Remove difficulty bomb for Atlantis difficulty calculation (#69)

* Removed difficulty bomb for atlantis difficulty calculation

* Skipped tests that include difficulty change from non-existant difficulty bomb ETH -> ETC

core/block_validator.go

@@ -314,7 +314,6 @@ func CalcDifficulty(config *ChainConfig, time uint64, parent *types.Header) *big
 
 // Some weird constants to avoid constant memory allocs for them.
 var (
-	expDiffPeriod = big.NewInt(100000)
 	big1          = big.NewInt(1)
 	big2          = big.NewInt(2)
 	big9          = big.NewInt(9)
@@ -323,7 +322,6 @@ var (
 )
 
 func calcDifficultyAtlantis(time uint64, parent *types.Header) *big.Int {
-	bombDelayFromParent := new(big.Int).Sub(big.NewInt(3000000), big1)
 	// https://github.com/ethereum/EIPs/issues/100.
 	// algorithm:
 	// diff = (parent_diff +
@@ -358,23 +356,6 @@ func calcDifficultyAtlantis(time uint64, parent *types.Header) *big.Int {
 	if x.Cmp(params.MinimumDifficulty) < 0 {
 		x.Set(params.MinimumDifficulty)
 	}
-	// calculate a fake block number for the ice-age delay
-	// Specification: https://eips.ethereum.org/EIPS/eip-1234
-	fakeBlockNumber := new(big.Int)
-	if parent.Number.Cmp(bombDelayFromParent) >= 0 {
-		fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, bombDelayFromParent)
-	}
-	// for the exponential factor
-	periodCount := fakeBlockNumber
-	periodCount.Div(periodCount, expDiffPeriod)
-
-	// the exponential factor, commonly referred to as "the bomb"
-	// diff = diff + 2^(periodCount - 2)
-	if periodCount.Cmp(big1) > 0 {
-		y.Sub(periodCount, big2)
-		y.Exp(big2, y, nil)
-		x.Add(x, y)
-	}
 	return x
 }
 

tests/difficulty_test_util.go

@@ -52,6 +52,10 @@ func (test *DifficultyTest) runDifficulty(t *testing.T, config *core.ChainConfig
 		UncleHash:  test.UncleHash,
 	}
 
+	if config.IsAtlantis(parentNumber) && parent.Number.Cmp(big.NewInt(3199999)) >= 0 {
+		return nil
+	}
+
 	// Check to make sure difficulty is above minimum
 	if parentDifficulty.Cmp(params.MinimumDifficulty) < 0 {
 		t.Skip("difficulty below minimum")