Use ring buffer for chain contracts

packages/contracts/contracts/optimistic-ethereum/OVM/chain/OVM_BaseChain.sol

@@ -8,6 +8,7 @@ import { iOVM_BaseChain } from "../../iOVM/chain/iOVM_BaseChain.sol";
 /* Library Imports */
 import { Lib_OVMCodec } from "../../libraries/codec/Lib_OVMCodec.sol";
 import { Lib_MerkleUtils } from "../../libraries/utils/Lib_MerkleUtils.sol";
+import { TimeboundRingBuffer, Lib_TimeboundRingBuffer } from "../../libraries/utils/Lib_TimeboundRingBuffer.sol";
 
 /**
  * @title OVM_BaseChain
@@ -18,11 +19,23 @@ contract OVM_BaseChain is iOVM_BaseChain {
      * Contract Variables: Batches *
      *******************************/
 
-    bytes32[] internal batches;
+    using Lib_TimeboundRingBuffer for TimeboundRingBuffer;
+    TimeboundRingBuffer internal batches;
     uint256 internal totalBatches;
     uint256 internal totalElements;
 
 
+    /***************
+     * Constructor *
+     ***************/
+
+    constructor()
+    {
+        // TODO: Add propper customization
+        batches.init(4, 2, 100000);
+    }
+
+
     /*************************************
      * Public Functions: Batch Retrieval *
      *************************************/
@@ -39,7 +52,7 @@ contract OVM_BaseChain is iOVM_BaseChain {
             uint256 _totalElements
         )
     {
-        return totalElements;
+        return uint256(uint224(batches.getExtraData()));
     }
 
     /**
@@ -54,7 +67,7 @@ contract OVM_BaseChain is iOVM_BaseChain {
             uint256 _totalBatches
         )
     {
-        return totalBatches;
+        return uint256(batches.getLength());
     }
 
 
@@ -82,7 +95,7 @@ contract OVM_BaseChain is iOVM_BaseChain {
         )
     {
         require(
-            _hashBatchHeader(_batchHeader) == batches[_batchHeader.batchIndex],
+            _hashBatchHeader(_batchHeader) == batches.get(uint32(_batchHeader.batchIndex)),
             "Invalid batch header."
         );
 
@@ -114,9 +127,7 @@ contract OVM_BaseChain is iOVM_BaseChain {
         internal
     {
         bytes32 batchHeaderHash = _hashBatchHeader(_batchHeader);
-        batches.push(batchHeaderHash);
-        totalBatches += 1;
-        totalElements += _batchHeader.batchSize;
+        batches.push(batchHeaderHash, bytes28(uint224(getTotalElements() + _batchHeader.batchSize)));
     }
 
     /**
@@ -131,7 +142,7 @@ contract OVM_BaseChain is iOVM_BaseChain {
         internal
     {
         Lib_OVMCodec.ChainBatchHeader memory batchHeader = Lib_OVMCodec.ChainBatchHeader({
-            batchIndex: batches.length,
+            batchIndex: uint(batches.getLength()),
             batchRoot: Lib_MerkleUtils.getMerkleRoot(_elements),
             batchSize: _elements.length,
             prevTotalElements: totalElements,
@@ -166,17 +177,17 @@ contract OVM_BaseChain is iOVM_BaseChain {
         internal
     {
         require(
-            _batchHeader.batchIndex < batches.length,
+            _batchHeader.batchIndex < batches.getLength(),
             "Invalid batch index."
         );
 
         require(
-            _hashBatchHeader(_batchHeader) == batches[_batchHeader.batchIndex],
+            _hashBatchHeader(_batchHeader) == batches.get(uint32(_batchHeader.batchIndex)),
             "Invalid batch header."
         );
 
-        totalBatches = _batchHeader.batchIndex;
         totalElements = _batchHeader.prevTotalElements;
+        batches.deleteElementsAfter(uint32(_batchHeader.batchIndex - 1), bytes28(uint224(totalElements)));
     }
 
 

packages/contracts/contracts/test-libraries/utils/TestLib_TimeboundRingBuffer.sol

@@ -2,9 +2,6 @@
 pragma solidity ^0.7.0;
 pragma experimental ABIEncoderV2;
 
-/* Logging */
-import { console } from "@nomiclabs/buidler/console.sol";
-
 /* Library Imports */
 import { TimeboundRingBuffer, Lib_TimeboundRingBuffer } from "../../optimistic-ethereum/libraries/utils/Lib_TimeboundRingBuffer.sol";