storageLayout() (gas: 86683)
-L1BlockTest:test_basefee() (gas: 7575)
+L1BlockTest:test_averageBasefee() (gas: 7946)
+L1BlockTest:test_basefee() (gas: 7553)
 L1BlockTest:test_hash() (gas: 7552)
 L1BlockTest:test_number() (gas: 7651)
-L1BlockTest:test_sequenceNumber() (gas: 7596)
+L1BlockTest:test_sequenceNumber() (gas: 7661)
 L1BlockTest:test_timestamp() (gas: 7683)
-L1BlockTest:test_updateValues() (gas: 23144)
+L1BlockTest:test_updateValues() (gas: 46016)
 L1BlockNumberTest:test_fallback() (gas: 10755)
 L1BlockNumberTest:test_getL1BlockNumber() (gas: 10589)
 L1BlockNumberTest:test_receive() (gas: 17418)

packages/contracts-bedrock/contracts/L2/GasPriceOracle.sol

@@ -68,7 +68,7 @@ contract GasPriceOracle is Ownable {
     }
 
     function l1BaseFee() public view returns (uint256) {
-        return L1Block(Lib_PredeployAddresses.L1_BLOCK_ATTRIBUTES).basefee();
+        return L1Block(Lib_PredeployAddresses.L1_BLOCK_ATTRIBUTES).averageBasefee();
     }
 
     /**

packages/contracts-bedrock/contracts/L2/L1Block.sol

@@ -1,6 +1,8 @@
 //SPDX-License-Identifier: MIT
 pragma solidity 0.8.10;
 
+import { Lib_FeeSmoothing } from "../libraries/Lib_FeeSmoothing.sol";
+
 /**
  * @title L1Block
  * @dev This is an L2 predeploy contract that holds values from the L1
@@ -40,6 +42,11 @@ contract L1Block {
      */
     uint256 public basefee;
 
+    /**
+     * @notice The average L1 basefee
+     */
+    uint256 public averageBasefee;
+
     /**
      * @notice The latest L1 blockhash
      */
@@ -75,5 +82,15 @@ contract L1Block {
             sstore(basefee.slot, _basefee)
             sstore(hash.slot, _hash)
         }
+
+        averageBasefee = _nextAverageBasefee(_basefee);
+    }
+
+    /**
+     * @notice Compute the running average L1 basefee
+     */
+
+    function _nextAverageBasefee(uint256 _basefee) internal returns (uint256) {
+        return Lib_FeeSmoothing.rollingAverage(averageBasefee, _basefee);
     }
 }

packages/contracts-bedrock/contracts/libraries/Lib_FeeSmoothing.sol

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.9;
+
+import { FixedPointMathLib } from "@rari-capital/solmate/src/utils/FixedPointMathLib.sol";
+
+/**
+ * @title Lib_FeeSmoothing
+ */
+library Lib_FeeSmoothing {
+    /**
+     * @notice Weight applied to average
+     */
+    uint256 constant internal prevWeight = 7e18;
+
+    /**
+     * @notice Weight applied to value being added to average
+     */
+    uint256 constant internal nextWeight = 3e18;
+
+    /**
+     * @notice Computes a rolling average
+     */
+    function rollingAverage(
+        uint256 prev,
+        uint256 next
+    ) internal returns (uint256) {
+        uint256 a = saturatingMul(prev, FixedPointMathLib.divWadDown(prevWeight, 1e19));
+        uint256 b = saturatingMul(next, FixedPointMathLib.divWadDown(nextWeight, 1e19));
+        return saturatingAdd(a, b) / 1e18;
+    }
+
+    /**
+     * @notice Saturating multiplication
+     */
+    function saturatingMul(uint256 a, uint256 b) internal returns (uint256) {
+        unchecked {
+            if (a == 0) {
+                return 0;
+            }
+            uint256 c = a * b;
+            if (c / a != b) {
+                return type(uint256).max;
+            }
+            return c;
+        }
+    }
+
+    /**
+     * @notice Saturating addition
+     */
+    function saturatingAdd(uint256 a, uint256 b) internal returns (uint256) {
+        unchecked {
+            uint256 c = a + b;
+            if (c < a) {
+                return type(uint256).max;
+            }
+            return c;
+        }
+    }
+}

packages/contracts-bedrock/contracts/test/GasPriceOracle.t.sol

@@ -5,6 +5,7 @@ import { CommonTest } from "./CommonTest.t.sol";
 import { GasPriceOracle } from "../L2/GasPriceOracle.sol";
 import { L1Block } from "../L2/L1Block.sol";
 import { Lib_PredeployAddresses } from "../libraries/Lib_PredeployAddresses.sol";
+import { Lib_FeeSmoothing } from "../libraries/Lib_FeeSmoothing.sol";
 
 contract GasPriceOracle_Test is CommonTest {
 
@@ -81,7 +82,8 @@ contract GasPriceOracle_Test is CommonTest {
 
     function test_l1BaseFee() external {
         uint256 l1BaseFee = gasOracle.l1BaseFee();
-        assertEq(l1BaseFee, 100);
+        uint256 expect = Lib_FeeSmoothing.rollingAverage(0, 100);
+        assertEq(l1BaseFee, expect);
     }
 
     function test_gasPrice() external {

packages/contracts-bedrock/contracts/test/L1Block.t.sol

@@ -3,12 +3,15 @@ pragma solidity 0.8.10;
 
 import { CommonTest } from "./CommonTest.t.sol";
 import { L1Block } from "../L2/L1Block.sol";
+import { Lib_FeeSmoothing } from "../libraries/Lib_FeeSmoothing.sol";
 
 contract L1BlockTest is CommonTest {
     L1Block lb;
     address depositor;
     bytes32 immutable NON_ZERO_HASH = keccak256(abi.encode(1));
 
+    uint256 averageBasefee;
+
     function setUp() external {
         lb = new L1Block();
         depositor = lb.DEPOSITOR_ACCOUNT();
@@ -17,11 +20,14 @@ contract L1BlockTest is CommonTest {
     }
 
     function test_updatesValues(uint64 n, uint64 t, uint256 b, bytes32 h, uint64 s) external {
+        averageBasefee = Lib_FeeSmoothing.rollingAverage(averageBasefee, b);
+
         vm.prank(depositor);
         lb.setL1BlockValues(n, t, b, h, s);
         assertEq(lb.number(), n);
         assertEq(lb.timestamp(), t);
         assertEq(lb.basefee(), b);
+        assertEq(lb.averageBasefee(), averageBasefee);
         assertEq(lb.hash(), h);
         assertEq(lb.sequenceNumber(), s);
     }
@@ -38,6 +44,11 @@ contract L1BlockTest is CommonTest {
         assertEq(lb.basefee(), 3);
     }
 
+    function test_averageBasefee() external {
+        uint256 expect = Lib_FeeSmoothing.rollingAverage(0, 3);
+        assertEq(lb.averageBasefee(), expect);
+    }
+
     function test_hash() external {
         assertEq(lb.hash(), NON_ZERO_HASH);
     }

packages/contracts-bedrock/contracts/test/Lib_RLP.t.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: Unlicense
 pragma solidity >=0.8.0;
 
-import {Bytes32AddressLib} from "solmate/utils/Bytes32AddressLib.sol";
+import {Bytes32AddressLib} from "@rari-capital/solmate/src/utils/Bytes32AddressLib.sol";
 
 // prettier-ignore
 library LibRLP {

packages/contracts-bedrock/foundry.toml

@@ -7,8 +7,7 @@ optimizer_runs = 999999
 remappings = [
   '@openzeppelin/contracts-upgradeable/=node_modules/@openzeppelin/contracts-upgradeable/',
   '@openzeppelin/contracts/=node_modules/@openzeppelin/contracts/',
-  'excessively-safe-call/=node_modules/excessively-safe-call/src/',
-  'solmate/=node_modules/@rari-capital/solmate/src',
+  '@rari-capital/solmate/=node_modules/@rari-capital/solmate',
   'forge-std/=node_modules/forge-std/src',
   'ds-test/=node_modules/ds-test/src'
 ]