// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package ethash
import (
"encoding/binary"
"hash"
"math/big"
"reflect"
"runtime"
"sync"
"sync/atomic"
"time"
"unsafe"
"github.com/ava-labs/go-ethereum/common"
"github.com/ava-labs/go-ethereum/common/bitutil"
"github.com/ava-labs/go-ethereum/crypto"
"github.com/ava-labs/go-ethereum/log"
"golang.org/x/crypto/sha3"
)
const (
datasetInitBytes = 1 << 30 // Bytes in dataset at genesis
datasetGrowthBytes = 1 << 23 // Dataset growth per epoch
cacheInitBytes = 1 << 24 // Bytes in cache at genesis
cacheGrowthBytes = 1 << 17 // Cache growth per epoch
epochLength = 30000 // Blocks per epoch
mixBytes = 128 // Width of mix
hashBytes = 64 // Hash length in bytes
hashWords = 16 // Number of 32 bit ints in a hash
datasetParents = 256 // Number of parents of each dataset element
cacheRounds = 3 // Number of rounds in cache production
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)
// makeHasher creates a repetitive hasher, allowing the same hash data structures to
// be reused between hash runs instead of requiring new ones to be created. The returned
// function is not thread safe!
func makeHasher(h hash.Hash) hasher {
// sha3.state supports Read to get the sum, use it to avoid the overhead of Sum.
// Read alters the state but we reset the hash before every operation.
type readerHash interface {
hash.Hash
Read([]byte) (int, error)
}
rh, ok := h.(readerHash)
if !ok {
panic("can't find Read method on hash")
}
outputLen := rh.Size()
return func(dest []byte, data []byte) {
rh.Reset()
rh.Write(data)
rh.Read(dest[:outputLen])
}
}
// seedHash is the seed to use for generating a verification cache and the mining
// dataset.
func seedHash(block uint64) []byte {
seed := make([]byte, 32)
if block < epochLength {
return seed
}
keccak256 := makeHasher(sha3.NewLegacyKeccak256())
for i := 0; i < int(block/epochLength); i++ {
keccak256(seed, seed)
}
return seed
}
// generateCache creates a verification cache of a given size for an input seed.
// The cache production process involves first sequentially filling up 32 MB of
// memory, then performing two passes of Sergio Demian Lerner's RandMemoHash
// algor