chaincfg/blockchain: Parameterize more chain consts. (#732)

This moves several of the chain constants to the Params struct in the
chaincfg package which is intended for that purpose.  This is mostly a
backport of the same modifications made in Decred along with a few
additional things cleaned up.

The following is an overview of the changes:

- Comment all fields in the Params struct definition
- Add locals to BlockChain instance for the calculated values based on
  the provided chain params
- Rename the following param fields:
  - SubsidyHalvingInterval -> SubsidyReductionInterval
  - ResetMinDifficulty -> ReduceMinDifficulty
- Add new Param fields:
  - CoinbaseMaturity
  - TargetTimePerBlock
  - TargetTimespan
  - BlocksPerRetarget
  - RetargetAdjustmentFactor
  - MinDiffReductionTime

blockchain/chain.go

@@ -24,12 +24,6 @@ const (
 	// maxOrphanBlocks is the maximum number of orphan blocks that can be
 	// queued.
 	maxOrphanBlocks = 100
-
-	// minMemoryNodes is the minimum number of consecutive nodes needed
-	// in memory in order to perform all necessary validation.  It is used
-	// to determine when it's safe to prune nodes from memory without
-	// causing constant dynamic reloading.
-	minMemoryNodes = BlocksPerRetarget
 )
 
 // blockNode represents a block within the block chain and is primarily used to
@@ -170,6 +164,22 @@ type BlockChain struct {
 	sigCache            *txscript.SigCache
 	indexManager        IndexManager
 
+	// The following fields are calculated based upon the provided chain
+	// parameters.  They are also set when the instance is created and
+	// can't be changed afterwards, so there is no need to protect them with
+	// a separate mutex.
+	//
+	// minMemoryNodes is the minimum number of consecutive nodes needed
+	// in memory in order to perform all necessary validation.  It is used
+	// to determine when it's safe to prune nodes from memory without
+	// causing constant dynamic reloading.  This is typically the same value
+	// as blocksPerRetarget, but it is separated here for tweakability and
+	// testability.
+	minRetargetTimespan int64 // target timespan / adjustment factor
+	maxRetargetTimespan int64 // target timespan * adjustment factor
+	blocksPerRetarget   int32 // target timespan / target time per block
+	minMemoryNodes      int32
+
 	// chainLock protects concurrent access to the vast majority of the
 	// fields in this struct below this point.
 	chainLock sync.RWMutex
@@ -553,7 +563,7 @@ func (b *BlockChain) pruneBlockNodes() error {
 	// the latter loads the node and the goal is to find nodes still in
 	// memory that can be pruned.
 	newRootNode := b.bestNode
-	for i := int32(0); i < minMemoryNodes-1 && newRootNode != nil; i++ {
+	for i := int32(0); i < b.minMemoryNodes-1 && newRootNode != nil; i++ {
 		newRootNode = newRootNode.parent
 	}
 
@@ -1454,6 +1464,9 @@ func New(config *Config) (*BlockChain, error) {
 		}
 	}
 
+	targetTimespan := int64(params.TargetTimespan)
+	targetTimePerBlock := int64(params.TargetTimePerBlock)
+	adjustmentFactor := params.RetargetAdjustmentFactor
 	b := BlockChain{
 		checkpointsByHeight: checkpointsByHeight,
 		db:                  config.DB,
@@ -1462,6 +1475,10 @@ func New(config *Config) (*BlockChain, error) {
 		notifications:       config.Notifications,
 		sigCache:            config.SigCache,
 		indexManager:        config.IndexManager,
+		minRetargetTimespan: targetTimespan / adjustmentFactor,
+		maxRetargetTimespan: targetTimespan * adjustmentFactor,
+		blocksPerRetarget:   int32(targetTimespan / targetTimePerBlock),
+		minMemoryNodes:      int32(targetTimespan / targetTimePerBlock),
 		bestNode:            nil,
 		index:               make(map[chainhash.Hash]*blockNode),
 		depNodes:            make(map[chainhash.Hash][]*blockNode),

blockchain/chain_test.go

@@ -46,7 +46,7 @@ func TestHaveBlock(t *testing.T) {
 	// Since we're not dealing with the real block chain, disable
 	// checkpoints and set the coinbase maturity to 1.
 	chain.DisableCheckpoints(true)
-	blockchain.TstSetCoinbaseMaturity(1)
+	chain.TstSetCoinbaseMaturity(1)
 
 	for i := 1; i < len(blocks); i++ {
 		isOrphan, err := chain.ProcessBlock(blocks[i], blockchain.BFNone)

blockchain/common_test.go

@@ -107,10 +107,14 @@ func chainSetup(dbName string) (*blockchain.BlockChain, func(), error) {
 		}
 	}
 
+	// Copy the chain params to ensure any modifications the tests do to
+	// the chain parameters do not affect the global instance.
+	mainNetParams := chaincfg.MainNetParams
+
 	// Create the main chain instance.
 	chain, err := blockchain.New(&blockchain.Config{
 		DB:          db,
-		ChainParams: &chaincfg.MainNetParams,
+		ChainParams: &mainNetParams,
 		TimeSource:  blockchain.NewMedianTime(),
 	})
 	if err != nil {

blockchain/difficulty.go

@@ -11,37 +11,6 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 )
 
-const (
-	// targetTimespan is the desired amount of time that should elapse
-	// before block difficulty requirement is examined to determine how
-	// it should be changed in order to maintain the desired block
-	// generation rate.
-	targetTimespan = time.Hour * 24 * 14
-
-	// targetSpacing is the desired amount of time to generate each block.
-	targetSpacing = time.Minute * 10
-
-	// BlocksPerRetarget is the number of blocks between each difficulty
-	// retarget.  It is calculated based on the desired block generation
-	// rate.
-	BlocksPerRetarget = int32(targetTimespan / targetSpacing)
-
-	// retargetAdjustmentFactor is the adjustment factor used to limit
-	// the minimum and maximum amount of adjustment that can occur between
-	// difficulty retargets.
-	retargetAdjustmentFactor = 4
-
-	// minRetargetTimespan is the minimum amount of adjustment that can
-	// occur between difficulty retargets.  It equates to 25% of the
-	// previous difficulty.
-	minRetargetTimespan = int64(targetTimespan / retargetAdjustmentFactor)
-
-	// maxRetargetTimespan is the maximum amount of adjustment that can
-	// occur between difficulty retargets.  It equates to 400% of the
-	// previous difficulty.
-	maxRetargetTimespan = int64(targetTimespan * retargetAdjustmentFactor)
-)
-
 var (
 	// bigOne is 1 represented as a big.Int.  It is defined here to avoid
 	// the overhead of creating it multiple times.
@@ -190,13 +159,13 @@ func CalcWork(bits uint32) *big.Int {
 func (b *BlockChain) calcEasiestDifficulty(bits uint32, duration time.Duration) uint32 {
 	// Convert types used in the calculations below.
 	durationVal := int64(duration)
-	adjustmentFactor := big.NewInt(retargetAdjustmentFactor)
+	adjustmentFactor := big.NewInt(b.chainParams.RetargetAdjustmentFactor)
 
 	// The test network rules allow minimum difficulty blocks after more
 	// than twice the desired amount of time needed to generate a block has
 	// elapsed.
-	if b.chainParams.ResetMinDifficulty {
+	if b.chainParams.ReduceMinDifficulty {
-		if durationVal > int64(targetSpacing)*2 {
+		if durationVal > int64(b.chainParams.MinDiffReductionTime) {
 			return b.chainParams.PowLimitBits
 		}
 	}
@@ -208,7 +177,7 @@ func (b *BlockChain) calcEasiestDifficulty(bits uint32, duration time.Duration)
 	newTarget := CompactToBig(bits)
 	for durationVal > 0 && newTarget.Cmp(b.chainParams.PowLimit) < 0 {
 		newTarget.Mul(newTarget, adjustmentFactor)
-		durationVal -= maxRetargetTimespan
+		durationVal -= b.maxRetargetTimespan
 	}
 
 	// Limit new value to the proof of work limit.
@@ -227,7 +196,7 @@ func (b *BlockChain) findPrevTestNetDifficulty(startNode *blockNode) (uint32, er
 	// Search backwards through the chain for the last block without
 	// the special rule applied.
 	iterNode := startNode
-	for iterNode != nil && iterNode.height%BlocksPerRetarget != 0 &&
+	for iterNode != nil && iterNode.height%b.blocksPerRetarget != 0 &&
 		iterNode.bits == b.chainParams.PowLimitBits {
 
 		// Get the previous block node.  This function is used over
@@ -267,15 +236,15 @@ func (b *BlockChain) calcNextRequiredDifficulty(lastNode *blockNode, newBlockTim
 
 	// Return the previous block's difficulty requirements if this block
 	// is not at a difficulty retarget interval.
-	if (lastNode.height+1)%BlocksPerRetarget != 0 {
+	if (lastNode.height+1)%b.blocksPerRetarget != 0 {
-		// The test network rules allow minimum difficulty blocks after
+		// For networks that support it, allow special reduction of the
-		// more than twice the desired amount of time needed to generate
+		// required difficulty once too much time has elapsed without
-		// a block has elapsed.
+		// mining a block.
-		if b.chainParams.ResetMinDifficulty {
+		if b.chainParams.ReduceMinDifficulty {
-			// Return minimum difficulty when more than twice the
+			// Return minimum difficulty when more than the desired
-			// desired amount of time needed to generate a block has
+			// amount of time has elapsed without mining a block.
-			// elapsed.
+			reductionTime := b.chainParams.MinDiffReductionTime
-			allowMinTime := lastNode.timestamp.Add(targetSpacing * 2)
+			allowMinTime := lastNode.timestamp.Add(reductionTime)
 			if newBlockTime.After(allowMinTime) {
 				return b.chainParams.PowLimitBits, nil
 			}
@@ -298,7 +267,7 @@ func (b *BlockChain) calcNextRequiredDifficulty(lastNode *blockNode, newBlockTim
 	// Get the block node at the previous retarget (targetTimespan days
 	// worth of blocks).
 	firstNode := lastNode
-	for i := int32(0); i < BlocksPerRetarget-1 && firstNode != nil; i++ {
+	for i := int32(0); i < b.blocksPerRetarget-1 && firstNode != nil; i++ {
 		// Get the previous block node.  This function is used over
 		// simply accessing firstNode.parent directly as it will
 		// dynamically create previous block nodes as needed.  This
@@ -319,10 +288,10 @@ func (b *BlockChain) calcNextRequiredDifficulty(lastNode *blockNode, newBlockTim
 	// difficulty.
 	actualTimespan := lastNode.timestamp.UnixNano() - firstNode.timestamp.UnixNano()
 	adjustedTimespan := actualTimespan
-	if actualTimespan < minRetargetTimespan {
+	if actualTimespan < b.minRetargetTimespan {
-		adjustedTimespan = minRetargetTimespan
+		adjustedTimespan = b.minRetargetTimespan
-	} else if actualTimespan > maxRetargetTimespan {
+	} else if actualTimespan > b.maxRetargetTimespan {
-		adjustedTimespan = maxRetargetTimespan
+		adjustedTimespan = b.maxRetargetTimespan
 	}
 
 	// Calculate new target difficulty as:
@@ -332,7 +301,7 @@ func (b *BlockChain) calcNextRequiredDifficulty(lastNode *blockNode, newBlockTim
 	// result.
 	oldTarget := CompactToBig(lastNode.bits)
 	newTarget := new(big.Int).Mul(oldTarget, big.NewInt(adjustedTimespan))
-	newTarget.Div(newTarget, big.NewInt(int64(targetTimespan)))
+	newTarget.Div(newTarget, big.NewInt(int64(b.chainParams.TargetTimespan)))
 
 	// Limit new value to the proof of work limit.
 	if newTarget.Cmp(b.chainParams.PowLimit) > 0 {
@@ -349,7 +318,7 @@ func (b *BlockChain) calcNextRequiredDifficulty(lastNode *blockNode, newBlockTim
 	log.Debugf("New target %08x (%064x)", newTargetBits, CompactToBig(newTargetBits))
 	log.Debugf("Actual timespan %v, adjusted timespan %v, target timespan %v",
 		time.Duration(actualTimespan), time.Duration(adjustedTimespan),
-		targetTimespan)
+		b.chainParams.TargetTimespan)
 
 	return newTargetBits, nil
 }

blockchain/internal_test.go

@@ -19,8 +19,8 @@ import (
 
 // TstSetCoinbaseMaturity makes the ability to set the coinbase maturity
 // available to the test package.
-func TstSetCoinbaseMaturity(maturity int32) {
+func (b *BlockChain) TstSetCoinbaseMaturity(maturity uint16) {
-	coinbaseMaturity = maturity
+	b.chainParams.CoinbaseMaturity = maturity
 }
 
 // TstTimeSorter makes the internal timeSorter type available to the test

blockchain/reorganization_test.go

@@ -56,7 +56,7 @@ func TestReorganization(t *testing.T) {
 	// Since we're not dealing with the real block chain, disable
 	// checkpoints and set the coinbase maturity to 1.
 	chain.DisableCheckpoints(true)
-	blockchain.TstSetCoinbaseMaturity(1)
+	chain.TstSetCoinbaseMaturity(1)
 
 	expectedOrphans := map[int]struct{}{5: {}, 6: {}}
 	for i := 1; i < len(blocks); i++ {

blockchain/validate.go

@@ -45,18 +45,9 @@ const (
 	// baseSubsidy is the starting subsidy amount for mined blocks.  This
 	// value is halved every SubsidyHalvingInterval blocks.
 	baseSubsidy = 50 * btcutil.SatoshiPerBitcoin
-
-	// CoinbaseMaturity is the number of blocks required before newly
-	// mined bitcoins (coinbase transactions) can be spent.
-	CoinbaseMaturity = 100
 )
 
 var (
-	// coinbaseMaturity is the internal variable used for validating the
-	// spending of coinbase outputs.  A variable rather than the exported
-	// constant is used because the tests need the ability to modify it.
-	coinbaseMaturity = int32(CoinbaseMaturity)
-
 	// zeroHash is the zero value for a chainhash.Hash and is defined as
 	// a package level variable to avoid the need to create a new instance
 	// every time a check is needed.
@@ -182,18 +173,18 @@ func isBIP0030Node(node *blockNode) bool {
 // newly generated blocks awards as well as validating the coinbase for blocks
 // has the expected value.
 //
-// The subsidy is halved every SubsidyHalvingInterval blocks.  Mathematically
+// The subsidy is halved every SubsidyReductionInterval blocks.  Mathematically
-// this is: baseSubsidy / 2^(height/subsidyHalvingInterval)
+// this is: baseSubsidy / 2^(height/SubsidyReductionInterval)
 //
 // At the target block generation rate for the main network, this is
 // approximately every 4 years.
 func CalcBlockSubsidy(height int32, chainParams *chaincfg.Params) int64 {
-	if chainParams.SubsidyHalvingInterval == 0 {
+	if chainParams.SubsidyReductionInterval == 0 {
 		return baseSubsidy
 	}
 
 	// Equivalent to: baseSubsidy / 2^(height/subsidyHalvingInterval)
-	return baseSubsidy >> uint(height/chainParams.SubsidyHalvingInterval)
+	return baseSubsidy >> uint(height/chainParams.SubsidyReductionInterval)
 }
 
 // CheckTransactionSanity performs some preliminary checks on a transaction to
@@ -833,7 +824,7 @@ func (b *BlockChain) checkBIP0030(node *blockNode, block *btcutil.Block, view *U
 //
 // NOTE: The transaction MUST have already been sanity checked with the
 // CheckTransactionSanity function prior to calling this function.
-func CheckTransactionInputs(tx *btcutil.Tx, txHeight int32, utxoView *UtxoViewpoint) (int64, error) {
+func CheckTransactionInputs(tx *btcutil.Tx, txHeight int32, utxoView *UtxoViewpoint, chainParams *chaincfg.Params) (int64, error) {
 	// Coinbase transactions have no inputs.
 	if IsCoinBase(tx) {
 		return 0, nil
@@ -857,6 +848,7 @@ func CheckTransactionInputs(tx *btcutil.Tx, txHeight int32, utxoView *UtxoViewpo
 		if utxoEntry.IsCoinBase() {
 			originHeight := int32(utxoEntry.BlockHeight())
 			blocksSincePrev := txHeight - originHeight
+			coinbaseMaturity := int32(chainParams.CoinbaseMaturity)
 			if blocksSincePrev < coinbaseMaturity {
 				str := fmt.Sprintf("tried to spend coinbase "+
 					"transaction %v from height %v at "+
@@ -1050,7 +1042,8 @@ func (b *BlockChain) checkConnectBlock(node *blockNode, block *btcutil.Block, vi
 	// bounds.
 	var totalFees int64
 	for _, tx := range transactions {
-		txFee, err := CheckTransactionInputs(tx, node.height, view)
+		txFee, err := CheckTransactionInputs(tx, node.height, view,
+			b.chainParams)
 		if err != nil {
 			return err
 		}

chaincfg/params.go

@@ -7,6 +7,7 @@ package chaincfg
 import (
 	"errors"
 	"math/big"
+	"time"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
@@ -53,18 +54,69 @@ type Checkpoint struct {
 // used by Bitcoin applications to differentiate networks as well as addresses
 // and keys for one network from those intended for use on another network.
 type Params struct {
+	// Name defines a human-readable identifier for the network.
 	Name string
+
+	// Net defines the magic bytes used to identify the network.
 	Net wire.BitcoinNet
+
+	// DefaultPort defines the default peer-to-peer port for the network.
 	DefaultPort string
+
+	// DNSSeeds defines a list of DNS seeds for the network that are used
+	// as one method to discover peers.
 	DNSSeeds []string
 
-	// Chain parameters
+	// GenesisBlock defines the first block of the chain.
 	GenesisBlock *wire.MsgBlock
+
+	// GenesisHash is the starting block hash.
 	GenesisHash *chainhash.Hash
+
+	// PowLimit defines the highest allowed proof of work value for a block
+	// as a uint256.
 	PowLimit *big.Int
+
+	// PowLimitBits defines the highest allowed proof of work value for a
+	// block in compact form.
 	PowLimitBits uint32
-	SubsidyHalvingInterval int32
+
-	ResetMinDifficulty     bool
+	// CoinbaseMaturity is the number of blocks required before newly mined
+	// coins (coinbase transactions) can be spent.
+	CoinbaseMaturity uint16
+
+	// SubsidyReductionInterval is the interval of blocks before the subsidy
+	// is reduced.
+	SubsidyReductionInterval int32
+
+	// TargetTimespan is the desired amount of time that should elapse
+	// before the block difficulty requirement is examined to determine how
+	// it should be changed in order to maintain the desired block
+	// generation rate.
+	TargetTimespan time.Duration
+
+	// TargetTimePerBlock is the desired amount of time to generate each
+	// block.
+	TargetTimePerBlock time.Duration
+
+	// RetargetAdjustmentFactor is the adjustment factor used to limit
+	// the minimum and maximum amount of adjustment that can occur between
+	// difficulty retargets.
+	RetargetAdjustmentFactor int64
+
+	// ReduceMinDifficulty defines whether the network should reduce the
+	// minimum required difficulty after a long enough period of time has
+	// passed without finding a block.  This is really only useful for test
+	// networks and should not be set on a main network.
+	ReduceMinDifficulty bool
+
+	// MinDiffReductionTime is the amount of time after which the minimum
+	// required difficulty should be reduced when a block hasn't been found.
+	//
+	// NOTE: This only applies if ReduceMinDifficulty is true.
+	MinDiffReductionTime time.Duration
+
+	// GenerateSupported specifies whether or not CPU mining is allowed.
 	GenerateSupported bool
 
 	// Checkpoints ordered from oldest to newest.
@@ -118,8 +170,13 @@ var MainNetParams = Params{
 	GenesisHash:              &genesisHash,
 	PowLimit:                 mainPowLimit,
 	PowLimitBits:             0x1d00ffff,
-	SubsidyHalvingInterval: 210000,
+	CoinbaseMaturity:         100,
-	ResetMinDifficulty:     false,
+	SubsidyReductionInterval: 210000,
+	TargetTimespan:           time.Hour * 24 * 14, // 14 days
+	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
+	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
+	ReduceMinDifficulty:      false,
+	MinDiffReductionTime:     0,
 	GenerateSupported:        false,
 
 	// Checkpoints ordered from oldest to newest.
@@ -185,8 +242,13 @@ var RegressionNetParams = Params{
 	GenesisHash:              &regTestGenesisHash,
 	PowLimit:                 regressionPowLimit,
 	PowLimitBits:             0x207fffff,
-	SubsidyHalvingInterval: 150,
+	CoinbaseMaturity:         100,
-	ResetMinDifficulty:     true,
+	SubsidyReductionInterval: 150,
+	TargetTimespan:           time.Hour * 24 * 14, // 14 days
+	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
+	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
+	ReduceMinDifficulty:      true,
+	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
 	GenerateSupported:        true,
 
 	// Checkpoints ordered from oldest to newest.
@@ -237,8 +299,13 @@ var TestNet3Params = Params{
 	GenesisHash:              &testNet3GenesisHash,
 	PowLimit:                 testNet3PowLimit,
 	PowLimitBits:             0x1d00ffff,
-	SubsidyHalvingInterval: 210000,
+	CoinbaseMaturity:         100,
-	ResetMinDifficulty:     true,
+	SubsidyReductionInterval: 210000,
+	TargetTimespan:           time.Hour * 24 * 14, // 14 days
+	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
+	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
+	ReduceMinDifficulty:      true,
+	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
 	GenerateSupported:        false,
 
 	// Checkpoints ordered from oldest to newest.
@@ -291,8 +358,13 @@ var SimNetParams = Params{
 	GenesisHash:              &simNetGenesisHash,
 	PowLimit:                 simNetPowLimit,
 	PowLimitBits:             0x207fffff,
-	SubsidyHalvingInterval: 210000,
+	CoinbaseMaturity:         100,
-	ResetMinDifficulty:     true,
+	SubsidyReductionInterval: 210000,
+	TargetTimespan:           time.Hour * 24 * 14, // 14 days
+	TargetTimePerBlock:       time.Minute * 10,    // 10 minutes
+	RetargetAdjustmentFactor: 4,                   // 25% less, 400% more
+	ReduceMinDifficulty:      true,
+	MinDiffReductionTime:     time.Minute * 20, // TargetTimePerBlock * 2
 	GenerateSupported:        true,
 
 	// Checkpoints ordered from oldest to newest.

mempool.go

@@ -596,7 +596,7 @@ func (mp *txMemPool) maybeAcceptTransaction(tx *btcutil.Tx, isNew, rateLimit boo
 	// Also returns the fees associated with the transaction which will be
 	// used later.
 	txFee, err := blockchain.CheckTransactionInputs(tx, nextBlockHeight,
-		utxoView)
+		utxoView, activeNetParams.Params)
 	if err != nil {
 		if cerr, ok := err.(blockchain.RuleError); ok {
 			return nil, chainRuleError(cerr)

mining.go

@@ -651,7 +651,7 @@ mempoolLoop:
 		// Ensure the transaction inputs pass all of the necessary
 		// preconditions before allowing it to be added to the block.
 		_, err = blockchain.CheckTransactionInputs(tx, nextBlockHeight,
-			blockUtxos)
+			blockUtxos, activeNetParams.Params)
 		if err != nil {
 			minrLog.Tracef("Skipping tx %s due to error in "+
 				"CheckTransactionInputs: %v", tx.Hash(), err)
@@ -781,7 +781,7 @@ func UpdateBlockTime(msgBlock *wire.MsgBlock, bManager *blockManager) error {
 
 	// If running on a network that requires recalculating the difficulty,
 	// do so now.
-	if activeNetParams.ResetMinDifficulty {
+	if activeNetParams.ReduceMinDifficulty {
 		difficulty, err := bManager.chain.CalcNextRequiredDifficulty(
 			newTimestamp)
 		if err != nil {

rpcserver.go

@@ -2104,6 +2104,11 @@ func handleGetNetworkHashPS(s *rpcServer, cmd interface{}, closeChan <-chan stru
 		endHeight = best.Height
 	}
 
+	// Calculate the number of blocks per retarget interval based on the
+	// chain parameters.
+	blocksPerRetarget := int32(s.server.chainParams.TargetTimespan /
+		s.server.chainParams.TargetTimePerBlock)
+
 	// Calculate the starting block height based on the passed number of
 	// blocks.  When the passed value is negative, use the last block the
 	// difficulty changed as the starting height.  Also make sure the
@@ -2114,7 +2119,7 @@ func handleGetNetworkHashPS(s *rpcServer, cmd interface{}, closeChan <-chan stru
 	}
 	var startHeight int32
 	if numBlocks <= 0 {
-		startHeight = endHeight - ((endHeight % blockchain.BlocksPerRetarget) + 1)
+		startHeight = endHeight - ((endHeight % blocksPerRetarget) + 1)
 	} else {
 		startHeight = endHeight - numBlocks
 	}