func (tp *TransactionPool) requiredFeesToExtendTpool() types.Currency {
	if tp.transactionListSize < TransactionPoolSizeForFee {
		return types.ZeroCurrency
	}
	ratioToTarget := float64(tp.transactionListSize) / TransactionPoolSizeTarget
	feeFactor := math.Pow(ratioToTarget, TransactionPoolExponentiation)
	return types.SiacoinPrecision.MulFloat(feeFactor).Div64(1000)  
}
requiredFeesToExtendTpool returns the amount of fees required to extend the
transaction pool to fit another transaction set. The amount returned has the
unit 'currency per byte'.
package transactionpool
import (
	"errors"
	"fmt"
	"math"
	"time"
	"github.com/NebulousLabs/Sia/build"
	"github.com/NebulousLabs/Sia/crypto"
	"github.com/NebulousLabs/Sia/encoding"
	"github.com/NebulousLabs/Sia/modules"
	"github.com/NebulousLabs/Sia/types"
)
var (
	errEmptySet            = errors.New("transaction set is empty")
	errFullTransactionPool = errors.New("transaction pool cannot accept more transactions")
	errLowMinerFees        = errors.New("transaction set needs more miner fees to be accepted")
	errObjectConflict      = errors.New("transaction set conflicts with an existing transaction set")
)
func relatedObjectIDs(ts []types.Transaction) []ObjectID {
	oidMap := make(map[ObjectID]struct{})
	for _, t := range ts {
		for _, sci := range t.SiacoinInputs {
			oidMap[ObjectID(sci.ParentID)] = struct{}{}
		}
		for i := range t.SiacoinOutputs {
			oidMap[ObjectID(t.SiacoinOutputID(uint64(i)))] = struct{}{}
		}
		for i := range t.FileContracts {
			oidMap[ObjectID(t.FileContractID(uint64(i)))] = struct{}{}
		}
		for _, fcr := range t.FileContractRevisions {
			oidMap[ObjectID(fcr.ParentID)] = struct{}{}
		}
		for _, sp := range t.StorageProofs {
			oidMap[ObjectID(sp.ParentID)] = struct{}{}
		}
		for _, sfi := range t.SiafundInputs {
			oidMap[ObjectID(sfi.ParentID)] = struct{}{}
		}
		for i := range t.SiafundOutputs {
			oidMap[ObjectID(t.SiafundOutputID(uint64(i)))] = struct{}{}
		}
	}
	var oids []ObjectID
	for oid := range oidMap {
		oids = append(oids, oid)
	}
	return oids
}