consensus/ethash: add maxEpoch constant

consensus/ethash/algorithm.go

@@ -355,9 +355,11 @@ func hashimotoFull(dataset []uint32, hash []byte, nonce uint64) ([]byte, []byte)
 	return hashimoto(hash, nonce, uint64(len(dataset))*4, lookup)
 }
 
+const maxEpoch = 2048
+
 // datasetSizes is a lookup table for the ethash dataset size for the first 2048
 // epochs (i.e. 61440000 blocks).
-var datasetSizes = []uint64{
+var datasetSizes = [maxEpoch]uint64{
 	1073739904, 1082130304, 1090514816, 1098906752, 1107293056,
 	1115684224, 1124070016, 1132461952, 1140849536, 1149232768,
 	1157627776, 1166013824, 1174404736, 1182786944, 1191180416,
@@ -771,7 +773,7 @@ var datasetSizes = []uint64{
 
 // cacheSizes is a lookup table for the ethash verification cache size for the
 // first 2048 epochs (i.e. 61440000 blocks).
-var cacheSizes = []uint64{
+var cacheSizes = [maxEpoch]uint64{
 	16776896, 16907456, 17039296, 17170112, 17301056, 17432512, 17563072,
 	17693888, 17824192, 17955904, 18087488, 18218176, 18349504, 18481088,
 	18611392, 18742336, 18874304, 19004224, 19135936, 19267264, 19398208,

consensus/ethash/algorithm_go1.7.go

@@ -25,7 +25,7 @@ package ethash
 func cacheSize(block uint64) uint64 {
 	// If we have a pre-generated value, use that
 	epoch := int(block / epochLength)
-	if epoch < len(cacheSizes) {
+	if epoch < maxEpoch {
 		return cacheSizes[epoch]
 	}
 	// We don't have a way to verify primes fast before Go 1.8
@@ -39,7 +39,7 @@ func cacheSize(block uint64) uint64 {
 func datasetSize(block uint64) uint64 {
 	// If we have a pre-generated value, use that
 	epoch := int(block / epochLength)
-	if epoch < len(datasetSizes) {
+	if epoch < maxEpoch {
 		return datasetSizes[epoch]
 	}
 	// We don't have a way to verify primes fast before Go 1.8

consensus/ethash/algorithm_go1.8.go

@@ -27,10 +27,14 @@ import "math/big"
 func cacheSize(block uint64) uint64 {
 	// If we have a pre-generated value, use that
 	epoch := int(block / epochLength)
-	if epoch < len(cacheSizes) {
+	if epoch < maxEpoch {
 		return cacheSizes[epoch]
 	}
 	// No known cache size, calculate manually (sanity branch only)
+	return calcCacheSize(epoch)
+}
+
+func calcCacheSize(epoch int) uint64 {
 	size := cacheInitBytes + cacheGrowthBytes*uint64(epoch) - hashBytes
 	for !new(big.Int).SetUint64(size / hashBytes).ProbablyPrime(1) { // Always accurate for n < 2^64
 		size -= 2 * hashBytes
@@ -48,7 +52,10 @@ func datasetSize(block uint64) uint64 {
 	if epoch < len(datasetSizes) {
 		return datasetSizes[epoch]
 	}
-	// No known dataset size, calculate manually (sanity branch only)
+	return calcDatasetSize(epoch)
+}
+
+func calcDatasetSize(epoch int) uint64 {
 	size := datasetInitBytes + datasetGrowthBytes*uint64(epoch) - mixBytes
 	for !new(big.Int).SetUint64(size / mixBytes).ProbablyPrime(1) { // Always accurate for n < 2^64
 		size -= 2 * mixBytes

consensus/ethash/algorithm_go1.8_test.go

@@ -23,24 +23,15 @@ import "testing"
 // Tests whether the dataset size calculator works correctly by cross checking the
 // hard coded lookup table with the value generated by it.
 func TestSizeCalculations(t *testing.T) {
-	var tests []uint64
+	// Verify all the cache and dataset sizes from the lookup table.
-
+	for epoch, want := range cacheSizes {
-	// Verify all the cache sizes from the lookup table
+		if size := calcCacheSize(epoch); size != want {
-	defer func(sizes []uint64) { cacheSizes = sizes }(cacheSizes)
+			t.Errorf("cache %d: cache size mismatch: have %d, want %d", epoch, size, want)
-	tests, cacheSizes = cacheSizes, []uint64{}
-
-	for i, test := range tests {
-		if size := cacheSize(uint64(i*epochLength) + 1); size != test {
-			t.Errorf("cache %d: cache size mismatch: have %d, want %d", i, size, test)
 		}
 	}
-	// Verify all the dataset sizes from the lookup table
+	for epoch, want := range datasetSizes {
-	defer func(sizes []uint64) { datasetSizes = sizes }(datasetSizes)
+		if size := calcDatasetSize(epoch); size != want {
-	tests, datasetSizes = datasetSizes, []uint64{}
+			t.Errorf("dataset %d: dataset size mismatch: have %d, want %d", epoch, size, want)
-
-	for i, test := range tests {
-		if size := datasetSize(uint64(i*epochLength) + 1); size != test {
-			t.Errorf("dataset %d: dataset size mismatch: have %d, want %d", i, size, test)
 		}
 	}
 }

consensus/ethash/consensus.go

@@ -476,7 +476,7 @@ func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Head
 	}
 	// Sanity check that the block number is below the lookup table size (60M blocks)
 	number := header.Number.Uint64()
-	if number/epochLength >= uint64(len(cacheSizes)) {
+	if number/epochLength >= maxEpoch {
 		// Go < 1.7 cannot calculate new cache/dataset sizes (no fast prime check)
 		return errNonceOutOfRange
 	}