1 files changed, 23 insertions, 15 deletions
diff --git a/core/evm.go b/core/evm.go
index 796b312..74891d7 100644
--- a/core/evm.go
+++ b/core/evm.go
@@ -22,8 +22,8 @@ import (
 	"github.com/ava-labs/coreth/consensus"
 	"github.com/ava-labs/coreth/core/types"
 	"github.com/ava-labs/coreth/core/vm"
-	"github.com/ava-labs/go-ethereum/common"
-	"github.com/ava-labs/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/log"
 )
 
 // ChainContext supports retrieving headers and consensus parameters from the
@@ -63,24 +63,32 @@ func NewEVMContext(msg Message, header *types.Header, chain ChainContext, author
 
 // GetHashFn returns a GetHashFunc which retrieves header hashes by number
 func GetHashFn(ref *types.Header, chain ChainContext) func(n uint64) common.Hash {
-	var cache map[uint64]common.Hash
+	// Cache will initially contain [refHash.parent],
+	// Then fill up with [refHash.p, refHash.pp, refHash.ppp, ...]
+	var cache []common.Hash
 
 	return func(n uint64) common.Hash {
 		// If there's no hash cache yet, make one
-		if cache == nil {
-			cache = map[uint64]common.Hash{
-				ref.Number.Uint64() - 1: ref.ParentHash,
-			}
+		if len(cache) == 0 {
+			cache = append(cache, ref.ParentHash)
 		}
-		// Try to fulfill the request from the cache
-		if hash, ok := cache[n]; ok {
-			return hash
+		if idx := ref.Number.Uint64() - n - 1; idx < uint64(len(cache)) {
+			return cache[idx]
 		}
-		// Not cached, iterate the blocks and cache the hashes
-		for header := chain.GetHeader(ref.ParentHash, ref.Number.Uint64()-1); header != nil; header = chain.GetHeader(header.ParentHash, header.Number.Uint64()-1) {
-			cache[header.Number.Uint64()-1] = header.ParentHash
-			if n == header.Number.Uint64()-1 {
-				return header.ParentHash
+		// No luck in the cache, but we can start iterating from the last element we already know
+		lastKnownHash := cache[len(cache)-1]
+		lastKnownNumber := ref.Number.Uint64() - uint64(len(cache))
+
+		for {
+			header := chain.GetHeader(lastKnownHash, lastKnownNumber)
+			if header == nil {
+				break
+			}
+			cache = append(cache, header.ParentHash)
+			lastKnownHash = header.ParentHash
+			lastKnownNumber = header.Number.Uint64() - 1
+			if n == lastKnownNumber {
+				return lastKnownHash
 			}
 		}
 		return common.Hash{}