[ETCM-942] Implement Muir Glacier delay

Author: lukasz-golebiewski

src/main/scala/io/iohk/ethereum/consensus/pow/difficulty/EthashDifficultyCalculator.scala

@@ -9,6 +9,7 @@ object EthashDifficultyCalculator extends DifficultyCalculator {
   private val ExpDifficultyPeriod: Int = 100000
   private val ByzantiumRelaxDifficulty: BigInt = 3000000
   private val ConstantinopleRelaxDifficulty: BigInt = 5000000
+  private val MuirGlacierRelaxDifficulty: BigInt = 9000000
 
   def calculateDifficulty(blockNumber: BigInt, blockTimestamp: Long, parentHeader: BlockHeader)(implicit
       blockchainConfig: BlockchainConfig
@@ -32,8 +33,10 @@ object EthashDifficultyCalculator extends DifficultyCalculator {
       if (blockNumber < difficultyBombRemovalBlockNumber) {
         // calculate a fake block number for the ice-age delay
         val fakeBlockNumber: BigInt =
+          // https://eips.ethereum.org/EIPS/eip-2384
+          if (blockNumber >= muirGlacierBlockNumber) (blockNumber - MuirGlacierRelaxDifficulty).max(0)
           // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1234.md
-          if (blockNumber >= constantinopleBlockNumber) (blockNumber - ConstantinopleRelaxDifficulty).max(0)
+          else if (blockNumber >= constantinopleBlockNumber) (blockNumber - ConstantinopleRelaxDifficulty).max(0)
           // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-649.md
           else if (blockNumber >= byzantiumBlockNumber) (blockNumber - ByzantiumRelaxDifficulty).max(0)
           else blockNumber

src/test/scala/io/iohk/ethereum/consensus/pow/validators/EthashBlockHeaderValidatorSpec.scala

@@ -254,6 +254,36 @@ class EthashBlockHeaderValidatorSpec
     difficulty shouldBe afterRewardReductionBlockHeader.difficulty
   }
 
+  it should "properly calculate the difficulty after muir glacier delay" in new EphemBlockchainTestSetup {
+    val blockchainConfigWithoutDifficultyBombRemoval: BlockchainConfig =
+      blockchainConfig.withUpdatedForkBlocks(
+        _.copy(
+          difficultyBombRemovalBlockNumber = BigInt("1000000000000"),
+          difficultyBombPauseBlockNumber = 0,
+          difficultyBombContinueBlockNumber = 0,
+          muirGlacierBlockNumber = 9200000
+        )
+      )
+
+    val parentHeader: BlockHeader =
+      validParentBlockHeader.copy(
+        number = 9200000 - 1,
+        unixTimestamp = 1525176000,
+        difficulty = BigInt("22627021745803")
+      )
+    val parent = Block(parentHeader, parentBody)
+
+    val blockNumber: BigInt = parentHeader.number + 1
+    val blockTimestamp: Long = parentHeader.unixTimestamp + 6
+
+    val difficulty: BigInt = EthashDifficultyCalculator.calculateDifficulty(blockNumber, blockTimestamp, parent.header)(
+      blockchainConfigWithoutDifficultyBombRemoval
+    )
+    val blockDifficultyWihtoutBomb = BigInt("22638070096265")
+
+    difficulty shouldBe blockDifficultyWihtoutBomb
+  }
+
   // FIXME: Replace with mocked miner validators once we have them
   object BlockValidatorWithPowMocked extends BlockHeaderValidatorSkeleton() {
 
@@ -388,6 +418,7 @@ class EthashBlockHeaderValidatorSpec
         byzantiumBlockNumber = 4370000,
         constantinopleBlockNumber = 7280000,
         istanbulBlockNumber = 9069000,
+        muirGlacierBlockNumber = 9200000,
         eip106BlockNumber = 0
       ),
       daoForkConfig = Some(new DaoForkConfig {