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// Copyright 2015 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 core
import (
"bytes"
"math/big"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"github.com/ethereum/go-ethereum/params"
"github.com/ethereum/go-ethereum/rlp"
)
var (
blockHashPre = []byte("block-hash-")
blockNumPre = []byte("block-num-")
expDiffPeriod = big.NewInt(100000)
)
// CalcDifficulty is the difficulty adjustment algorithm. It returns
// the difficulty that a new block b should have when created at time
// given the parent block's time and difficulty.
func CalcDifficulty(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
diff := new(big.Int)
adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor)
bigTime := new(big.Int)
bigParentTime := new(big.Int)
bigTime.SetUint64(time)
bigParentTime.SetUint64(parentTime)
if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
diff.Add(parentDiff, adjust)
} else {
diff.Sub(parentDiff, adjust)
}
if diff.Cmp(params.MinimumDifficulty) < 0 {
diff = params.MinimumDifficulty
}
periodCount := new(big.Int).Add(parentNumber, common.Big1)
periodCount.Div(periodCount, expDiffPeriod)
if periodCount.Cmp(common.Big1) > 0 {
// diff = diff + 2^(periodCount - 2)
expDiff := periodCount.Sub(periodCount, common.Big2)
expDiff.Exp(common.Big2, expDiff, nil)
diff.Add(diff, expDiff)
diff = common.BigMax(diff, params.MinimumDifficulty)
}
return diff
}
// CalcTD computes the total difficulty of block.
func CalcTD(block, parent *types.Block) *big.Int {
if parent == nil {
return block.Difficulty()
}
d := block.Difficulty()
d.Add(d, parent.Td)
return d
}
// CalcGasLimit computes the gas limit of the next block after parent.
// The result may be modified by the caller.
// This is miner strategy, not consensus protocol.
func CalcGasLimit(parent *types.Block) *big.Int {
// contrib = (parentGasUsed * 3 / 2) / 1024
contrib := new(big.Int).Mul(parent.GasUsed(), big.NewInt(3))
contrib = contrib.Div(contrib, big.NewInt(2))
contrib = contrib.Div(contrib, params.GasLimitBoundDivisor)
// decay = parentGasLimit / 1024 -1
decay := new(big.Int).Div(parent.GasLimit(), params.GasLimitBoundDivisor)
decay.Sub(decay, big.NewInt(1))
/*
strategy: gasLimit of block-to-mine is set based on parent's
gasUsed value. if parentGasUsed > parentGasLimit * (2/3) then we
increase it, otherwise lower it (or leave it unchanged if it's right
at that usage) the amount increased/decreased depends on how far away
from parentGasLimit * (2/3) parentGasUsed is.
*/
gl := new(big.Int).Sub(parent.GasLimit(), decay)
gl = gl.Add(gl, contrib)
gl.Set(common.BigMax(gl, params.MinGasLimit))
// however, if we're now below the target (GenesisGasLimit) we increase the
// limit as much as we can (parentGasLimit / 1024 -1)
if gl.Cmp(params.GenesisGasLimit) < 0 {
gl.Add(parent.GasLimit(), decay)
gl.Set(common.BigMin(gl, params.GenesisGasLimit))
}
return gl
}
// GetBlockByHash returns the block corresponding to the hash or nil if not found
func GetBlockByHash(db common.Database, hash common.Hash) *types.Block {
data, _ := db.Get(append(blockHashPre, hash[:]...))
if len(data) == 0 {
return nil
}
var block types.StorageBlock
if err := rlp.Decode(bytes.NewReader(data), &block); err != nil {
glog.V(logger.Error).Infof("invalid block RLP for hash %x: %v", hash, err)
return nil
}
return (*types.Block)(&block)
}
// GetBlockByHash returns the canonical block by number or nil if not found
func GetBlockByNumber(db common.Database, number uint64) *types.Block {
key, _ := db.Get(append(blockNumPre, big.NewInt(int64(number)).Bytes()...))
if len(key) == 0 {
return nil
}
return GetBlockByHash(db, common.BytesToHash(key))
}
// WriteCanonNumber writes the canonical hash for the given block
func WriteCanonNumber(db common.Database, block *types.Block) error {
key := append(blockNumPre, block.Number().Bytes()...)
err := db.Put(key, block.Hash().Bytes())
if err != nil {
return err
}
return nil
}
// WriteHead force writes the current head
func WriteHead(db common.Database, block *types.Block) error {
err := WriteCanonNumber(db, block)
if err != nil {
return err
}
err = db.Put([]byte("LastBlock"), block.Hash().Bytes())
if err != nil {
return err
}
return nil
}
// WriteBlock writes a block to the database
func WriteBlock(db common.Database, block *types.Block) error {
tstart := time.Now()
enc, _ := rlp.EncodeToBytes((*types.StorageBlock)(block))
key := append(blockHashPre, block.Hash().Bytes()...)
err := db.Put(key, enc)
if err != nil {
glog.Fatal("db write fail:", err)
return err
}
if glog.V(logger.Debug) {
glog.Infof("wrote block #%v %s. Took %v\n", block.Number(), common.PP(block.Hash().Bytes()), time.Since(tstart))
}
return nil
}
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