From 92b83a260bd7030e1709277a14f4b23d922422ab Mon Sep 17 00:00:00 2001
From: Derek May <32908855+riddlez666@users.noreply.github.com>
Date: Thu, 15 Mar 2018 09:08:35 -0700
Subject: [PATCH] Test of EXPDiff

---
 consensus/ethash/consensus.go | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index 422d8e0049..59712f45d9 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -298,11 +298,11 @@ func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Heade
 	next := new(big.Int).Add(parent.Number, big1)
 	switch {
 	case config.IsByzantium(next):
-		return calcDifficultyByzantium(time, parent)
+		return calcDifficultyEGEM(time, parent)
 	case config.IsHomestead(next):
-		return calcDifficultyHomestead(time, parent)
+		return calcDifficultyEGEM(time, parent)
 	default:
-		return calcDifficultyFrontier(time, parent)
+		return calcDifficultyEGEM(time, parent)
 	}
 }
 
@@ -458,6 +458,26 @@ func calcDifficultyFrontier(time uint64, parent *types.Header) *big.Int {
 	return diff
 }
 
+func calcDifficultyEGEM(time uint64, parent *types.Header) *big.Int {
+	diff := new(big.Int)
+	adjust := new(big.Int).Div(parent.Difficulty, big10)
+	bigTime := new(big.Int)
+	bigParentTime := new(big.Int)
+
+	bigTime.SetUint64(time)
+	bigParentTime.Set(parent.Time)
+
+	if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
+		diff.Add(parent.Difficulty, adjust)
+	} else {
+		diff.Sub(parent.Difficulty, adjust)
+	}
+	if diff.Cmp(params.MinimumDifficulty) < 0 {
+		diff.Set(params.MinimumDifficulty)
+	}
+	return diff
+}
+
 // VerifySeal implements consensus.Engine, checking whether the given block satisfies
 // the PoW difficulty requirements.
 func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Header) error {