diff --git a/blockchain/chain.go b/blockchain/chain.go
index 7e06e5c77c..8e75b447e9 100644
--- a/blockchain/chain.go
+++ b/blockchain/chain.go
@@ -1798,6 +1798,144 @@ func (b *BlockChain) LocateHeaders(locator BlockLocator, hashStop *chainhash.Has
 	return headers
 }
 
+// InvalidateBlock invalidates the requested block and all its descedents.  If a block
+// in the best chain is invalidated, the active chain tip will be the parent of the
+// invalidated block.
+//
+// This function is safe for concurrent access.
+func (b *BlockChain) InvalidateBlock(hash *chainhash.Hash) error {
+	b.chainLock.Lock()
+	defer b.chainLock.Unlock()
+
+	node := b.index.LookupNode(hash)
+	if node == nil {
+		// Return an error if the block doesn't exist.
+		return fmt.Errorf("Requested block hash of %s is not found "+
+			"and thus cannot be invalidated.", hash)
+	}
+	if node.height == 0 {
+		return fmt.Errorf("Requested block hash of %s is a at height 0 "+
+			"and is thus a genesis block and cannot be invalidated.",
+			node.hash)
+	}
+
+	// Nothing to do if the given block is already invalid.
+	if node.status.KnownInvalid() {
+		return nil
+	}
+
+	// Set the status of the block being invalidated.
+	b.index.SetStatusFlags(node, statusValidateFailed)
+	b.index.UnsetStatusFlags(node, statusValid)
+
+	// If the block we're invalidating is not on the best chain, we simply
+	// mark the block and all its descendants as invalid and return.
+	if !b.bestChain.Contains(node) {
+		// Grab all the tips excluding the active tip.
+		tips := b.index.InactiveTips(b.bestChain)
+		for _, tip := range tips {
+			// Continue if the given inactive tip is not a descendant of the block
+			// being invalidated.
+			if !tip.IsAncestor(node) {
+				continue
+			}
+
+			// Keep going back until we get to the block being invalidated.
+			// For each of the parent, we'll unset valid status and set invalid
+			// ancestor status.
+			for n := tip; n != nil && n != node; n = n.parent {
+				// Continue if it's already invalid.
+				if n.status.KnownInvalid() {
+					continue
+				}
+				b.index.SetStatusFlags(n, statusInvalidAncestor)
+				b.index.UnsetStatusFlags(n, statusValid)
+			}
+		}
+
+		if writeErr := b.index.flushToDB(); writeErr != nil {
+			return fmt.Errorf("Error flushing block index "+
+				"changes to disk: %v", writeErr)
+		}
+
+		// Return since the block being invalidated is on a side branch.
+		// Nothing else left to do.
+		return nil
+	}
+
+	// If we're here, it means a block from the active chain tip is getting
+	// invalidated.
+	//
+	// Grab all the nodes to detach from the active chain.
+	detachNodes := list.New()
+	for n := b.bestChain.Tip(); n != nil && n != node; n = n.parent {
+		// Continue if it's already invalid.
+		if n.status.KnownInvalid() {
+			continue
+		}
+
+		// Change the status of the block node.
+		b.index.SetStatusFlags(n, statusInvalidAncestor)
+		b.index.UnsetStatusFlags(n, statusValid)
+		detachNodes.PushBack(n)
+	}
+
+	// Push back the block node being invalidated.
+	detachNodes.PushBack(node)
+
+	// Reorg back to the parent of the block being invalidated.
+	// Nothing to attach so just pass an empty list.
+	err := b.reorganizeChain(detachNodes, list.New())
+	if err != nil {
+		return err
+	}
+
+	if writeErr := b.index.flushToDB(); writeErr != nil {
+		log.Warnf("Error flushing block index changes to disk: %v", writeErr)
+	}
+
+	// Grab all the tips.
+	tips := b.index.InactiveTips(b.bestChain)
+	tips = append(tips, b.bestChain.Tip())
+
+	// Here we'll check if the invalidation of the block in the active tip
+	// changes the status of the chain tips.  If a side branch now has more
+	// worksum, it becomes the active chain tip.
+	var bestTip *blockNode
+	for _, tip := range tips {
+		// Skip invalid tips as they cannot become the active tip.
+		if tip.status.KnownInvalid() {
+			continue
+		}
+
+		// If we have no best tips, then set this tip as the best tip.
+		if bestTip == nil {
+			bestTip = tip
+		} else {
+			// If there is an existing best tip, then compare it
+			// against the current tip.
+			if tip.workSum.Cmp(bestTip.workSum) == 1 {
+				bestTip = tip
+			}
+		}
+	}
+
+	// Return if the best tip is the current tip.
+	if bestTip == b.bestChain.Tip() {
+		return nil
+	}
+
+	// Reorganize to the best tip if a side branch is now the most work tip.
+	detachNodes, attachNodes := b.getReorganizeNodes(bestTip)
+	err = b.reorganizeChain(detachNodes, attachNodes)
+
+	if writeErr := b.index.flushToDB(); writeErr != nil {
+		log.Warnf("Error flushing block index changes to disk: %v", writeErr)
+	}
+
+	return err
+}
+
 // IndexManager provides a generic interface that the is called when blocks are
 // connected and disconnected to and from the tip of the main chain for the
 // purpose of supporting optional indexes.
diff --git a/blockchain/chain_test.go b/blockchain/chain_test.go
index 259a643f3c..57bbd6246c 100644
--- a/blockchain/chain_test.go
+++ b/blockchain/chain_test.go
@@ -6,10 +6,12 @@ package blockchain
 
 import (
 	"fmt"
+	"math/rand"
 	"reflect"
 	"testing"
 	"time"
 
+	"github.com/btcsuite/btcd/blockchain/internal/testhelper"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -1311,3 +1313,312 @@ func TestIsAncestor(t *testing.T) {
 			branch2Nodes[0].hash.String())
 	}
 }
+
+// randomSelect selects random amount of random elements from a slice and returns a
+// new slice.  The selected elements are removed.
+func randomSelect(input []*testhelper.SpendableOut) (
+	[]*testhelper.SpendableOut, []*testhelper.SpendableOut) {
+
+	selected := []*testhelper.SpendableOut{}
+
+	// Select random elements from the input slice
+	amount := rand.Intn(len(input))
+	for i := 0; i < amount; i++ {
+		// Generate a random index
+		randIdx := rand.Intn(len(input))
+
+		// Append the selected element to the new slice
+		selected = append(selected, input[randIdx])
+
+		// Remove the selected element from the input slice.
+		// This ensures that each selected element is unique.
+		input = append(input[:randIdx], input[randIdx+1:]...)
+	}
+
+	return input, selected
+}
+
+// addBlocks generates new blocks and adds them to the chain.  The newly generated
+// blocks will spend from the spendable outputs passed in.  The returned hases are
+// the hashes of the newly generated blocks.
+func addBlocks(count int, chain *BlockChain, prevBlock *btcutil.Block,
+	allSpendableOutputs []*testhelper.SpendableOut) (
+	[]*chainhash.Hash, [][]*testhelper.SpendableOut, error) {
+
+	blockHashes := make([]*chainhash.Hash, 0, count)
+	spendablesOuts := make([][]*testhelper.SpendableOut, 0, count)
+
+	// Always spend everything on the first block.  This ensures we get unique blocks
+	// every time.  The random select may choose not to spend any and that results
+	// in getting the same block.
+	nextSpends := allSpendableOutputs
+	allSpendableOutputs = allSpendableOutputs[:0]
+	for b := 0; b < count; b++ {
+		newBlock, newSpendableOuts, err := addBlock(chain, prevBlock, nextSpends)
+		if err != nil {
+			return nil, nil, err
+		}
+		prevBlock = newBlock
+
+		blockHashes = append(blockHashes, newBlock.Hash())
+		spendablesOuts = append(spendablesOuts, newSpendableOuts)
+		allSpendableOutputs = append(allSpendableOutputs, newSpendableOuts...)
+
+		// Grab utxos to be spent in the next block.
+		allSpendableOutputs, nextSpends = randomSelect(allSpendableOutputs)
+	}
+
+	return blockHashes, spendablesOuts, nil
+}
+
+func TestInvalidateBlock(t *testing.T) {
+	tests := []struct {
+		name     string
+		chainGen func() (*BlockChain, []*chainhash.Hash, func())
+	}{
+		{
+			name: "one branch, invalidate once",
+			chainGen: func() (*BlockChain, []*chainhash.Hash, func()) {
+				chain, params, tearDown := utxoCacheTestChain(
+					"TestInvalidateBlock-one-branch-" +
+						"invalidate-once")
+				// Grab the tip of the chain.
+				tip := btcutil.NewBlock(params.GenesisBlock)
+
+				// Create a chain with 11 blocks.
+				_, _, err := addBlocks(11, chain, tip, []*testhelper.SpendableOut{})
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Invalidate block 5.
+				block, err := chain.BlockByHeight(5)
+				if err != nil {
+					t.Fatal(err)
+				}
+				invalidateHash := block.Hash()
+
+				return chain, []*chainhash.Hash{invalidateHash}, tearDown
+			},
+		},
+		{
+			name: "invalidate twice",
+			chainGen: func() (*BlockChain, []*chainhash.Hash, func()) {
+				chain, params, tearDown := utxoCacheTestChain("TestInvalidateBlock-invalidate-twice")
+				// Grab the tip of the chain.
+				tip := btcutil.NewBlock(params.GenesisBlock)
+
+				// Create a chain with 11 blocks.
+				_, spendableOuts, err := addBlocks(11, chain, tip, []*testhelper.SpendableOut{})
+				//_, _, err := addBlocks(11, chain, tip, []*testhelper.SpendableOut{})
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Set invalidateHash as block 5.
+				block, err := chain.BlockByHeight(5)
+				if err != nil {
+					t.Fatal(err)
+				}
+				invalidateHash := block.Hash()
+
+				// Create a side chain with 7 blocks that builds on block 1.
+				b1, err := chain.BlockByHeight(1)
+				if err != nil {
+					t.Fatal(err)
+				}
+				altBlockHashes, _, err := addBlocks(6, chain, b1, spendableOuts[0])
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Grab block at height 5:
+				//
+				// b2, b3, b4, b5
+				//  0,  1,  2,  3
+				invalidateHash2 := altBlockHashes[3]
+
+				// Sanity checking that we grabbed the correct hash.
+				node := chain.index.LookupNode(invalidateHash)
+				if node == nil || node.height != 5 {
+					t.Fatalf("wanted to grab block at height 5 but got height %v",
+						node.height)
+				}
+
+				return chain, []*chainhash.Hash{invalidateHash, invalidateHash2}, tearDown
+			},
+		},
+		{
+			name: "invalidate a side branch",
+			chainGen: func() (*BlockChain, []*chainhash.Hash, func()) {
+				chain, params, tearDown := utxoCacheTestChain("TestInvalidateBlock-invalidate-side-branch")
+				tip := btcutil.NewBlock(params.GenesisBlock)
+
+				// Grab the tip of the chain.
+				tip, err := chain.BlockByHash(&chain.bestChain.Tip().hash)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Create a chain with 11 blocks.
+				_, spendableOuts, err := addBlocks(11, chain, tip, []*testhelper.SpendableOut{})
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Create a side chain with 7 blocks that builds on block 1.
+				b1, err := chain.BlockByHeight(1)
+				if err != nil {
+					t.Fatal(err)
+				}
+				altBlockHashes, _, err := addBlocks(6, chain, b1, spendableOuts[0])
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				// Grab block at height 4:
+				//
+				// b2, b3, b4
+				//  0,  1,  2
+				invalidateHash := altBlockHashes[2]
+
+				// Sanity checking that we grabbed the correct hash.
+				node := chain.index.LookupNode(invalidateHash)
+				if node == nil || node.height != 4 {
+					t.Fatalf("wanted to grab block at height 4 but got height %v",
+						node.height)
+				}
+
+				return chain, []*chainhash.Hash{invalidateHash}, tearDown
+			},
+		},
+	}
+
+	for _, test := range tests {
+		chain, invalidateHashes, tearDown := test.chainGen()
+		func() {
+			defer tearDown()
+			for _, invalidateHash := range invalidateHashes {
+				chainTipsBefore := chain.ChainTips()
+
+				// Mark if we're invalidating a block that's a part of the best chain.
+				var bestChainBlock bool
+				node := chain.index.LookupNode(invalidateHash)
+				if chain.bestChain.Contains(node) {
+					bestChainBlock = true
+				}
+
+				// Actual invalidation.
+				err := chain.InvalidateBlock(invalidateHash)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				chainTipsAfter := chain.ChainTips()
+
+				// Create a map for easy lookup.
+				chainTipMap := make(map[chainhash.Hash]ChainTip, len(chainTipsAfter))
+				activeTipCount := 0
+				for _, chainTip := range chainTipsAfter {
+					chainTipMap[chainTip.BlockHash] = chainTip
+
+					if chainTip.Status == StatusActive {
+						activeTipCount++
+					}
+				}
+				if activeTipCount != 1 {
+					t.Fatalf("TestInvalidateBlock fail. Expected "+
+						"1 active chain tip but got %d", activeTipCount)
+				}
+
+				bestTip := chain.bestChain.Tip()
+
+				validForkCount := 0
+				for _, tip := range chainTipsBefore {
+					// If the chaintip was an active tip and we invalidated a block
+					// in the active tip, assert that it's invalid now.
+					if bestChainBlock && tip.Status == StatusActive {
+						gotTip, found := chainTipMap[tip.BlockHash]
+						if !found {
+							t.Fatalf("TestInvalidateBlock fail. Expected "+
+								"block %s not found in chaintips after "+
+								"invalidateblock", tip.BlockHash.String())
+						}
+
+						if gotTip.Status != StatusInvalid {
+							t.Fatalf("TestInvalidateBlock fail. "+
+								"Expected block %s to be invalid, got status: %s",
+								gotTip.BlockHash.String(), gotTip.Status)
+						}
+					}
+
+					if !bestChainBlock && tip.Status != StatusActive {
+						gotTip, found := chainTipMap[tip.BlockHash]
+						if !found {
+							t.Fatalf("TestInvalidateBlock fail. Expected "+
+								"block %s not found in chaintips after "+
+								"invalidateblock", tip.BlockHash.String())
+						}
+
+						if gotTip.BlockHash == *invalidateHash && gotTip.Status != StatusInvalid {
+							t.Fatalf("TestInvalidateBlock fail. "+
+								"Expected block %s to be invalid, got status: %s",
+								gotTip.BlockHash.String(), gotTip.Status)
+						}
+					}
+
+					// If we're not invalidating the branch with an active tip,
+					// we expect the active tip to remain the same.
+					if !bestChainBlock && tip.Status == StatusActive && tip.BlockHash != bestTip.hash {
+						t.Fatalf("TestInvalidateBlock fail. Expected block %s as the tip but got %s",
+							tip.BlockHash.String(), bestTip.hash.String())
+					}
+
+					// If this tip is not invalid and not active, it should be
+					// lighter than the current best tip.
+					if tip.Status != StatusActive && tip.Status != StatusInvalid &&
+						tip.Height > bestTip.height {
+
+						tipNode := chain.index.LookupNode(&tip.BlockHash)
+						if bestTip.workSum.Cmp(tipNode.workSum) == -1 {
+							t.Fatalf("TestInvalidateBlock fail. Expected "+
+								"block %s to be the active tip but block %s "+
+								"was", tipNode.hash.String(), bestTip.hash.String())
+						}
+					}
+
+					if tip.Status == StatusValidFork {
+						validForkCount++
+					}
+				}
+
+				// If there are no other valid chain tips besides the active chaintip,
+				// we expect to have one more chain tip after the invalidate.
+				if validForkCount == 0 && len(chainTipsAfter) != len(chainTipsBefore)+1 {
+					t.Fatalf("TestInvalidateBlock fail. Expected %d chaintips but got %d",
+						len(chainTipsBefore)+1, len(chainTipsAfter))
+				}
+			}
+
+			// Try to invaliate the already invalidated hash.
+			err := chain.InvalidateBlock(invalidateHashes[0])
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// Try to invaliate a genesis block
+			err = chain.InvalidateBlock(chain.chainParams.GenesisHash)
+			if err == nil {
+				t.Fatalf("TestInvalidateBlock fail. Expected to err when trying to" +
+					"invalidate a genesis block.")
+			}
+
+			// Try to invaliate a block that doesn't exist.
+			err = chain.InvalidateBlock(chaincfg.MainNetParams.GenesisHash)
+			if err == nil {
+				t.Fatalf("TestInvalidateBlock fail. Expected to err when trying to" +
+					"invalidate a block that doesn't exist.")
+			}
+		}()
+	}
+}
diff --git a/blockchain/common_test.go b/blockchain/common_test.go
index 5037c1828e..12badd3ec0 100644
--- a/blockchain/common_test.go
+++ b/blockchain/common_test.go
@@ -14,6 +14,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/btcsuite/btcd/blockchain/internal/testhelper"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -396,3 +397,96 @@ func newFakeNode(parent *blockNode, blockVersion int32, bits uint32, timestamp t
 	}
 	return newBlockNode(header, parent)
 }
+
+// addBlock adds a block to the blockchain that succeeds the previous block.
+// The blocks spends all the provided spendable outputs.  The new block and
+// the new spendable outputs created in the block are returned.
+func addBlock(chain *BlockChain, prev *btcutil.Block, spends []*testhelper.SpendableOut) (
+	*btcutil.Block, []*testhelper.SpendableOut, error) {
+
+	block, outs, err := newBlock(chain, prev, spends)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	_, _, err = chain.ProcessBlock(block, BFNone)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return block, outs, nil
+}
+
+// calcMerkleRoot creates a merkle tree from the slice of transactions and
+// returns the root of the tree.
+func calcMerkleRoot(txns []*wire.MsgTx) chainhash.Hash {
+	if len(txns) == 0 {
+		return chainhash.Hash{}
+	}
+
+	utilTxns := make([]*btcutil.Tx, 0, len(txns))
+	for _, tx := range txns {
+		utilTxns = append(utilTxns, btcutil.NewTx(tx))
+	}
+	return CalcMerkleRoot(utilTxns, false)
+}
+
+// newBlock creates a block to the blockchain that succeeds the previous block.
+// The blocks spends all the provided spendable outputs.  The new block and the
+// newly spendable outputs created in the block are returned.
+func newBlock(chain *BlockChain, prev *btcutil.Block,
+	spends []*testhelper.SpendableOut) (*btcutil.Block, []*testhelper.SpendableOut, error) {
+
+	blockHeight := prev.Height() + 1
+	txns := make([]*wire.MsgTx, 0, 1+len(spends))
+
+	// Create and add coinbase tx.
+	cb := testhelper.CreateCoinbaseTx(blockHeight, CalcBlockSubsidy(blockHeight, chain.chainParams))
+	txns = append(txns, cb)
+
+	// Spend all txs to be spent.
+	for _, spend := range spends {
+		cb.TxOut[0].Value += int64(testhelper.LowFee)
+
+		spendTx := testhelper.CreateSpendTx(spend, testhelper.LowFee)
+		txns = append(txns, spendTx)
+	}
+
+	// Use a timestamp that is one second after the previous block unless
+	// this is the first block in which case the current time is used.
+	var ts time.Time
+	if blockHeight == 1 {
+		ts = time.Unix(time.Now().Unix(), 0)
+	} else {
+		ts = prev.MsgBlock().Header.Timestamp.Add(time.Second)
+	}
+
+	// Create the block. The nonce will be solved in the below code in
+	// SolveBlock.
+	block := btcutil.NewBlock(&wire.MsgBlock{
+		Header: wire.BlockHeader{
+			Version:    1,
+			PrevBlock:  *prev.Hash(),
+			MerkleRoot: calcMerkleRoot(txns),
+			Bits:       chain.chainParams.PowLimitBits,
+			Timestamp:  ts,
+			Nonce:      0, // To be solved.
+		},
+		Transactions: txns,
+	})
+	block.SetHeight(blockHeight)
+
+	// Solve the block.
+	if !testhelper.SolveBlock(&block.MsgBlock().Header) {
+		return nil, nil, fmt.Errorf("Unable to solve block at height %d", blockHeight)
+	}
+
+	// Create spendable outs to return.
+	outs := make([]*testhelper.SpendableOut, len(txns))
+	for i, tx := range txns {
+		out := testhelper.MakeSpendableOutForTx(tx, 0)
+		outs[i] = &out
+	}
+
+	return block, outs, nil
+}
diff --git a/blockchain/difficulty.go b/blockchain/difficulty.go
index 1fa850cc37..b1e39b9d62 100644
--- a/blockchain/difficulty.go
+++ b/blockchain/difficulty.go
@@ -8,31 +8,14 @@ import (
 	"math/big"
 	"time"
 
+	"github.com/btcsuite/btcd/blockchain/internal/workmath"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 )
 
-var (
-	// bigOne is 1 represented as a big.Int.  It is defined here to avoid
-	// the overhead of creating it multiple times.
-	bigOne = big.NewInt(1)
-
-	// oneLsh256 is 1 shifted left 256 bits.  It is defined here to avoid
-	// the overhead of creating it multiple times.
-	oneLsh256 = new(big.Int).Lsh(bigOne, 256)
-)
-
 // HashToBig converts a chainhash.Hash into a big.Int that can be used to
 // perform math comparisons.
 func HashToBig(hash *chainhash.Hash) *big.Int {
-	// A Hash is in little-endian, but the big package wants the bytes in
-	// big-endian, so reverse them.
-	buf := *hash
-	blen := len(buf)
-	for i := 0; i < blen/2; i++ {
-		buf[i], buf[blen-1-i] = buf[blen-1-i], buf[i]
-	}
-
-	return new(big.Int).SetBytes(buf[:])
+	return workmath.HashToBig(hash)
 }
 
 // CompactToBig converts a compact representation of a whole number N to an
@@ -60,31 +43,7 @@ func HashToBig(hash *chainhash.Hash) *big.Int {
 // which represent difficulty targets, thus there really is not a need for a
 // sign bit, but it is implemented here to stay consistent with bitcoind.
 func CompactToBig(compact uint32) *big.Int {
-	// Extract the mantissa, sign bit, and exponent.
-	mantissa := compact & 0x007fffff
-	isNegative := compact&0x00800000 != 0
-	exponent := uint(compact >> 24)
-
-	// Since the base for the exponent is 256, the exponent can be treated
-	// as the number of bytes to represent the full 256-bit number.  So,
-	// treat the exponent as the number of bytes and shift the mantissa
-	// right or left accordingly.  This is equivalent to:
-	// N = mantissa * 256^(exponent-3)
-	var bn *big.Int
-	if exponent <= 3 {
-		mantissa >>= 8 * (3 - exponent)
-		bn = big.NewInt(int64(mantissa))
-	} else {
-		bn = big.NewInt(int64(mantissa))
-		bn.Lsh(bn, 8*(exponent-3))
-	}
-
-	// Make it negative if the sign bit is set.
-	if isNegative {
-		bn = bn.Neg(bn)
-	}
-
-	return bn
+	return workmath.CompactToBig(compact)
 }
 
 // BigToCompact converts a whole number N to a compact representation using
@@ -92,41 +51,7 @@ func CompactToBig(compact uint32) *big.Int {
 // of precision, so values larger than (2^23 - 1) only encode the most
 // significant digits of the number.  See CompactToBig for details.
 func BigToCompact(n *big.Int) uint32 {
-	// No need to do any work if it's zero.
-	if n.Sign() == 0 {
-		return 0
-	}
-
-	// Since the base for the exponent is 256, the exponent can be treated
-	// as the number of bytes.  So, shift the number right or left
-	// accordingly.  This is equivalent to:
-	// mantissa = mantissa / 256^(exponent-3)
-	var mantissa uint32
-	exponent := uint(len(n.Bytes()))
-	if exponent <= 3 {
-		mantissa = uint32(n.Bits()[0])
-		mantissa <<= 8 * (3 - exponent)
-	} else {
-		// Use a copy to avoid modifying the caller's original number.
-		tn := new(big.Int).Set(n)
-		mantissa = uint32(tn.Rsh(tn, 8*(exponent-3)).Bits()[0])
-	}
-
-	// When the mantissa already has the sign bit set, the number is too
-	// large to fit into the available 23-bits, so divide the number by 256
-	// and increment the exponent accordingly.
-	if mantissa&0x00800000 != 0 {
-		mantissa >>= 8
-		exponent++
-	}
-
-	// Pack the exponent, sign bit, and mantissa into an unsigned 32-bit
-	// int and return it.
-	compact := uint32(exponent<<24) | mantissa
-	if n.Sign() < 0 {
-		compact |= 0x00800000
-	}
-	return compact
+	return workmath.BigToCompact(n)
 }
 
 // CalcWork calculates a work value from difficulty bits.  Bitcoin increases
@@ -140,17 +65,7 @@ func BigToCompact(n *big.Int) uint32 {
 // potential division by zero and really small floating point numbers, the
 // result adds 1 to the denominator and multiplies the numerator by 2^256.
 func CalcWork(bits uint32) *big.Int {
-	// Return a work value of zero if the passed difficulty bits represent
-	// a negative number. Note this should not happen in practice with valid
-	// blocks, but an invalid block could trigger it.
-	difficultyNum := CompactToBig(bits)
-	if difficultyNum.Sign() <= 0 {
-		return big.NewInt(0)
-	}
-
-	// (1 << 256) / (difficultyNum + 1)
-	denominator := new(big.Int).Add(difficultyNum, bigOne)
-	return new(big.Int).Div(oneLsh256, denominator)
+	return workmath.CalcWork(bits)
 }
 
 // calcEasiestDifficulty calculates the easiest possible difficulty that a block
diff --git a/blockchain/fullblocktests/generate.go b/blockchain/fullblocktests/generate.go
index e8fad241fa..2b499c4e8c 100644
--- a/blockchain/fullblocktests/generate.go
+++ b/blockchain/fullblocktests/generate.go
@@ -14,11 +14,11 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
-	"math"
 	"runtime"
 	"time"
 
 	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/blockchain/internal/testhelper"
 	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
@@ -43,16 +43,6 @@ const (
 	numLargeReorgBlocks = 1088
 )
 
-var (
-	// opTrueScript is simply a public key script that contains the OP_TRUE
-	// opcode.  It is defined here to reduce garbage creation.
-	opTrueScript = []byte{txscript.OP_TRUE}
-
-	// lowFee is a single satoshi and exists to make the test code more
-	// readable.
-	lowFee = btcutil.Amount(1)
-)
-
 // TestInstance is an interface that describes a specific test instance returned
 // by the tests generated in this package.  It should be type asserted to one
 // of the concrete test instance types in order to test accordingly.
@@ -165,31 +155,6 @@ type BlockDisconnectExpectUTXO struct {
 // This implements the TestInstance interface.
 func (b BlockDisconnectExpectUTXO) FullBlockTestInstance() {}
 
-// spendableOut represents a transaction output that is spendable along with
-// additional metadata such as the block its in and how much it pays.
-type spendableOut struct {
-	prevOut wire.OutPoint
-	amount  btcutil.Amount
-}
-
-// makeSpendableOutForTx returns a spendable output for the given transaction
-// and transaction output index within the transaction.
-func makeSpendableOutForTx(tx *wire.MsgTx, txOutIndex uint32) spendableOut {
-	return spendableOut{
-		prevOut: wire.OutPoint{
-			Hash:  tx.TxHash(),
-			Index: txOutIndex,
-		},
-		amount: btcutil.Amount(tx.TxOut[txOutIndex].Value),
-	}
-}
-
-// makeSpendableOut returns a spendable output for the given block, transaction
-// index within the block, and transaction output index within the transaction.
-func makeSpendableOut(block *wire.MsgBlock, txIndex, txOutIndex uint32) spendableOut {
-	return makeSpendableOutForTx(block.Transactions[txIndex], txOutIndex)
-}
-
 // testGenerator houses state used to easy the process of generating test blocks
 // that build from one another along with housing other useful things such as
 // available spendable outputs used throughout the tests.
@@ -203,7 +168,7 @@ type testGenerator struct {
 	blockHeights map[string]int32
 
 	// Used for tracking spendable coinbase outputs.
-	spendableOuts     []spendableOut
+	spendableOuts     []testhelper.SpendableOut
 	prevCollectedHash chainhash.Hash
 
 	// Common key for any tests which require signed transactions.
@@ -255,62 +220,12 @@ func pushDataScript(items ...[]byte) []byte {
 	return script
 }
 
-// standardCoinbaseScript returns a standard script suitable for use as the
-// signature script of the coinbase transaction of a new block.  In particular,
-// it starts with the block height that is required by version 2 blocks.
-func standardCoinbaseScript(blockHeight int32, extraNonce uint64) ([]byte, error) {
-	return txscript.NewScriptBuilder().AddInt64(int64(blockHeight)).
-		AddInt64(int64(extraNonce)).Script()
-}
-
-// opReturnScript returns a provably-pruneable OP_RETURN script with the
-// provided data.
-func opReturnScript(data []byte) []byte {
-	builder := txscript.NewScriptBuilder()
-	script, err := builder.AddOp(txscript.OP_RETURN).AddData(data).Script()
-	if err != nil {
-		panic(err)
-	}
-	return script
-}
-
-// uniqueOpReturnScript returns a standard provably-pruneable OP_RETURN script
-// with a random uint64 encoded as the data.
-func uniqueOpReturnScript() []byte {
-	rand, err := wire.RandomUint64()
-	if err != nil {
-		panic(err)
-	}
-
-	data := make([]byte, 8)
-	binary.LittleEndian.PutUint64(data[0:8], rand)
-	return opReturnScript(data)
-}
-
 // createCoinbaseTx returns a coinbase transaction paying an appropriate
 // subsidy based on the passed block height.  The coinbase signature script
 // conforms to the requirements of version 2 blocks.
 func (g *testGenerator) createCoinbaseTx(blockHeight int32) *wire.MsgTx {
-	extraNonce := uint64(0)
-	coinbaseScript, err := standardCoinbaseScript(blockHeight, extraNonce)
-	if err != nil {
-		panic(err)
-	}
-
-	tx := wire.NewMsgTx(1)
-	tx.AddTxIn(&wire.TxIn{
-		// Coinbase transactions have no inputs, so previous outpoint is
-		// zero hash and max index.
-		PreviousOutPoint: *wire.NewOutPoint(&chainhash.Hash{},
-			wire.MaxPrevOutIndex),
-		Sequence:        wire.MaxTxInSequenceNum,
-		SignatureScript: coinbaseScript,
-	})
-	tx.AddTxOut(&wire.TxOut{
-		Value:    blockchain.CalcBlockSubsidy(blockHeight, g.params),
-		PkScript: opTrueScript,
-	})
-	return tx
+	return testhelper.CreateCoinbaseTx(
+		blockHeight, blockchain.CalcBlockSubsidy(blockHeight, g.params))
 }
 
 // calcMerkleRoot creates a merkle tree from the slice of transactions and
@@ -327,71 +242,6 @@ func calcMerkleRoot(txns []*wire.MsgTx) chainhash.Hash {
 	return blockchain.CalcMerkleRoot(utilTxns, false)
 }
 
-// solveBlock attempts to find a nonce which makes the passed block header hash
-// to a value less than the target difficulty.  When a successful solution is
-// found true is returned and the nonce field of the passed header is updated
-// with the solution.  False is returned if no solution exists.
-//
-// NOTE: This function will never solve blocks with a nonce of 0.  This is done
-// so the 'nextBlock' function can properly detect when a nonce was modified by
-// a munge function.
-func solveBlock(header *wire.BlockHeader) bool {
-	// sbResult is used by the solver goroutines to send results.
-	type sbResult struct {
-		found bool
-		nonce uint32
-	}
-
-	// solver accepts a block header and a nonce range to test. It is
-	// intended to be run as a goroutine.
-	targetDifficulty := blockchain.CompactToBig(header.Bits)
-	quit := make(chan bool)
-	results := make(chan sbResult)
-	solver := func(hdr wire.BlockHeader, startNonce, stopNonce uint32) {
-		// We need to modify the nonce field of the header, so make sure
-		// we work with a copy of the original header.
-		for i := startNonce; i >= startNonce && i <= stopNonce; i++ {
-			select {
-			case <-quit:
-				return
-			default:
-				hdr.Nonce = i
-				hash := hdr.BlockHash()
-				if blockchain.HashToBig(&hash).Cmp(
-					targetDifficulty) <= 0 {
-
-					results <- sbResult{true, i}
-					return
-				}
-			}
-		}
-		results <- sbResult{false, 0}
-	}
-
-	startNonce := uint32(1)
-	stopNonce := uint32(math.MaxUint32)
-	numCores := uint32(runtime.NumCPU())
-	noncesPerCore := (stopNonce - startNonce) / numCores
-	for i := uint32(0); i < numCores; i++ {
-		rangeStart := startNonce + (noncesPerCore * i)
-		rangeStop := startNonce + (noncesPerCore * (i + 1)) - 1
-		if i == numCores-1 {
-			rangeStop = stopNonce
-		}
-		go solver(*header, rangeStart, rangeStop)
-	}
-	for i := uint32(0); i < numCores; i++ {
-		result := <-results
-		if result.found {
-			close(quit)
-			header.Nonce = result.nonce
-			return true
-		}
-	}
-
-	return false
-}
-
 // additionalCoinbase returns a function that itself takes a block and
 // modifies it by adding the provided amount to coinbase subsidy.
 func additionalCoinbase(amount btcutil.Amount) func(*wire.MsgBlock) {
@@ -444,33 +294,14 @@ func additionalTx(tx *wire.MsgTx) func(*wire.MsgBlock) {
 	}
 }
 
-// createSpendTx creates a transaction that spends from the provided spendable
-// output and includes an additional unique OP_RETURN output to ensure the
-// transaction ends up with a unique hash.  The script is a simple OP_TRUE
-// script which avoids the need to track addresses and signature scripts in the
-// tests.
-func createSpendTx(spend *spendableOut, fee btcutil.Amount) *wire.MsgTx {
-	spendTx := wire.NewMsgTx(1)
-	spendTx.AddTxIn(&wire.TxIn{
-		PreviousOutPoint: spend.prevOut,
-		Sequence:         wire.MaxTxInSequenceNum,
-		SignatureScript:  nil,
-	})
-	spendTx.AddTxOut(wire.NewTxOut(int64(spend.amount-fee),
-		opTrueScript))
-	spendTx.AddTxOut(wire.NewTxOut(0, uniqueOpReturnScript()))
-
-	return spendTx
-}
-
 // createSpendTxForTx creates a transaction that spends from the first output of
 // the provided transaction and includes an additional unique OP_RETURN output
 // to ensure the transaction ends up with a unique hash.  The public key script
 // is a simple OP_TRUE script which avoids the need to track addresses and
 // signature scripts in the tests.  The signature script is nil.
 func createSpendTxForTx(tx *wire.MsgTx, fee btcutil.Amount) *wire.MsgTx {
-	spend := makeSpendableOutForTx(tx, 0)
-	return createSpendTx(&spend, fee)
+	spend := testhelper.MakeSpendableOutForTx(tx, 0)
+	return testhelper.CreateSpendTx(&spend, fee)
 }
 
 // nextBlock builds a new block that extends the current tip associated with the
@@ -492,7 +323,7 @@ func createSpendTxForTx(tx *wire.MsgTx, fee btcutil.Amount) *wire.MsgTx {
 // applied after all munge functions have been invoked:
 // - The merkle root will be recalculated unless it was manually changed
 // - The block will be solved unless the nonce was changed
-func (g *testGenerator) nextBlock(blockName string, spend *spendableOut, mungers ...func(*wire.MsgBlock)) *wire.MsgBlock {
+func (g *testGenerator) nextBlock(blockName string, spend *testhelper.SpendableOut, mungers ...func(*wire.MsgBlock)) *wire.MsgBlock {
 	// Create coinbase transaction for the block using any additional
 	// subsidy if specified.
 	nextHeight := g.tipHeight + 1
@@ -510,7 +341,7 @@ func (g *testGenerator) nextBlock(blockName string, spend *spendableOut, mungers
 		// add it to the list of transactions to include in the block.
 		// The script is a simple OP_TRUE script in order to avoid the
 		// need to track addresses and signature scripts in the tests.
-		txns = append(txns, createSpendTx(spend, fee))
+		txns = append(txns, testhelper.CreateSpendTx(spend, fee))
 	}
 
 	// Use a timestamp that is one second after the previous block unless
@@ -547,7 +378,7 @@ func (g *testGenerator) nextBlock(blockName string, spend *spendableOut, mungers
 
 	// Only solve the block if the nonce wasn't manually changed by a munge
 	// function.
-	if block.Header.Nonce == curNonce && !solveBlock(&block.Header) {
+	if block.Header.Nonce == curNonce && !testhelper.SolveBlock(&block.Header) {
 		panic(fmt.Sprintf("Unable to solve block at height %d",
 			nextHeight))
 	}
@@ -594,7 +425,7 @@ func (g *testGenerator) setTip(blockName string) {
 
 // oldestCoinbaseOuts removes the oldest coinbase output that was previously
 // saved to the generator and returns the set as a slice.
-func (g *testGenerator) oldestCoinbaseOut() spendableOut {
+func (g *testGenerator) oldestCoinbaseOut() testhelper.SpendableOut {
 	op := g.spendableOuts[0]
 	g.spendableOuts = g.spendableOuts[1:]
 	return op
@@ -603,7 +434,7 @@ func (g *testGenerator) oldestCoinbaseOut() spendableOut {
 // saveTipCoinbaseOut adds the coinbase tx output in the current tip block to
 // the list of spendable outputs.
 func (g *testGenerator) saveTipCoinbaseOut() {
-	g.spendableOuts = append(g.spendableOuts, makeSpendableOut(g.tip, 0, 0))
+	g.spendableOuts = append(g.spendableOuts, testhelper.MakeSpendableOut(g.tip, 0, 0))
 	g.prevCollectedHash = g.tip.BlockHash()
 }
 
@@ -947,7 +778,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	tests = append(tests, testInstances)
 
 	// Collect spendable outputs.  This simplifies the code below.
-	var outs []*spendableOut
+	var outs []*testhelper.SpendableOut
 	for i := uint16(0); i < coinbaseMaturity; i++ {
 		op := g.oldestCoinbaseOut()
 		outs = append(outs, &op)
@@ -985,7 +816,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//               \-> b3(1)
 	g.setTip("b1")
 	g.nextBlock("b3", outs[1])
-	b3Tx1Out := makeSpendableOut(g.tip, 1, 0)
+	b3Tx1Out := testhelper.MakeSpendableOut(g.tip, 1, 0)
 	acceptedToSideChainWithExpectedTip("b2")
 
 	// Extend b3 fork to make the alternative chain longer and force reorg.
@@ -1298,9 +1129,9 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//                 \-> b38(b37.tx[1])
 	//
 	g.setTip("b35")
-	doubleSpendTx := createSpendTx(outs[11], lowFee)
+	doubleSpendTx := testhelper.CreateSpendTx(outs[11], testhelper.LowFee)
 	g.nextBlock("b37", outs[11], additionalTx(doubleSpendTx))
-	b37Tx1Out := makeSpendableOut(g.tip, 1, 0)
+	b37Tx1Out := testhelper.MakeSpendableOut(g.tip, 1, 0)
 	rejected(blockchain.ErrMissingTxOut)
 
 	g.setTip("b35")
@@ -1336,7 +1167,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		txnsNeeded := (maxBlockSigOps / redeemScriptSigOps) + 1
 		prevTx := b.Transactions[1]
 		for i := 0; i < txnsNeeded; i++ {
-			prevTx = createSpendTxForTx(prevTx, lowFee)
+			prevTx = createSpendTxForTx(prevTx, testhelper.LowFee)
 			prevTx.TxOut[0].Value -= 2
 			prevTx.AddTxOut(wire.NewTxOut(2, p2shScript))
 			b.AddTransaction(prevTx)
@@ -1356,8 +1187,8 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		for i := 0; i < txnsNeeded; i++ {
 			// Create a signed transaction that spends from the
 			// associated p2sh output in b39.
-			spend := makeSpendableOutForTx(b39.Transactions[i+2], 2)
-			tx := createSpendTx(&spend, lowFee)
+			spend := testhelper.MakeSpendableOutForTx(b39.Transactions[i+2], 2)
+			tx := testhelper.CreateSpendTx(&spend, testhelper.LowFee)
 			sig, err := txscript.RawTxInSignature(tx, 0,
 				redeemScript, txscript.SigHashAll, g.privKey)
 			if err != nil {
@@ -1373,7 +1204,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		// the block one over the max allowed.
 		fill := maxBlockSigOps - (txnsNeeded * redeemScriptSigOps) + 1
 		finalTx := b.Transactions[len(b.Transactions)-1]
-		tx := createSpendTxForTx(finalTx, lowFee)
+		tx := createSpendTxForTx(finalTx, testhelper.LowFee)
 		tx.TxOut[0].PkScript = repeatOpcode(txscript.OP_CHECKSIG, fill)
 		b.AddTransaction(tx)
 	})
@@ -1387,8 +1218,8 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	g.nextBlock("b41", outs[12], func(b *wire.MsgBlock) {
 		txnsNeeded := (maxBlockSigOps / redeemScriptSigOps)
 		for i := 0; i < txnsNeeded; i++ {
-			spend := makeSpendableOutForTx(b39.Transactions[i+2], 2)
-			tx := createSpendTx(&spend, lowFee)
+			spend := testhelper.MakeSpendableOutForTx(b39.Transactions[i+2], 2)
+			tx := testhelper.CreateSpendTx(&spend, testhelper.LowFee)
 			sig, err := txscript.RawTxInSignature(tx, 0,
 				redeemScript, txscript.SigHashAll, g.privKey)
 			if err != nil {
@@ -1407,7 +1238,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 			return
 		}
 		finalTx := b.Transactions[len(b.Transactions)-1]
-		tx := createSpendTxForTx(finalTx, lowFee)
+		tx := createSpendTxForTx(finalTx, testhelper.LowFee)
 		tx.TxOut[0].PkScript = repeatOpcode(txscript.OP_CHECKSIG, fill)
 		b.AddTransaction(tx)
 	})
@@ -1437,7 +1268,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//   ... -> b43(13)
 	//                 \-> b44(14)
 	g.nextBlock("b44", nil, func(b *wire.MsgBlock) {
-		nonCoinbaseTx := createSpendTx(outs[14], lowFee)
+		nonCoinbaseTx := testhelper.CreateSpendTx(outs[14], testhelper.LowFee)
 		b.Transactions[0] = nonCoinbaseTx
 	})
 	rejected(blockchain.ErrFirstTxNotCoinbase)
@@ -1642,7 +1473,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	g.setTip("b55")
 	b57 := g.nextBlock("b57", outs[16], func(b *wire.MsgBlock) {
 		tx2 := b.Transactions[1]
-		tx3 := createSpendTxForTx(tx2, lowFee)
+		tx3 := createSpendTxForTx(tx2, testhelper.LowFee)
 		b.AddTransaction(tx3)
 	})
 	g.assertTipBlockNumTxns(3)
@@ -1687,7 +1518,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		// in the block.
 		spendTx := b.Transactions[1]
 		for i := 0; i < 4; i++ {
-			spendTx = createSpendTxForTx(spendTx, lowFee)
+			spendTx = createSpendTxForTx(spendTx, testhelper.LowFee)
 			b.AddTransaction(spendTx)
 		}
 
@@ -1719,7 +1550,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//                 \-> b59(17)
 	g.setTip("b57")
 	g.nextBlock("b59", outs[17], func(b *wire.MsgBlock) {
-		b.Transactions[1].TxOut[0].Value = int64(outs[17].amount) + 1
+		b.Transactions[1].TxOut[0].Value = int64(outs[17].Amount) + 1
 	})
 	rejected(blockchain.ErrSpendTooHigh)
 
@@ -1824,7 +1655,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//   ... b64(18) -> b65(19)
 	g.setTip("b64")
 	g.nextBlock("b65", outs[19], func(b *wire.MsgBlock) {
-		tx3 := createSpendTxForTx(b.Transactions[1], lowFee)
+		tx3 := createSpendTxForTx(b.Transactions[1], testhelper.LowFee)
 		b.AddTransaction(tx3)
 	})
 	accepted()
@@ -1834,8 +1665,8 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	//   ... -> b65(19)
 	//                 \-> b66(20)
 	g.nextBlock("b66", nil, func(b *wire.MsgBlock) {
-		tx2 := createSpendTx(outs[20], lowFee)
-		tx3 := createSpendTxForTx(tx2, lowFee)
+		tx2 := testhelper.CreateSpendTx(outs[20], testhelper.LowFee)
+		tx3 := createSpendTxForTx(tx2, testhelper.LowFee)
 		b.AddTransaction(tx3)
 		b.AddTransaction(tx2)
 	})
@@ -1849,8 +1680,8 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	g.setTip("b65")
 	g.nextBlock("b67", outs[20], func(b *wire.MsgBlock) {
 		tx2 := b.Transactions[1]
-		tx3 := createSpendTxForTx(tx2, lowFee)
-		tx4 := createSpendTxForTx(tx2, lowFee)
+		tx3 := createSpendTxForTx(tx2, testhelper.LowFee)
+		tx4 := createSpendTxForTx(tx2, testhelper.LowFee)
 		b.AddTransaction(tx3)
 		b.AddTransaction(tx4)
 	})
@@ -1973,7 +1804,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		txscript.OP_ELSE, txscript.OP_TRUE, txscript.OP_ENDIF}
 	g.nextBlock("b74", outs[23], replaceSpendScript(script), func(b *wire.MsgBlock) {
 		tx2 := b.Transactions[1]
-		tx3 := createSpendTxForTx(tx2, lowFee)
+		tx3 := createSpendTxForTx(tx2, testhelper.LowFee)
 		tx3.TxIn[0].SignatureScript = []byte{txscript.OP_FALSE}
 		b.AddTransaction(tx3)
 	})
@@ -1994,7 +1825,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		const zeroCoin = int64(0)
 		spendTx := b.Transactions[1]
 		for i := 0; i < numAdditionalOutputs; i++ {
-			spendTx.AddTxOut(wire.NewTxOut(zeroCoin, opTrueScript))
+			spendTx.AddTxOut(wire.NewTxOut(zeroCoin, testhelper.OpTrueScript))
 		}
 
 		// Add transactions spending from the outputs added above that
@@ -2003,14 +1834,14 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		// NOTE: The createSpendTx func adds the OP_RETURN output.
 		zeroFee := btcutil.Amount(0)
 		for i := uint32(0); i < numAdditionalOutputs; i++ {
-			spend := makeSpendableOut(b, 1, i+2)
-			tx := createSpendTx(&spend, zeroFee)
+			spend := testhelper.MakeSpendableOut(b, 1, i+2)
+			tx := testhelper.CreateSpendTx(&spend, zeroFee)
 			b.AddTransaction(tx)
 		}
 	})
 	g.assertTipBlockNumTxns(6)
 	g.assertTipBlockTxOutOpReturn(5, 1)
-	b75OpReturnOut := makeSpendableOut(g.tip, 5, 1)
+	b75OpReturnOut := testhelper.MakeSpendableOut(g.tip, 5, 1)
 	accepted()
 
 	// Reorg to a side chain that does not contain the OP_RETURNs.
@@ -2043,7 +1874,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	// An OP_RETURN output doesn't have any value and the default behavior
 	// of nextBlock is to assign a fee of one, so increment the amount here
 	// to effective negate that behavior.
-	b75OpReturnOut.amount++
+	b75OpReturnOut.Amount++
 	g.nextBlock("b80", &b75OpReturnOut)
 	rejected(blockchain.ErrMissingTxOut)
 
@@ -2059,7 +1890,10 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 		const zeroCoin = int64(0)
 		spendTx := b.Transactions[1]
 		for i := 0; i < numAdditionalOutputs; i++ {
-			opRetScript := uniqueOpReturnScript()
+			opRetScript, err := testhelper.UniqueOpReturnScript()
+			if err != nil {
+				panic(err)
+			}
 			spendTx.AddTxOut(wire.NewTxOut(zeroCoin, opRetScript))
 		}
 	})
@@ -2075,7 +1909,7 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	g.nextBlock("b82a", outs[28])
 	accepted()
 
-	b82aTx1Out0 := makeSpendableOut(g.tip, 1, 0)
+	b82aTx1Out0 := testhelper.MakeSpendableOut(g.tip, 1, 0)
 	g.nextBlock("b83a", &b82aTx1Out0)
 	accepted()
 
@@ -2097,17 +1931,17 @@ func Generate(includeLargeReorg bool) (tests [][]TestInstance, err error) {
 	// We expect b82a output to now be a utxo since b83a was spending it and it was
 	// removed from the main chain.
 	blockDisconnectExpectUTXO("b82aTx1Out0",
-		true, b82aTx1Out0.prevOut, g.blocksByName["b83a"].BlockHash())
+		true, b82aTx1Out0.PrevOut, g.blocksByName["b83a"].BlockHash())
 
 	// We expect the output from b82 to not exist once b82a itself has been removed
 	// from the main chain.
 	blockDisconnectExpectUTXO("b82aTx1Out0",
-		false, b82aTx1Out0.prevOut, g.blocksByName["b82a"].BlockHash())
+		false, b82aTx1Out0.PrevOut, g.blocksByName["b82a"].BlockHash())
 
 	// The output that was being spent in b82a should exist after the removal of
 	// b82a.
 	blockDisconnectExpectUTXO("outs[28]",
-		true, outs[28].prevOut, g.blocksByName["b82a"].BlockHash())
+		true, outs[28].PrevOut, g.blocksByName["b82a"].BlockHash())
 
 	// Create block 84 and reorg out the sidechain with b83a as the tip.
 	//
diff --git a/blockchain/internal/testhelper/README.md b/blockchain/internal/testhelper/README.md
new file mode 100644
index 0000000000..40b339bf79
--- /dev/null
+++ b/blockchain/internal/testhelper/README.md
@@ -0,0 +1,16 @@
+testhelper
+==========
+
+[![Build Status](https://github.com/btcsuite/btcd/workflows/Build%20and%20Test/badge.svg)](https://github.com/btcsuite/btcd/actions)
+[![ISC License](http://img.shields.io/badge/license-ISC-blue.svg)](http://copyfree.org)
+[![GoDoc](https://img.shields.io/badge/godoc-reference-blue.svg)](https://pkg.go.dev/github.com/btcsuite/btcd/blockchain/testhelper)
+
+Package testhelper provides functions that are used internally in the
+btcd/blockchain and btcd/blockchain/fullblocktests package to test consensus
+validation rules.  Mainly provided to avoid dependency cycles internally among
+the different packages in btcd.
+
+## License
+
+Package testhelper is licensed under the [copyfree](http://copyfree.org) ISC
+License.
diff --git a/blockchain/internal/testhelper/common.go b/blockchain/internal/testhelper/common.go
new file mode 100644
index 0000000000..681097480c
--- /dev/null
+++ b/blockchain/internal/testhelper/common.go
@@ -0,0 +1,194 @@
+package testhelper
+
+import (
+	"encoding/binary"
+	"math"
+	"runtime"
+
+	"github.com/btcsuite/btcd/blockchain/internal/workmath"
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+)
+
+var (
+	// OpTrueScript is simply a public key script that contains the OP_TRUE
+	// opcode.  It is defined here to reduce garbage creation.
+	OpTrueScript = []byte{txscript.OP_TRUE}
+
+	// LowFee is a single satoshi and exists to make the test code more
+	// readable.
+	LowFee = btcutil.Amount(1)
+)
+
+// CreateSpendTx creates a transaction that spends from the provided spendable
+// output and includes an additional unique OP_RETURN output to ensure the
+// transaction ends up with a unique hash.  The script is a simple OP_TRUE
+// script which avoids the need to track addresses and signature scripts in the
+// tests.
+func CreateSpendTx(spend *SpendableOut, fee btcutil.Amount) *wire.MsgTx {
+	spendTx := wire.NewMsgTx(1)
+	spendTx.AddTxIn(&wire.TxIn{
+		PreviousOutPoint: spend.PrevOut,
+		Sequence:         wire.MaxTxInSequenceNum,
+		SignatureScript:  nil,
+	})
+	spendTx.AddTxOut(wire.NewTxOut(int64(spend.Amount-fee),
+		OpTrueScript))
+	opRetScript, err := UniqueOpReturnScript()
+	if err != nil {
+		panic(err)
+	}
+	spendTx.AddTxOut(wire.NewTxOut(0, opRetScript))
+
+	return spendTx
+}
+
+// CreateCoinbaseTx returns a coinbase transaction paying an appropriate
+// subsidy based on the passed block height and the block subsidy.  The
+// coinbase signature script conforms to the requirements of version 2 blocks.
+func CreateCoinbaseTx(blockHeight int32, blockSubsidy int64) *wire.MsgTx {
+	extraNonce := uint64(0)
+	coinbaseScript, err := StandardCoinbaseScript(blockHeight, extraNonce)
+	if err != nil {
+		panic(err)
+	}
+
+	tx := wire.NewMsgTx(1)
+	tx.AddTxIn(&wire.TxIn{
+		// Coinbase transactions have no inputs, so previous outpoint is
+		// zero hash and max index.
+		PreviousOutPoint: *wire.NewOutPoint(&chainhash.Hash{},
+			wire.MaxPrevOutIndex),
+		Sequence:        wire.MaxTxInSequenceNum,
+		SignatureScript: coinbaseScript,
+	})
+	tx.AddTxOut(&wire.TxOut{
+		Value:    blockSubsidy,
+		PkScript: OpTrueScript,
+	})
+	return tx
+}
+
+// StandardCoinbaseScript returns a standard script suitable for use as the
+// signature script of the coinbase transaction of a new block.  In particular,
+// it starts with the block height that is required by version 2 blocks.
+func StandardCoinbaseScript(blockHeight int32, extraNonce uint64) ([]byte, error) {
+	return txscript.NewScriptBuilder().AddInt64(int64(blockHeight)).
+		AddInt64(int64(extraNonce)).Script()
+}
+
+// OpReturnScript returns a provably-pruneable OP_RETURN script with the
+// provided data.
+func OpReturnScript(data []byte) ([]byte, error) {
+	builder := txscript.NewScriptBuilder()
+	script, err := builder.AddOp(txscript.OP_RETURN).AddData(data).Script()
+	if err != nil {
+		return nil, err
+	}
+	return script, nil
+}
+
+// UniqueOpReturnScript returns a standard provably-pruneable OP_RETURN script
+// with a random uint64 encoded as the data.
+func UniqueOpReturnScript() ([]byte, error) {
+	rand, err := wire.RandomUint64()
+	if err != nil {
+		return nil, err
+	}
+
+	data := make([]byte, 8)
+	binary.LittleEndian.PutUint64(data[0:8], rand)
+	return OpReturnScript(data)
+}
+
+// SpendableOut represents a transaction output that is spendable along with
+// additional metadata such as the block its in and how much it pays.
+type SpendableOut struct {
+	PrevOut wire.OutPoint
+	Amount  btcutil.Amount
+}
+
+// MakeSpendableOutForTx returns a spendable output for the given transaction
+// and transaction output index within the transaction.
+func MakeSpendableOutForTx(tx *wire.MsgTx, txOutIndex uint32) SpendableOut {
+	return SpendableOut{
+		PrevOut: wire.OutPoint{
+			Hash:  tx.TxHash(),
+			Index: txOutIndex,
+		},
+		Amount: btcutil.Amount(tx.TxOut[txOutIndex].Value),
+	}
+}
+
+// MakeSpendableOut returns a spendable output for the given block, transaction
+// index within the block, and transaction output index within the transaction.
+func MakeSpendableOut(block *wire.MsgBlock, txIndex, txOutIndex uint32) SpendableOut {
+	return MakeSpendableOutForTx(block.Transactions[txIndex], txOutIndex)
+}
+
+// SolveBlock attempts to find a nonce which makes the passed block header hash
+// to a value less than the target difficulty.  When a successful solution is
+// found true is returned and the nonce field of the passed header is updated
+// with the solution.  False is returned if no solution exists.
+//
+// NOTE: This function will never solve blocks with a nonce of 0.  This is done
+// so the 'nextBlock' function can properly detect when a nonce was modified by
+// a munge function.
+func SolveBlock(header *wire.BlockHeader) bool {
+	// sbResult is used by the solver goroutines to send results.
+	type sbResult struct {
+		found bool
+		nonce uint32
+	}
+
+	// solver accepts a block header and a nonce range to test. It is
+	// intended to be run as a goroutine.
+	targetDifficulty := workmath.CompactToBig(header.Bits)
+	quit := make(chan bool)
+	results := make(chan sbResult)
+	solver := func(hdr wire.BlockHeader, startNonce, stopNonce uint32) {
+		// We need to modify the nonce field of the header, so make sure
+		// we work with a copy of the original header.
+		for i := startNonce; i >= startNonce && i <= stopNonce; i++ {
+			select {
+			case <-quit:
+				return
+			default:
+				hdr.Nonce = i
+				hash := hdr.BlockHash()
+				if workmath.HashToBig(&hash).Cmp(
+					targetDifficulty) <= 0 {
+
+					results <- sbResult{true, i}
+					return
+				}
+			}
+		}
+		results <- sbResult{false, 0}
+	}
+
+	startNonce := uint32(1)
+	stopNonce := uint32(math.MaxUint32)
+	numCores := uint32(runtime.NumCPU())
+	noncesPerCore := (stopNonce - startNonce) / numCores
+	for i := uint32(0); i < numCores; i++ {
+		rangeStart := startNonce + (noncesPerCore * i)
+		rangeStop := startNonce + (noncesPerCore * (i + 1)) - 1
+		if i == numCores-1 {
+			rangeStop = stopNonce
+		}
+		go solver(*header, rangeStart, rangeStop)
+	}
+	for i := uint32(0); i < numCores; i++ {
+		result := <-results
+		if result.found {
+			close(quit)
+			header.Nonce = result.nonce
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/blockchain/internal/workmath/README.md b/blockchain/internal/workmath/README.md
new file mode 100644
index 0000000000..879b2dcfd7
--- /dev/null
+++ b/blockchain/internal/workmath/README.md
@@ -0,0 +1,15 @@
+workmath
+==========
+
+[![Build Status](https://github.com/btcsuite/btcd/workflows/Build%20and%20Test/badge.svg)](https://github.com/btcsuite/btcd/actions)
+[![ISC License](http://img.shields.io/badge/license-ISC-blue.svg)](http://copyfree.org)
+[![GoDoc](https://img.shields.io/badge/godoc-reference-blue.svg)](https://pkg.go.dev/github.com/btcsuite/btcd/workmath)
+
+Package workmath provides utility functions that are related with calculating
+the work from difficulty bits.  This package was introduced to avoid import
+cycles in btcd.
+
+## License
+
+Package workmath is licensed under the [copyfree](http://copyfree.org) ISC
+License.
diff --git a/blockchain/internal/workmath/difficulty.go b/blockchain/internal/workmath/difficulty.go
new file mode 100644
index 0000000000..8ff7adad1c
--- /dev/null
+++ b/blockchain/internal/workmath/difficulty.go
@@ -0,0 +1,153 @@
+// Copyright (c) 2013-2017 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package workmath
+
+import (
+	"math/big"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+)
+
+var (
+	// bigOne is 1 represented as a big.Int.  It is defined here to avoid
+	// the overhead of creating it multiple times.
+	bigOne = big.NewInt(1)
+
+	// oneLsh256 is 1 shifted left 256 bits.  It is defined here to avoid
+	// the overhead of creating it multiple times.
+	oneLsh256 = new(big.Int).Lsh(bigOne, 256)
+)
+
+// HashToBig converts a chainhash.Hash into a big.Int that can be used to
+// perform math comparisons.
+func HashToBig(hash *chainhash.Hash) *big.Int {
+	// A Hash is in little-endian, but the big package wants the bytes in
+	// big-endian, so reverse them.
+	buf := *hash
+	blen := len(buf)
+	for i := 0; i < blen/2; i++ {
+		buf[i], buf[blen-1-i] = buf[blen-1-i], buf[i]
+	}
+
+	return new(big.Int).SetBytes(buf[:])
+}
+
+// CompactToBig converts a compact representation of a whole number N to an
+// unsigned 32-bit number.  The representation is similar to IEEE754 floating
+// point numbers.
+//
+// Like IEEE754 floating point, there are three basic components: the sign,
+// the exponent, and the mantissa.  They are broken out as follows:
+//
+// - the most significant 8 bits represent the unsigned base 256 exponent
+// - bit 23 (the 24th bit) represents the sign bit
+// - the least significant 23 bits represent the mantissa
+//
+//	-------------------------------------------------
+//	|   Exponent     |    Sign    |    Mantissa     |
+//	-------------------------------------------------
+//	| 8 bits [31-24] | 1 bit [23] | 23 bits [22-00] |
+//	-------------------------------------------------
+//
+// The formula to calculate N is:
+//
+//	N = (-1^sign) * mantissa * 256^(exponent-3)
+//
+// This compact form is only used in bitcoin to encode unsigned 256-bit numbers
+// which represent difficulty targets, thus there really is not a need for a
+// sign bit, but it is implemented here to stay consistent with bitcoind.
+func CompactToBig(compact uint32) *big.Int {
+	// Extract the mantissa, sign bit, and exponent.
+	mantissa := compact & 0x007fffff
+	isNegative := compact&0x00800000 != 0
+	exponent := uint(compact >> 24)
+
+	// Since the base for the exponent is 256, the exponent can be treated
+	// as the number of bytes to represent the full 256-bit number.  So,
+	// treat the exponent as the number of bytes and shift the mantissa
+	// right or left accordingly.  This is equivalent to:
+	// N = mantissa * 256^(exponent-3)
+	var bn *big.Int
+	if exponent <= 3 {
+		mantissa >>= 8 * (3 - exponent)
+		bn = big.NewInt(int64(mantissa))
+	} else {
+		bn = big.NewInt(int64(mantissa))
+		bn.Lsh(bn, 8*(exponent-3))
+	}
+
+	// Make it negative if the sign bit is set.
+	if isNegative {
+		bn = bn.Neg(bn)
+	}
+
+	return bn
+}
+
+// BigToCompact converts a whole number N to a compact representation using
+// an unsigned 32-bit number.  The compact representation only provides 23 bits
+// of precision, so values larger than (2^23 - 1) only encode the most
+// significant digits of the number.  See CompactToBig for details.
+func BigToCompact(n *big.Int) uint32 {
+	// No need to do any work if it's zero.
+	if n.Sign() == 0 {
+		return 0
+	}
+
+	// Since the base for the exponent is 256, the exponent can be treated
+	// as the number of bytes.  So, shift the number right or left
+	// accordingly.  This is equivalent to:
+	// mantissa = mantissa / 256^(exponent-3)
+	var mantissa uint32
+	exponent := uint(len(n.Bytes()))
+	if exponent <= 3 {
+		mantissa = uint32(n.Bits()[0])
+		mantissa <<= 8 * (3 - exponent)
+	} else {
+		// Use a copy to avoid modifying the caller's original number.
+		tn := new(big.Int).Set(n)
+		mantissa = uint32(tn.Rsh(tn, 8*(exponent-3)).Bits()[0])
+	}
+
+	// When the mantissa already has the sign bit set, the number is too
+	// large to fit into the available 23-bits, so divide the number by 256
+	// and increment the exponent accordingly.
+	if mantissa&0x00800000 != 0 {
+		mantissa >>= 8
+		exponent++
+	}
+
+	// Pack the exponent, sign bit, and mantissa into an unsigned 32-bit
+	// int and return it.
+	compact := uint32(exponent<<24) | mantissa
+	if n.Sign() < 0 {
+		compact |= 0x00800000
+	}
+	return compact
+}
+
+// CalcWork calculates a work value from difficulty bits.  Bitcoin increases
+// the difficulty for generating a block by decreasing the value which the
+// generated hash must be less than.  This difficulty target is stored in each
+// block header using a compact representation as described in the documentation
+// for CompactToBig.  The main chain is selected by choosing the chain that has
+// the most proof of work (highest difficulty).  Since a lower target difficulty
+// value equates to higher actual difficulty, the work value which will be
+// accumulated must be the inverse of the difficulty.  Also, in order to avoid
+// potential division by zero and really small floating point numbers, the
+// result adds 1 to the denominator and multiplies the numerator by 2^256.
+func CalcWork(bits uint32) *big.Int {
+	// Return a work value of zero if the passed difficulty bits represent
+	// a negative number. Note this should not happen in practice with valid
+	// blocks, but an invalid block could trigger it.
+	difficultyNum := CompactToBig(bits)
+	if difficultyNum.Sign() <= 0 {
+		return big.NewInt(0)
+	}
+
+	// (1 << 256) / (difficultyNum + 1)
+	denominator := new(big.Int).Add(difficultyNum, bigOne)
+	return new(big.Int).Div(oneLsh256, denominator)
+}
diff --git a/blockchain/difficulty_test.go b/blockchain/internal/workmath/difficulty_test.go
similarity index 98%
rename from blockchain/difficulty_test.go
rename to blockchain/internal/workmath/difficulty_test.go
index c4d8fb6ef5..bed4d1f13f 100644
--- a/blockchain/difficulty_test.go
+++ b/blockchain/internal/workmath/difficulty_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
-package blockchain
+package workmath
 
 import (
 	"math/big"