Extend Checkpoints with new sizes and lookup mechanisms (#3589)

contracts/utils/Arrays.sol

@@ -3,12 +3,15 @@
 
 pragma solidity ^0.8.0;
 
+import "./StorageSlot.sol";
 import "./math/Math.sol";
 
 /**
  * @dev Collection of functions related to array types.
  */
 library Arrays {
+    using StorageSlot for bytes32;
+
     /**
      * @dev Searches a sorted `array` and returns the first index that contains
      * a value greater or equal to `element`. If no such index exists (i.e. all
@@ -31,7 +34,7 @@ library Arrays {
 
             // Note that mid will always be strictly less than high (i.e. it will be a valid array index)
             // because Math.average rounds down (it does integer division with truncation).
-            if (array[mid] > element) {
+            if (unsafeAccess(array, mid).value > element) {
                 high = mid;
             } else {
                 low = mid + 1;
@@ -39,10 +42,55 @@ library Arrays {
         }
 
         // At this point `low` is the exclusive upper bound. We will return the inclusive upper bound.
-        if (low > 0 && array[low - 1] == element) {
+        if (low > 0 && unsafeAccess(array, low - 1).value == element) {
             return low - 1;
         } else {
             return low;
         }
     }
+
+    /**
+     * @dev Access an array in an "unsafe" way. Skips solidity "index-out-of-range" check.
+     *
+     * WARNING: Only use if you are certain `pos` is lower than the array length.
+     */
+    function unsafeAccess(address[] storage arr, uint256 pos) internal pure returns (StorageSlot.AddressSlot storage) {
+        bytes32 slot;
+        /// @solidity memory-safe-assembly
+        assembly {
+            mstore(0, arr.slot)
+            slot := add(keccak256(0, 0x20), pos)
+        }
+        return slot.getAddressSlot();
+    }
+
+    /**
+     * @dev Access an array in an "unsafe" way. Skips solidity "index-out-of-range" check.
+     *
+     * WARNING: Only use if you are certain `pos` is lower than the array length.
+     */
+    function unsafeAccess(bytes32[] storage arr, uint256 pos) internal pure returns (StorageSlot.Bytes32Slot storage) {
+        bytes32 slot;
+        /// @solidity memory-safe-assembly
+        assembly {
+            mstore(0, arr.slot)
+            slot := add(keccak256(0, 0x20), pos)
+        }
+        return slot.getBytes32Slot();
+    }
+
+    /**
+     * @dev Access an array in an "unsafe" way. Skips solidity "index-out-of-range" check.
+     *
+     * WARNING: Only use if you are certain `pos` is lower than the array length.
+     */
+    function unsafeAccess(uint256[] storage arr, uint256 pos) internal pure returns (StorageSlot.Uint256Slot storage) {
+        bytes32 slot;
+        /// @solidity memory-safe-assembly
+        assembly {
+            mstore(0, arr.slot)
+            slot := add(keccak256(0, 0x20), pos)
+        }
+        return slot.getUint256Slot();
+    }
 }