/* calcDiff returns a bool given two block headers.  This bool is
true if the correct dificulty adjustment is seen in the "next" header.
Only feed it headers n-2016 and n-1, otherwise it will calculate a difficulty
when no adjustment should take place, and return false.
Note that the epoch is actually 2015 blocks long, which is confusing. */
func calcDiffAdjust(start, end wire.BlockHeader, p *chaincfg.Params) uint32 {
	duration := end.Timestamp.UnixNano() - start.Timestamp.UnixNano()
	if duration < minRetargetTimespan {
		log.Printf("whoa there, block %s off-scale high 4X diff adjustment!",
			end.BlockSha().String())
		duration = minRetargetTimespan
	} else if duration > maxRetargetTimespan {
		log.Printf("Uh-oh! block %s off-scale low 0.25X diff adjustment!\n",
			end.BlockSha().String())
		duration = maxRetargetTimespan
	}

	// calculation of new 32-byte difficulty target
	// first turn the previous target into a big int
	prevTarget := blockchain.CompactToBig(start.Bits)
	// new target is old * duration...
	newTarget := new(big.Int).Mul(prevTarget, big.NewInt(duration))
	// divided by 2 weeks
	newTarget.Div(newTarget, big.NewInt(int64(targetTimespan)))

	// clip again if above minimum target (too easy)
	if newTarget.Cmp(p.PowLimit) > 0 {
		newTarget.Set(p.PowLimit)
	}

	// calculate and return 4-byte 'bits' difficulty from 32-byte target
	return blockchain.BigToCompact(newTarget)
}

// This example demonstrates how to convert the compact "bits" in a block header
// which represent the target difficulty to a big integer and display it using
// the typical hex notation.
func ExampleCompactToBig() {
	// Convert the bits from block 300000 in the main block chain.
	bits := uint32(419465580)
	targetDifficulty := blockchain.CompactToBig(bits)

	// Display it in hex.
	fmt.Printf("%064x\n", targetDifficulty.Bytes())

	// Output:
	// 0000000000000000896c00000000000000000000000000000000000000000000
}

func TestCompactToBig(t *testing.T) {
	tests := []struct {
		in  uint32
		out int64
	}{
		{10000000, 0},
	}

	for x, test := range tests {
		n := blockchain.CompactToBig(test.in)
		want := big.NewInt(test.out)
		if n.Cmp(want) != 0 {
			t.Errorf("TestCompactToBig test #%d failed: got %d want %d\n",
				x, n.Int64(), want.Int64())
			return
		}
	}
}

/* checkProofOfWork verifies the header hashes into something
lower than specified by the 4-byte bits field. */
func checkProofOfWork(header wire.BlockHeader, p *chaincfg.Params) bool {
	target := blockchain.CompactToBig(header.Bits)

	// The target must more than 0.  Why can you even encode negative...
	if target.Sign() <= 0 {
		log.Printf("block target %064x is neagtive(??)\n", target.Bytes())
		return false
	}
	// The target must be less than the maximum allowed (difficulty 1)
	if target.Cmp(p.PowLimit) > 0 {
		log.Printf("block target %064x is "+
			"higher than max of %064x", target, p.PowLimit.Bytes())
		return false
	}
	// The header hash must be less than the claimed target in the header.
	blockHash := header.BlockSha()
	hashNum := blockchain.ShaHashToBig(&blockHash)
	if hashNum.Cmp(target) > 0 {
		log.Printf("block hash %064x is higher than "+
			"required target of %064x", hashNum, target)
		return false
	}
	return true
}

// solveBlock attempts to find some combination of a nonce, extra nonce, and
// current timestamp which makes the passed block hash to a value less than the
// target difficulty.  The timestamp is updated periodically and the passed
// block is modified with all tweaks during this process.  This means that
// when the function returns true, the block is ready for submission.
//
// This function will return early with false when conditions that trigger a
// stale block such as a new block showing up or periodically when there are
// new transactions and enough time has elapsed without finding a solution.
func (m *CPUMiner) solveBlock(msgBlock *wire.MsgBlock, blockHeight int32,
	ticker *time.Ticker, quit chan struct{}) bool {

	// Choose a random extra nonce offset for this block template and
	// worker.
	enOffset, err := wire.RandomUint64()
	if err != nil {
		minrLog.Errorf("Unexpected error while generating random "+
			"extra nonce offset: %v", err)
		enOffset = 0
	}

	// Create a couple of convenience variables.
	header := &msgBlock.Header
	targetDifficulty := blockchain.CompactToBig(header.Bits)

	// Initial state.
	lastGenerated := time.Now()
	lastTxUpdate := m.txSource.LastUpdated()
	hashesCompleted := uint64(0)

	// Note that the entire extra nonce range is iterated and the offset is
	// added relying on the fact that overflow will wrap around 0 as
	// provided by the Go spec.
	for extraNonce := uint64(0); extraNonce < maxExtraNonce; extraNonce++ {
		// Update the extra nonce in the block template with the
		// new value by regenerating the coinbase script and
		// setting the merkle root to the new value.  The
		UpdateExtraNonce(msgBlock, blockHeight, extraNonce+enOffset)

		// Search through the entire nonce range for a solution while
		// periodically checking for early quit and stale block
		// conditions along with updates to the speed monitor.
		for i := uint32(0); i <= maxNonce; i++ {
			select {
			case <-quit:
				return false

			case <-ticker.C:
				m.updateHashes <- hashesCompleted
				hashesCompleted = 0

				// The current block is stale if the best block
				// has changed.
				bestHash, _ := m.server.blockManager.chainState.Best()
				if !header.PrevBlock.IsEqual(bestHash) {
					return false
				}

				// The current block is stale if the memory pool
				// has been updated since the block template was
				// generated and it has been at least one
				// minute.
				if lastTxUpdate != m.txSource.LastUpdated() &&
					time.Now().After(lastGenerated.Add(time.Minute)) {

					return false
				}

				UpdateBlockTime(msgBlock, m.server.blockManager)

			default:
				// Non-blocking select to fall through
			}

			// Update the nonce and hash the block header.  Each
			// hash is actually a double sha256 (two hashes), so
			// increment the number of hashes completed for each
			// attempt accordingly.
			header.Nonce = i
			hash := header.BlockSha()
			hashesCompleted += 2

			// The block is solved when the new block hash is less
			// than the target difficulty.  Yay!
			if blockchain.ShaHashToBig(&hash).Cmp(targetDifficulty) <= 0 {
				m.updateHashes <- hashesCompleted
				return true
			}
		}
	}

	return false
}

//.........这里部分代码省略.........
			minrLog.Tracef("Skipping tx %s due to error in "+
				"ValidateTransactionScripts: %v", tx.Sha(), err)
			logSkippedDeps(tx, deps)
			continue
		}

		// Spend the transaction inputs in the block transaction store
		// and add an entry for it to ensure any transactions which
		// reference this one have it available as an input and can
		// ensure they aren't double spending.
		spendTransaction(blockTxStore, tx, nextBlockHeight)

		// Add the transaction to the block, increment counters, and
		// save the fees and signature operation counts to the block
		// template.
		blockTxns = append(blockTxns, tx)
		blockSize += txSize
		blockSigOps += numSigOps
		totalFees += prioItem.fee
		txFees = append(txFees, prioItem.fee)
		txSigOpCounts = append(txSigOpCounts, numSigOps)

		minrLog.Tracef("Adding tx %s (priority %.2f, feePerKB %.2f)",
			prioItem.tx.Sha(), prioItem.priority, prioItem.feePerKB)

		// Add transactions which depend on this one (and also do not
		// have any other unsatisified dependencies) to the priority
		// queue.
		if deps != nil {
			for e := deps.Front(); e != nil; e = e.Next() {
				// Add the transaction to the priority queue if
				// there are no more dependencies after this
				// one.
				item := e.Value.(*txPrioItem)
				delete(item.dependsOn, *tx.Sha())
				if len(item.dependsOn) == 0 {
					heap.Push(priorityQueue, item)
				}
			}
		}
	}

	// Now that the actual transactions have been selected, update the
	// block size for the real transaction count and coinbase value with
	// the total fees accordingly.
	blockSize -= wire.MaxVarIntPayload -
		uint32(wire.VarIntSerializeSize(uint64(len(blockTxns))))
	coinbaseTx.MsgTx().TxOut[0].Value += totalFees
	txFees[0] = -totalFees

	// Calculate the required difficulty for the block.  The timestamp
	// is potentially adjusted to ensure it comes after the median time of
	// the last several blocks per the chain consensus rules.
	ts, err := medianAdjustedTime(chainState, timeSource)
	if err != nil {
		return nil, err
	}
	requiredDifficulty, err := blockManager.CalcNextRequiredDifficulty(ts)
	if err != nil {
		return nil, err
	}

	// Create a new block ready to be solved.
	merkles := blockchain.BuildMerkleTreeStore(blockTxns)
	var msgBlock wire.MsgBlock
	msgBlock.Header = wire.BlockHeader{
		Version:    generatedBlockVersion,
		PrevBlock:  *prevHash,
		MerkleRoot: *merkles[len(merkles)-1],
		Timestamp:  ts,
		Bits:       requiredDifficulty,
	}
	for _, tx := range blockTxns {
		if err := msgBlock.AddTransaction(tx.MsgTx()); err != nil {
			return nil, err
		}
	}

	// Finally, perform a full check on the created block against the chain
	// consensus rules to ensure it properly connects to the current best
	// chain with no issues.
	block := btcutil.NewBlock(&msgBlock)
	block.SetHeight(nextBlockHeight)
	if err := blockManager.CheckConnectBlock(block); err != nil {
		return nil, err
	}

	minrLog.Debugf("Created new block template (%d transactions, %d in "+
		"fees, %d signature operations, %d bytes, target difficulty "+
		"%064x)", len(msgBlock.Transactions), totalFees, blockSigOps,
		blockSize, blockchain.CompactToBig(msgBlock.Header.Bits))

	return &BlockTemplate{
		block:           &msgBlock,
		fees:            txFees,
		sigOpCounts:     txSigOpCounts,
		height:          nextBlockHeight,
		validPayAddress: payToAddress != nil,
	}, nil
}