travis, build, consensus: drop support for Go 1.7

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)