202 lines
6.8 KiB
Go
202 lines
6.8 KiB
Go
// Copyright (c) 2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package txsizes
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import (
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"github.com/btcsuite/btcd/blockchain"
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"github.com/btcsuite/btcd/wire"
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)
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// Worst case script and input/output size estimates.
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const (
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// RedeemP2PKHSigScriptSize is the worst case (largest) serialize size
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// of a transaction input script that redeems a compressed P2PKH output.
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// It is calculated as:
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//
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// - OP_DATA_73
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// - 72 bytes DER signature + 1 byte sighash
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// - OP_DATA_33
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// - 33 bytes serialized compressed pubkey
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RedeemP2PKHSigScriptSize = 1 + 73 + 1 + 33
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// P2PKHPkScriptSize is the size of a transaction output script that
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// pays to a compressed pubkey hash. It is calculated as:
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//
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// - OP_DUP
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// - OP_HASH160
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// - OP_DATA_20
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// - 20 bytes pubkey hash
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// - OP_EQUALVERIFY
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// - OP_CHECKSIG
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P2PKHPkScriptSize = 1 + 1 + 1 + 20 + 1 + 1
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// RedeemP2PKHInputSize is the worst case (largest) serialize size of a
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// transaction input redeeming a compressed P2PKH output. It is
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// calculated as:
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//
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// - 32 bytes previous tx
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// - 4 bytes output index
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// - 1 byte compact int encoding value 107
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// - 107 bytes signature script
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// - 4 bytes sequence
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RedeemP2PKHInputSize = 32 + 4 + 1 + RedeemP2PKHSigScriptSize + 4
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// P2PKHOutputSize is the serialize size of a transaction output with a
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// P2PKH output script. It is calculated as:
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//
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// - 8 bytes output value
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// - 1 byte compact int encoding value 25
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// - 25 bytes P2PKH output script
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P2PKHOutputSize = 8 + 1 + P2PKHPkScriptSize
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// P2WPKHPkScriptSize is the size of a transaction output script that
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// pays to a witness pubkey hash. It is calculated as:
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//
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// - OP_0
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// - OP_DATA_20
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// - 20 bytes pubkey hash
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P2WPKHPkScriptSize = 1 + 1 + 20
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// P2WPKHOutputSize is the serialize size of a transaction output with a
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// P2WPKH output script. It is calculated as:
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//
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// - 8 bytes output value
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// - 1 byte compact int encoding value 22
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// - 22 bytes P2PKH output script
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P2WPKHOutputSize = 8 + 1 + P2WPKHPkScriptSize
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// RedeemP2WPKHScriptSize is the size of a transaction input script
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// that spends a pay-to-witness-public-key hash (P2WPKH). The redeem
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// script for P2WPKH spends MUST be empty.
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RedeemP2WPKHScriptSize = 0
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// RedeemP2WPKHInputSize is the worst case size of a transaction
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// input redeeming a P2WPKH output. It is calculated as:
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//
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// - 32 bytes previous tx
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// - 4 bytes output index
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// - 1 byte encoding empty redeem script
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// - 0 bytes redeem script
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// - 4 bytes sequence
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RedeemP2WPKHInputSize = 32 + 4 + 1 + RedeemP2WPKHScriptSize + 4
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// NestedP2WPKHPkScriptSize is the size of a transaction output script
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// that pays to a pay-to-witness-key hash nested in P2SH (P2SH-P2WPKH).
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// It is calculated as:
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//
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// - OP_HASH160
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// - OP_DATA_20
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// - 20 bytes script hash
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// - OP_EQUAL
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NestedP2WPKHPkScriptSize = 1 + 1 + 20 + 1
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// RedeemNestedP2WPKHScriptSize is the worst case size of a transaction
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// input script that redeems a pay-to-witness-key hash nested in P2SH
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// (P2SH-P2WPKH). It is calculated as:
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//
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// - 1 byte compact int encoding value 22
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// - OP_0
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// - 1 byte compact int encoding value 20
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// - 20 byte key hash
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RedeemNestedP2WPKHScriptSize = 1 + 1 + 1 + 20
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// RedeemNestedP2WPKHInputSize is the worst case size of a
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// transaction input redeeming a P2SH-P2WPKH output. It is
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// calculated as:
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//
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// - 32 bytes previous tx
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// - 4 bytes output index
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// - 1 byte compact int encoding value 23
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// - 23 bytes redeem script (scriptSig)
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// - 4 bytes sequence
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RedeemNestedP2WPKHInputSize = 32 + 4 + 1 +
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RedeemNestedP2WPKHScriptSize + 4
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// RedeemP2WPKHInputWitnessWeight is the worst case weight of
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// a witness for spending P2WPKH and nested P2WPKH outputs. It
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// is calculated as:
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//
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// - 1 wu compact int encoding value 2 (number of items)
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// - 1 wu compact int encoding value 73
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// - 72 wu DER signature + 1 wu sighash
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// - 1 wu compact int encoding value 33
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// - 33 wu serialized compressed pubkey
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RedeemP2WPKHInputWitnessWeight = 1 + 1 + 73 + 1 + 33
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)
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// SumOutputSerializeSizes sums up the serialized size of the supplied outputs.
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func SumOutputSerializeSizes(outputs []*wire.TxOut) (serializeSize int) {
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for _, txOut := range outputs {
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serializeSize += txOut.SerializeSize()
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}
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return serializeSize
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}
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// EstimateSerializeSize returns a worst case serialize size estimate for a
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// signed transaction that spends inputCount number of compressed P2PKH outputs
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// and contains each transaction output from txOuts. The estimated size is
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// incremented for an additional P2PKH change output if addChangeOutput is true.
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func EstimateSerializeSize(inputCount int, txOuts []*wire.TxOut, addChangeOutput bool) int {
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changeSize := 0
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outputCount := len(txOuts)
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if addChangeOutput {
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changeSize = P2PKHOutputSize
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outputCount++
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}
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// 8 additional bytes are for version and locktime
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return 8 + wire.VarIntSerializeSize(uint64(inputCount)) +
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wire.VarIntSerializeSize(uint64(outputCount)) +
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inputCount*RedeemP2PKHInputSize +
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SumOutputSerializeSizes(txOuts) +
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changeSize
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}
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// EstimateVirtualSize returns a worst case virtual size estimate for a
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// signed transaction that spends the given number of P2PKH, P2WPKH and
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// (nested) P2SH-P2WPKH outputs, and contains each transaction output
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// from txOuts. The estimate is incremented for an additional P2PKH
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// change output if addChangeOutput is true.
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func EstimateVirtualSize(numP2PKHIns, numP2WPKHIns, numNestedP2WPKHIns int,
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txOuts []*wire.TxOut, changeScriptSize int) int {
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outputCount := len(txOuts)
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changeOutputSize := 0
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if changeScriptSize > 0 {
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changeOutputSize = 8 +
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wire.VarIntSerializeSize(uint64(changeScriptSize)) +
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changeScriptSize
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outputCount++
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}
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// Version 4 bytes + LockTime 4 bytes + Serialized var int size for the
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// number of transaction inputs and outputs + size of redeem scripts +
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// the size out the serialized outputs and change.
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baseSize := 8 +
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wire.VarIntSerializeSize(
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uint64(numP2PKHIns+numP2WPKHIns+numNestedP2WPKHIns)) +
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wire.VarIntSerializeSize(uint64(len(txOuts))) +
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numP2PKHIns*RedeemP2PKHInputSize +
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numP2WPKHIns*RedeemP2WPKHInputSize +
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numNestedP2WPKHIns*RedeemNestedP2WPKHInputSize +
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SumOutputSerializeSizes(txOuts) +
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changeOutputSize
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// If this transaction has any witness inputs, we must count the
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// witness data.
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witnessWeight := 0
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if numP2WPKHIns+numNestedP2WPKHIns > 0 {
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// Additional 2 weight units for segwit marker + flag.
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witnessWeight = 2 +
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wire.VarIntSerializeSize(
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uint64(numP2WPKHIns+numNestedP2WPKHIns)) +
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numP2WPKHIns*RedeemP2WPKHInputWitnessWeight +
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numNestedP2WPKHIns*RedeemP2WPKHInputWitnessWeight
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}
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// We add 3 to the witness weight to make sure the result is
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// always rounded up.
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return baseSize + (witnessWeight+3)/blockchain.WitnessScaleFactor
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}
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