Pack heap size + array length

src/HeapOrdering.sol

@@ -10,8 +10,9 @@ library HeapOrdering {
     }
 
     struct HeapArray {
-        Account[] accounts; // All the accounts.
-        uint256 size; // The size of the heap portion of the structure, should be less than accounts length, the rest is an unordered array.
+        mapping(uint256 => Account) accounts; // All the accounts.
+        uint128 arrayLength; // The length of the array represented by the `accounts` mapping.
+        uint128 size; // The size of the heap portion of the structure, should be less than `arrayLength`, the rest is an unordered array.
         mapping(address => uint256) indexOf; // A mapping from an address to an index in accounts. From index i, the parent index is (i-1)/2, the left child index is 2*i+1 and the right child index is 2*i+2.
     }
 
@@ -45,7 +46,7 @@ library HeapOrdering {
 
         uint256 size = _heap.size;
         uint256 newSize = computeSize(size, _maxSortedUsers);
-        if (size != newSize) _heap.size = newSize;
+        if (size != newSize) _heap.size = uint128(newSize);
 
         if (formerValue != newValue) {
             if (newValue == 0) remove(_heap, newSize, _id, formerValue);
@@ -181,14 +182,15 @@ library HeapOrdering {
         if (_id == address(0)) revert AddressIsZero();
 
         // Put the account at the end of accounts.
-        uint256 accountsLength = _heap.accounts.length;
-        _heap.accounts.push(Account(_id, _value));
+        uint256 accountsLength = _heap.arrayLength;
+        _heap.accounts[accountsLength] = Account(_id, _value);
+        _heap.arrayLength = uint128(accountsLength + 1);
         _heap.indexOf[_id] = accountsLength;
 
         // Move the account at the end of the heap and restore the invariant.
         swap(_heap, _size, accountsLength);
         shiftUp(_heap, _size);
-        _heap.size = computeSize(_size + 1, _maxSortedUsers);
+        _heap.size = uint128(computeSize(_size + 1, _maxSortedUsers));
     }
 
     /// @notice Decreases the amount of an account in the `_heap`.
@@ -231,7 +233,7 @@ library HeapOrdering {
         else {
             swap(_heap, _size, index);
             shiftUp(_heap, _size);
-            _heap.size = computeSize(_size + 1, _maxSortedUsers);
+            _heap.size = uint128(computeSize(_size + 1, _maxSortedUsers));
         }
     }
 
@@ -248,12 +250,14 @@ library HeapOrdering {
         uint96 _removedValue
     ) private {
         uint256 index = _heap.indexOf[_id];
-        uint256 accountsLength = _heap.accounts.length;
-
-        // Swap the last account and the account to remove, then pop it.
-        swap(_heap, index, accountsLength - 1);
-        if (_size == accountsLength) _heap.size = --_size;
-        _heap.accounts.pop();
+        uint256 accountsLength = _heap.arrayLength;
+
+        // Swap the last account and the account to remove, then "pop" it.
+        uint256 newArrayLength = accountsLength - 1;
+        swap(_heap, index, newArrayLength);
+        if (_size == accountsLength) _heap.size = uint128(--_size);
+        delete _heap.accounts[newArrayLength];
+        _heap.arrayLength = uint128(newArrayLength);
         delete _heap.indexOf[_id];
 
         // If the swapped account is in the heap, restore the invariant: its value can be smaller or larger than the removed value.
@@ -269,7 +273,7 @@ library HeapOrdering {
     /// @param _heap The heap parameter.
     /// @return The length of the heap.
     function length(HeapArray storage _heap) internal view returns (uint256) {
-        return _heap.accounts.length;
+        return _heap.arrayLength;
     }
 
     /// @notice Returns the value of the account linked to `_id`.
@@ -278,27 +282,27 @@ library HeapOrdering {
     /// @return The value of the account.
     function getValueOf(HeapArray storage _heap, address _id) internal view returns (uint256) {
         uint256 index = _heap.indexOf[_id];
-        if (index >= _heap.accounts.length) return 0;
+        if (index >= _heap.arrayLength) return 0;
         Account memory account = _heap.accounts[index];
         if (account.id != _id) return 0;
-        else return account.value;
+        return account.value;
     }
 
     /// @notice Returns the address at the head of the `_heap`.
     /// @param _heap The heap to get the head.
     /// @return The address of the head.
     function getHead(HeapArray storage _heap) internal view returns (address) {
-        if (_heap.accounts.length > 0) return _heap.accounts[ROOT].id;
-        else return address(0);
+        if (_heap.arrayLength > 0) return _heap.accounts[ROOT].id;
+        return address(0);
     }
 
     /// @notice Returns the address at the tail of unsorted portion of the `_heap`.
     /// @param _heap The heap to get the tail.
     /// @return The address of the tail.
     function getTail(HeapArray storage _heap) internal view returns (address) {
-        uint256 accountsLength = _heap.accounts.length;
+        uint256 accountsLength = _heap.arrayLength;
         if (accountsLength > 0) return _heap.accounts[accountsLength - 1].id;
-        else return address(0);
+        return address(0);
     }
 
     /// @notice Returns the address coming before `_id` in accounts.
@@ -309,7 +313,7 @@ library HeapOrdering {
     function getPrev(HeapArray storage _heap, address _id) internal view returns (address) {
         uint256 index = _heap.indexOf[_id];
         if (index > ROOT) return _heap.accounts[index - 1].id;
-        else return address(0);
+        return address(0);
     }
 
     /// @notice Returns the address coming after `_id` in accounts.
@@ -319,8 +323,7 @@ library HeapOrdering {
     /// @return The address of the next account.
     function getNext(HeapArray storage _heap, address _id) internal view returns (address) {
         uint256 index = _heap.indexOf[_id];
-        if (index + 1 >= _heap.accounts.length || _heap.accounts[index].id != _id)
-            return address(0);
-        else return _heap.accounts[index + 1].id;
+        if (index + 1 >= _heap.arrayLength || _heap.accounts[index].id != _id) return address(0);
+        return _heap.accounts[index + 1].id;
     }
 }