travis, build, consensus: drop support for Go 1.7

.travis.yml

@@ -3,17 +3,6 @@ go_import_path: github.com/ethereum/go-ethereum
 sudo: false
 matrix:
   include:
-    - os: linux
-      dist: trusty
-      sudo: required
-      go: 1.7.x
-      script:
-        - sudo modprobe fuse
-        - sudo chmod 666 /dev/fuse
-        - sudo chown root:$USER /etc/fuse.conf
-        - go run build/ci.go install
-        - go run build/ci.go test -coverage
-
     - os: linux
       dist: trusty
       sudo: required

build/ci.go

@@ -182,13 +182,13 @@ func doInstall(cmdline []string) {
 	// Check Go version. People regularly open issues about compilation
 	// failure with outdated Go. This should save them the trouble.
 	if !strings.Contains(runtime.Version(), "devel") {
-		// Figure out the minor version number since we can't textually compare (1.10 < 1.7)
+		// Figure out the minor version number since we can't textually compare (1.10 < 1.8)
 		var minor int
 		fmt.Sscanf(strings.TrimPrefix(runtime.Version(), "go1."), "%d", &minor)
 
-		if minor < 7 {
+		if minor < 8 {
 			log.Println("You have Go version", runtime.Version())
-			log.Println("go-ethereum requires at least Go version 1.7 and cannot")
+			log.Println("go-ethereum requires at least Go version 1.8 and cannot")
 			log.Println("be compiled with an earlier version. Please upgrade your Go installation.")
 			os.Exit(1)
 		}

consensus/ethash/algorithm.go

@@ -19,6 +19,7 @@ package ethash
 import (
 	"encoding/binary"
 	"hash"
+	"math/big"
 	"reflect"
 	"runtime"
 	"sync"
@@ -47,6 +48,48 @@ const (
 	loopAccesses       = 64      // Number of accesses in hashimoto loop
 )
 
+// cacheSize returns the size of the ethash verification cache that belongs to a certain
+// block number.
+func cacheSize(block uint64) uint64 {
+	epoch := int(block / epochLength)
+	if epoch < maxEpoch {
+		return cacheSizes[epoch]
+	}
+	return calcCacheSize(epoch)
+}
+
+// calcCacheSize calculates the cache size for epoch. The cache size grows linearly,
+// however, we always take the highest prime below the linearly growing threshold in order
+// to reduce the risk of accidental regularities leading to cyclic behavior.
+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
+	}
+	return size
+}
+
+// datasetSize returns the size of the ethash mining dataset that belongs to a certain
+// block number.
+func datasetSize(block uint64) uint64 {
+	epoch := int(block / epochLength)
+	if epoch < maxEpoch {
+		return datasetSizes[epoch]
+	}
+	return calcDatasetSize(epoch)
+}
+
+// calcDatasetSize calculates the dataset size for epoch. The dataset size grows linearly,
+// however, we always take the highest prime below the linearly growing threshold in order
+// to reduce the risk of accidental regularities leading to cyclic behavior.
+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
+	}
+	return size
+}
+
 // hasher is a repetitive hasher allowing the same hash data structures to be
 // reused between hash runs instead of requiring new ones to be created.
 type hasher func(dest []byte, data []byte)

consensus/ethash/algorithm_test.go

@@ -30,6 +30,22 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 )
 
+// 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) {
+	// Verify all the cache and dataset sizes from the lookup table.
+	for epoch, want := range cacheSizes {
+		if size := calcCacheSize(epoch); size != want {
+			t.Errorf("cache %d: cache size mismatch: have %d, want %d", epoch, size, want)
+		}
+	}
+	for epoch, want := range datasetSizes {
+		if size := calcDatasetSize(epoch); size != want {
+			t.Errorf("dataset %d: dataset size mismatch: have %d, want %d", epoch, size, want)
+		}
+	}
+}
+
 // Tests that verification caches can be correctly generated.
 func TestCacheGeneration(t *testing.T) {
 	tests := []struct {

consensus/ethash/consensus.go

@@ -53,7 +53,6 @@ var (
 	errDuplicateUncle    = errors.New("duplicate uncle")
 	errUncleIsAncestor   = errors.New("uncle is ancestor")
 	errDanglingUncle     = errors.New("uncle's parent is not ancestor")
-	errNonceOutOfRange   = errors.New("nonce out of range")
 	errInvalidDifficulty = errors.New("non-positive difficulty")
 	errInvalidMixDigest  = errors.New("invalid mix digest")
 	errInvalidPoW        = errors.New("invalid proof-of-work")
@@ -474,18 +473,13 @@ func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Head
 	if ethash.shared != nil {
 		return ethash.shared.VerifySeal(chain, header)
 	}
-	// Sanity check that the block number is below the lookup table size (60M blocks)
-	number := header.Number.Uint64()
-	if number/epochLength >= maxEpoch {
-		// Go < 1.7 cannot calculate new cache/dataset sizes (no fast prime check)
-		return errNonceOutOfRange
-	}
 	// Ensure that we have a valid difficulty for the block
 	if header.Difficulty.Sign() <= 0 {
 		return errInvalidDifficulty
 	}
-
 	// Recompute the digest and PoW value and verify against the header
+	number := header.Number.Uint64()
+
 	cache := ethash.cache(number)
 	size := datasetSize(number)
 	if ethash.config.PowMode == ModeTest {